& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (2024)

& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (1)

TH=01111:42G11101:11112011* INAL


JULY 1987

Capacitors -techniquesandapplications

Curls, grads,divs and dels

Real-timecolour palette

Mobile radioupdate

V.h.f. voltage -


Class Bcrossoverdistortion

Denmark DKr. 63.00 Germany DM 12.00 Greece Dra. 680.00 Holland DFI. 12.50 Italy L 6500 Spain Ptas. 700.000

Singapore SS 11.25 Switzerland SFr. 9.50 USA S 6.50.

& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (2)

CliECTRONIC BROKERSThis is just a sample of our huge inventory - contact us with your requirements.OSCILLOSCOPES

Hewlett Packard180 TR 100MHz Scope Mainframe

(Mint)PhilipsPM3266 100MHz Storage ScopePM3305P 35MHz Digital Storage.] onlyPM3540 Logic Anal/ScopeTektronix465B/DM44100MHz Scope/DMM4658100MHz Scope475A/DM44 200MHz Scope/DMM485350MHz Scope608 Monitor634 opt 1,20 Display

Monitor5223 Scope M/F (Mint)71041 GHz Scope M/F7603100MHz NVF7704A 200MHzMainframe £28507834 Fast Storage ScopeM/F £7500R7603 100 MHz RackMINT M/F £17507904 500 MHz ScopeM/F £5500A large selection of7000 series plug -insavailable at up to 60%saving on list. Pleasecall for quotations.








Hewlett Packard141T DisplayMainframe £20003580A SpectrumAnalyser3582A SpectrumAnalyser4193A ImpedanceAnalyser8552B IF Section




8553B RF Section,110MHz £2650MarconiIF 2300A Mod Meter £495TF 2370 110MHz SpectrumAnalyser £7250TF 2371 200MHz Spectrum Analyser £6500Tektronix7L14 Spectrum Analyser P. In308 Data Anal ser


SIGNAL SOURCESHewlett Packard4204A Digital Oscillator8007B Pulse Generator8011A-001 Pulse Generator

20MHz8601 A SweepGenerator86408/001/002 Signal Generator

1024MHz86260A Sweep Gen. Plug-in12.4 -18GHzMarconi2015-1 ANVFM Signal

GeneratorTF 2002B AM/FM Signal Generator






PhilipsPM5519ITV Pattern GeneratorWavetek1 84MHz Sweep Generator1080 1GHz Sweeper




RTE85A Microcomputer86A Microcomputer110 (45710BU) The Portable'150B Touchscreen2673A Thermal Printer6940B Multiprogrammer7470A opt 001/002 A4 2 -pen plotter7475A opt 002 A3/A46 -pen plotter7910H opt 015 Disk Drive82913A 12 inch Monitor82938A HPIL Interface82939A Serial Interface82940A GPIO Interface9111A Graphics Tablet9121D Single -sided Disc Drive91 22D Dual Double -sided Disc Drive91 33XV 1 5MB & 270KB Disk Drive




9845A Desk Top Computer9816A Personal Computer9825A opt 001-002 Desk Top

Computer98256A 256K RAM board,

series 200991 5AComputer




GENERAL PURPOSE T &FarnellSSG 520 TTS 520 Transmission

Test Set

Fluke7220A Comms. Freq. Counter £350

Hewlett Packard4282A-001 Digital High

Capacitance Meter £750436A Power Meter £1050

467AAmplifier £6003403C True RMS

Voltmeter £18503406A Sampling

0 Voltmeter £12503465A 4' DigitD.M.M. £1005300B + 5305B 1300MHz Counter £4955381A 80 MHzCounter £2258447A Amplifier £4008447D Amplifier £600MarconiTF1 245A Q meter

£750TF 1246Oscillator £500TF 1313A LCR Bridge0.1% £750

TF 2173Synchroniser

for2016 £450TF 2603 RF

Millivoltmeter £300TF 2604 Voltmeter £425

TF 2702 InductorAnalyser £950

TF 2905/8 TV PulseGenerator £650

TF 2915 Data Monitor £1200TF 2950/5 Mobile Radio T.S. £1350PhilipsPM5580 IF Modulator £3000PM5581 RF Convertor £1000PM5582 RF Convertor £1000Tektronix520AVectorscope(NTSC)521A PAL VectorscopeSi Sampling HeadS.3A Sampling Head1411C opt 03 TV Signal GeneratorA6901 Isolation Monitor4041 System ControllerP6451 DA ProbePM 102 Personality ModulePM 108 Personality Module







All prices are exclusive of VAT and correct at time of going to press Carriage and packing charges extra A copy of our trading conditions is available on request


Electronic Brokers


) Electronic Brokerso 140-146 Camden Street, London NW1 9PBo U Fax: 01-2677363. Telex: 298694. Tel: 01-2677070ENTER I ON REPLY CARD

& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (3)



Research into biohybrid integrated circuitsinvolves interconnections betweenneurons. Nerve cells in this electron

micrograph are between a quarter and atenth of a micron across. Last month's

cover, which carried an incorrect caption,was an internal view of Motorola's 68020

32bit microprocessor.


671The new architecture makes all bus devicesintelligent so that bus activity is local to the

processors, thus leaving the bus free fordata transfer

by David Hunt and Keith Hodson.


This years MRUA conference coincided withpublication of the government -sponsored

report on spectrum deregulation.


688Historically, the somewhat slow -moving

and technologically mature capacitorindustry has been overlooked by investment

interest and p.r. hype. But there arechanges afoot, both in market and industry...

by Keith Thomas


690Engineers should have a good appreciation

of the cost of various technologies for agiven capacitance value

by Martin Baker


692The low cost of nickel barriers vs the

reliability of silver -palladium.


697."If Maxwell's theory is about to be displaced

we might take a nostalgic look at it onceagain"

by Joules Watt


By 1990 a typical car might contain 500capacitors, say AVX of Aldershot. leadingto a very large volume of production if theestimate of 10 million new cars in Europeis realistic. See page 688 for an analysisof Europe's capacitor market.


699Bipolar i.c. technology has produced fastprescalers with a phase noise and speed -

power performance better than with GaAs.


705A well -placed dipole can often give betterresults than indoor Yagi or logarithmic



707Analysis of noise behaviour for a variety of

v.h.f. transistors shows that a j-fetproduces the lowest phase noise

by A. Decker


710Suite of Pascal programs calculates gain,

impedance, current distribution andradiation pattern for any geometry, element

thickness and operating frequency.by C.J. Railton


716by W.A. Atherton


718If you are about to decide on a computerlanguage for your next industry controlsystem, one of the new breed of Pascal

compilers may be ideal.by William Stanley


Fast look -up table enables frame store tomanipulate moving images in real time for

flicker -free effectsby D.E.A. Clarke


727External cache with 25ns rams can takecare of repetitive loops with the 68020

by D.Burns and D.Jones


735by B.J. Sokol


739Detailed tests on three amplifier modes,

including a non -switching form of class B,give rise to some interesting conclusions

by Erik Margan


Under Leeds University's Department ofElectrical and Electronic Engineering this

exhibition claims to be the bestin electronics outside London.








PRODUCTS 743 to 751







& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (4)





HEWLETT PACKARD1630G Logic state &timing.65ch. 100MHzclock...£7950

4951A/1/100 PortableProtocol Analyser forserial data..£2500

TEKTRONIX834 Datacom/ProtocolAnalyser...£2000


PHILIPSPM3266 100MHz Faststorage.Dual trace dualtimebase...£2950

TEKTRONIX2215 60MHz dual tracewith delay...£625

2445 150MHz fourtrace.Dual timebase.£2190

2465 300MHz four tracewith delay..£3200

7623A/7A18/7B53A 75MHzFast storage.Dual trace.Dual t/base..£1500


HEWLETT PACKARD141T/8552B/8555A System0.01-18GHz.£7500 or with model8445 pre-selector..£9000

3561A/001 DynamicSignal Analyser....£7950

MARCONIff7YNT 110MHz analyserwith trackinggenerator....£6850

SOLARTRON1200 Dual channel L.F.SignalProcessor/Analyser.£7250


MARCONI2019 1GHz AM/FM phaselocked.HP-IB..£2950

PHILIPSPM5190 1mHz-2Mhz phaselocked.HP-IB£1050



State/Timing/Glitch43ch. 100MHz.Clock mux..£4250



6ch.flatbed. Overlappingpens. I/P voltages lmV-500V..£500.



Int. memory + datatape. Up to 19.2kbps..£3250


INTELSeries 2Series 3Series 4 & PDS seriessystems are allavailable.CHECK NOW FOR BESTPRICES:

HEWLETT PACKARD64100A/041 Logicdevelopment station.....£5900

64600 Logic TimingAnalyser...£2500



CENTRONICS353 200cps dot matrixprinter. Centr. & RS232I/F. +NLQ mode ..£350

EPSONFX100 MatrixPrinter...£.325

MX100 MatrixPrinter...£.195

HEWLETT PACKARD7475A/2 Eight penplotter HP-IB..£800

82901A Dual Disc DriveHP-IB...£150

9817 Modular computerworkstation....£1800

9826A Technical computer/ controller. Internaldisc...£1500


Prices EXCLUDE delivery& V.A.T.


Stocks are always changing: If your requirement is not listed thenplease phone: WE MAY WELL BE ABLE TO HELP YOU !


Cardwell Carstolf:CARSTON ELECTRONICS LTD. 3 Park Rd. Teddington. Middx. TW11 OAF Tel. 01-943-4477 Telex. 938120 CARLEC-G


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (5)


EDITORPhilip Darrington

DEPUTY EDITORGeoffrey Shorter, B.Sc.

01-661 8639

TECI INICAI, EDITORMartin Eccles01-661 8638


01-661 3039

NEWS EDITORDavid Scobie01-661 8632


01-661 8676Roger Goodman

ADVERTIsem*nT MANAGERMartin Perry01.6613130

Michael Downing01-661 8640

CLASSIFIED EXECUTIVESusan Platts01-661 3033


(Make-up and copy)01-661 8648Jackie Perry01-661 8649PUBLISHER

Shobhan Gajjar01-661 8452

Embarrasde richesse

Whenever an engineering development to improve services is madepossible, the broadcasting organizations are at pains to ensure thatexisting equipment is not rendered obsolete or, if it is made

incompatible, long periods are allowed for any necessary changeover. One cancite the move to 625 -line television: the introduction of f.m. radio; the start ofcolour: the incorporation of teletext - all these were brought about painlessly,at no cost to those users who did not want the new service, except for the625 -line change which took place over more than 20 years, and in some caseswithout the user even being aware of the development. These organizationshave a duty to bring about change in this way and take a great deal of trouble todo so. They are concerned chiefly with providing the best possible service andthe profit motive is absent.

But what of development in the rest of the consumer electronics market? Itappears that no such scruples can exist alongside the need to create newmarkets. Each new development that emerges from the multinationals is, ofcourse, an improvement on previous products, but at what cost to the public?

Admittedly, there are those who will acquire the newest, simply because it isavailable. But, if the majority have been persuaded to buy cassette recordersand black disc turntables at great expense, it is surely not unnatural for themto feel aggrieved when the next development uses optical discs and is totallyincompatible with their equipment. If a music lover possesses a collection ofcassettes, built up over ten years, does not the impending introduction ofdigital audio tape fill him with alarm and despondency?

It would be naive to expect the manufacturers of domestic electronicequipment collectively to refrain from introducing new techniques to themarket until the previous generation of equipment had had a reasonable run,but there must surely be a less cynical way of progressing than to rendercollections of hardware and "firmware" obsolete at a stroke. The very least thatcan be done is to allow existing technology an extended period of obsolescence.

The consumer society is becoming, or has become, the victim of the pursuitof technology for its own sake. So far, society has been tolerant and even eagerfor new technology, but in the face of time scales of introduction andobsolescence which are shrinking to the point of bewilderment, it musteventually begin to react: the diminishing returns of "investment" in newmethods of playing recorded music or watching television cannot escape noticefor ever.

El. Mon 'us & World is published monthlyUSPS 6875414 Curnmt issue price (1.95, back issues naavailable'(2.10 at Itetad and Trade Counter. Units l& BanksideIndustrial Centre. Iloptim Street. London SE1 Telephone:01412/4 :1567. By post, current issue £2.25. back issues 'ifAValtabil-1 £2.50. Order and payments to 301 EIrrimmt,and Wireless World. Quadrant Douse. The Quadrant.Stilton. Surrey SM2 5AS. Cheques should be payable toReed Business Publishing Ltd. Editorial & Advertisingoffices: EWW Quadrant House. The Quadrant. Sutton.Surrey SM2 5AS. Telephones: Editorial 01-661 3614.Advertising 01.661 3130 111-661 8469 Telex: 892010B1SPRS B IEE1'. Facsimile: 014;61 3948 'Groups II &Beeline: 01.661 M978 or 01-661 8486.:1111 baud. 7 data bits,even parity. stop -bit. Send ctrl -Q. then EWW to start:NNNN tii sign MT. Subscription rates: I year 'normal

ratio 123.40 (IN and £28.50 outside (IE. Distribution:quadrant !louse. The Quadrant. Sutton. Surrey SM2 5ASTelephone 01-661 32414. Subscriptions: ()Afield !louse.l'errymount Road. Hayward': Heath. Sussex 81116 :11)11.Telephone 04444 59188. Please notify a change of addressUSA: $116.00 airmail. Reed BusinessPublishing USA'. Subscript imis Office. 205 E. 42nd Street.NY 10117. Overseas advertising agents: France andBelgium: Pierre Mussard, 18-20 Place de la Madeleine.Paris 750194. United Stales of America: Lay Feitintaii.Reed Business Publishing lad. 2115 East 42nd Street.New York. NY 10017 Telephone 12121 887.2080 Telex23827. USA mailing agents: Mercury Airfreight Inter-national Ltd. Inc.. 10161 Englehard Ave, Avenel N.J. 071811.2nd class postage paid :it Rahway N.J. Postmaster - sendaddress to the almve.

)keel Business Publishing lad 1987. ISBN 19143 61162


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (6)

GASFET RF PREAMPLIFIERSThese amplifiers provide the best noise performance available. Suitable for laboratory work or masthead use.Aligned to your specified frequency in the range of 30-1000MHz.

TYPE 9006 N.F. 0.6 dB. Gain 10-40 dB variable. In the range 30-250 MHz . . . £71 £3 p&p. TYPE 9006FM As9006. Band II 88-108 MHz . . . £71 + £3 p&p. TYPE 9002 Two stage Gasfet preamplifier N.F. 0.7 dB. Gain 25 dBadjustable. High Q filter. Tuned to your specified channels in bands IV or V . . . £93 + £3 p&p. TYPE 9004UHF two stage Gasfet preamplifier N.F. 0.7 dB. Gain 25 dB adjustable. High Q filter. Aligned to your specifiedfrequency in the range 250-950 MHz . . £93 + £3 p&p. TYPE 9035 Mains power supply unit for abovepreamplifiers . . . £27.00 + £4 p&p. TYPE 9010 Masthead weatherproof unit for above preamplifiers . . . £11 +£3 p&p.

RF SIGNALS SOURCES 10 MHz -1 GHzHigh stability phase locked oscillators operating directly on the signal frequency using a low frequencyreference crystal. Miniature modules capable of accepting NBFM or FSK up to 3 KHz deviation which willeffectively replace expensive signal generators in the lab to provide single specified frequencies. Linearamplifers are available to increase output power. TYPE 8034 Specify output in the range 10-150 MHz. Output10 mW ( + 10 dBm) . . . £109 + £3 p&p. TYPE 8036 Specify output in the range 150-1000 MHz. Output 10mW . . .


Transmitting frequency converter provides the performance required for television retransmission systems.TYPE 9113 . . . £324 + £6 p&p. Receiving frequency converter for weak signal reception . . . TYPE 9114. . . £324 + £6 p&p.

BAND II FM TRANSMITTERSingle channel high stability phase locked loop FM exciter. 50 watts RF output. Complete in 19" racking casewith mains power supply and fan cooling.

TYPE 9292A (Mono) . . . £1496 + £40 p&p TYPE 9292B (Stereo) . . . £1794 + £40 p&pComplete amplifier and retransmission systems supplied with connectors. Comprehensive range of RF linearpower amplifiers also available. Write or phone for full technical information.

Please add 15% VAT on total for UK sales. Please contact sales office for overseas post and packing rates.






PINEAPPLE SOFTWAREPrograms for BBC computers with disc drive. FREE updating service on all software.

DIAGRAMStill the only drawing program avai able for the BBC micro which gives you the ability to draw really large

diagrams and scroll them smoothly around the screen stopping to edit them at any time if requiredPineapple s unique method of storing the diagram information on disc means that the size of diagrams is

limited only by the free space on disc and not the amount of computer memory you have available IA blank80 track disc will allow up to 39 mode 0 screens of diagram(

The superb print routine( supplied with the program enable large areas of the diagram to be printed in asingle print run in a number of different sizes and rotated through 90 deg if required Full use can also bemade of printers which have a wider than normal carriage available

The program is fully compatible with the Marconi Tracker ball described below


PRICE £25.00 VAT

DIAGRAM UTILITIESA suite of six utility programs w' ''' f) .ftram drawing program The utilities

include the saving and loading of areas of diagram to and from disc Tne ability to disblay the whole of yourlarge diagram on the screen at one time tin either 4*4 or 8*8 screen format) Tne addition of borders andscreen indents to diagrams. and the ahrav I,. shift a whole diagram in any direction

PRICE £10.00 + VAT

PCBThis new releaSe from Pineapple is a printed circuit board draughting aid which is aimed at producing

complex double sided PCBs very rapidly using a standard BBC micro and any FX compatible dot-matrixprinter

The program is supplied >n EPROM and will run with any 32k BBC micro (including Master series) Alsosupplied is a disc containing a sample PCB layout to demonstrate the programs features

By using an EPROM for the program code the maximum amount of RAM is available for storing componentlocation and ASCII identification files etc I Up to 500 components and 500 ASCII component descriptionsmay be stored for a given layout) These is no limit to the number of tracks for a given PCB, aitnougn themaximum size of board is restricted to 8- ' 5 6 -

Using a mode 1 screen. tracks on the top side of the board are shown in red. while those on the undersideare blue Each side of the board may be shown individually or superimposed A component placement screenallows component outlines lo be drawn for silk screen purposes and component numbers entered on thisscreen may be displayed during track routing to aid identification of roundels

The print routines allow separate printouts of each side of the PCB in a very accurate expanded definition1 1 or 2 1 scale enabling direct contact printing to be used on resist covered copper clad board

This program has too marry superb features to describe adequately here. so please write or phone for moreinformation and sample prinouts

PRICE £85.00 VAT

MARCONI TRACKER BALLThis high quality device comes with it s own Icon Artmaster drawing program and utilities tuenable it to be

used in place of keyboard keys Joysticks or with your own programsFor Model B & B with icon Artmaster) 460 00 VAT Bare Trackman Ino software) 449 00 VATFor Master Series with Pointer ROM1 460 00 VAT Pointer ROM available separately 412 50 VAT

P&P on Trackerballs V 75

TRACKERBALL ADAPTORSConverter leads to enable the TraCkerball to run mouse software and the mouse to run trackerball software

Iinc DIAGRAM) Please state which way round when ordering

PRICE £8.00 t VAT

ADFS Utilities ROMADU is a new product which will prove invaluable to all users of the ADFS (Including Winchester ownersl

The ADU Rom allows direct access to utilities which previously required the use of the ADFS utilities disc

Many novel features are included in the commands allowing such facilities as the copying plan the Meson a DESdisc onto ADFS in a single pass and Backing up between discs of different size (including Winchesters)

There is also a very powerful sector editor with automatic correction of CRC bytes and a menu routine with over30 possible operations on ADFS discs

Please write or phone for more details

PRICE £29.00 VAT

MITEYSPICEA new addition to our range 01 engineering software Miteyspice is a very powerful DC and AC analogue circuit

simulator package with graphic display for any model BBC computer

As well as ail the usual facilities available with this type of program non-linear effects. small signal noisemeasurements and sweeps may be performed Component values may be swept. allowing component tolerances tobe investigated as well as thermal performance etc Comprehensive transistor modelling is incorporated using a 20parameter Ebers Moll description The program is supplied on disc with a very comprehensive 49 page manualPlease write or phone for more i,!.,nt



luz. 39 Brownlea Gardens, Seven Kings, Ilford, Essex 1G3 9NL. TA` Tel: 01-599 14760ENTER 47 ON REPLY CARD


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (7)








plus p & p and VAT

adjustable temperature simple plug in 4.75mm tipsin handle full supporting tip range

electronic thermostat control low voltage power pack- no moving parts 24v 50v AC

spike and potential free

DCOLP\rit.ve ,esWeir


FOR FULL DETAILSon all ADCOLA equipmentcontact Sales Department...

ADCOLA PRODUCTS LIMITED Gauden Road London SW4 6LHTelephone Sales (01) 622 0291 Telex 21851 Adcola GSales Offices also at Bristol Bournemouth Preston Glasgow


DM 105 - Pocket DVM fromA meter to literally suit allpockets - including the onethat holds the wallet!Its small size offers easy one hand operation, with large, clear,wide-angle display.But small does not mean delicate; the DM105 can withstand a 12inch drop without damage, due to its glass epoxy PC boards.shock mounted display and through thermoplastic case.Overloads are handled with similar certainty; the resistancerange is protected up to 500 dc. AC voltage range to 14XIV rmsand DC voltage ranges up to 1000V.Battery life is typically 2000 hours and a LO BATT indicatorsignals 20% battery life remaining.RangesDC Volts: 2V, 20V, 200V, I kVAC Volts 200V, 750VFreq Range: 45Hz - 450HzDC Current: 2 mA. 20 mA,

2(X) mA, 2AResistance: 2K. 20K, 200K, 2MDC Accuracy:

-± (0.5% reading - 2 digits)Size: 130 x 75 x 28mmWeight: I95gAccessories: Battery, test leadsand manual.

Price £24.75 Inc VATPlease add 70p for post and packing.

This is just one of our range of quality Analogue and Digitalmultimeters.

Full details and specifications from:

Cirkit Distribution LtdPark Lane, Broxbourne, Herts ENIO 7NciTelephone ( 0992) 444111 Telex: 22478





serious CAD atlighthearted prices


- reallyusefulpeople

IBM UsersFor PC

softwareplease seeour advert

on page 669

Probe wound Miteyspice'scomputer model of your circuit.More informative, more fun andfaster than a breadboard. Plot theAC & DC characteristics. quantitybandwidth with the digitisingcursor, sweep compone-its,investigate temperature and noise(20 param Ebers Moll model) andwhen perfect, lay it out and etch itaccurately with PCB using anordinary DM printer. Theseprograms have too many superbfeatures to cover here, please sendfor details.

* Just released *MITEYSPICE

incorporating the unbeatableMicrospice circuit simulator

(£119 r VAT)

P.C.B.Pineapple's acclaimed "a utility Ithoroughly recommend" JulianRogers Micro User March '87circuit board drafting program

(£85 + VAT)

Postal address, callers by appointmentTel: 106a Fortune Green Road Tlx:

01-435 West Hampstead 89505112771 London NW61 DS Mari, km mailbox


THOSE ENGINEERS Ltd(also at Fairoaks Airport, Chobham)





& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (8)

The Archcr Z80 6I)CThe SDS ARCHER - The Z80 based single boardcomputer chosen by professionals and OEM users.* Top quality board with 4 parallel and 2 serial ports,

counter -timers, power -fail interrupt, watchdog timer,EPROM & battery backed RAM.

* OPTIONS: on board power supply, smart case,ROMable BASIC, Debug Monitor, wide range of I/O &memory extension cards.

from £185 + VAT.ENTER 45 ON REPLY CARD

The nowman 68000 613CThe SDS BOWMAN - The 68000 based single boardcomputer for advanced high speed applications.* Extended double Eurocard with 2 parallel & 2 serial

ports, battery backed CMOS RAM. EPROM, 2 counter -

timers, watchdog timer, powerfail interrupt, & anoptional zero wait state half megabyte D -RAM.

* Extended width versions with on board power supplyand case.

from £295 + VAT.ENTER 46 ON REPLY CARD

6hcrwood L)alacSystems LtdSherwood House, The Avenue, Farnham Common, Slough S1,2 3JX. Tel. 02814-5067


TRAINING FOR TRAINERSLAB -VOLT will be conducting a series of one day seminars on thefollowing technologies:


Audio visual presentations and hands-on experience will be the main part ofthe seminars.A certificate of achievement can be obtained upon satisfactory completionof a voluntary multiple choice test.Please contact LAB -VOLT on 0480 300965 or by fax on 0480 61654for costs and dates.

Lab -Volt, Unit 6 Cromwell Mews, St. Ives, Cambs PE17 4BH, England


1 1 1 ( IItU\ICs,E 1111t1 1 ss 410121 11

& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (9)

New-wave architectureThe performance of traditional bus -based computer systems is

limited by the bus itself. The new architecture makes all thedevices on the bus intelligent, so that most of the activity islocal to these processors and the bus is used for data transfer

rather than program execution.

arA good understanding of systemarchitecture is important for all usersnd potential users of microsystems.

This article describes a novel approach to theproblem of how to arrange the componentsof a microprocessor system to maximize theperformance without excessive complexityand cost.

Modular computer systems made up of aseries of p.c.bs and connected via a back -plane bus were originally developed by thecomputer manufacturers as a way of increas-ing the flexibility of their systems. Thesebus -based systems allowed a wide variety ofsystems to be built from a relatively smallnumber of components, which were thecomputer p.c.bs themselves. A well-knownexample of such a bus, prominent in the1970s, was DEC's Unibus, to which some ofthe current buses, namely STE and VME,bear more than a passing resemblance.

It was the advent of the microprocessorwhich opened up this area to a wider audi-ence. The original four -bit c.p.us were obso-lete before bus standards were created buttheir replacements have spawned a diverserange of buses. The eight -bit buses haveendured longer than most pundits wouldhave predicted at the time of their introduc-tion and in fact the STE standard has onlyrecently emerged.

The first people to bring out bus -basedsystems for general use were the semicon-ductor manufacturers, whose first designscomprised a c.p.u. card, a memory card andi/o function cards, Fig. 1.

The bus was really an extension of themicroprocessor pins and it ran at the samespeed as the processor clock. The bus wasprocessor -specific and used for both pro-gram execution and data movement. Thistype of bus was very easy to implement andin general there was no contention for theuse of the bus, the single c.p.u. being alwaysin control. The bus was limited in the sensethat once the system ran out of power, thatwas it; there was no easy way of increasing it.


The next major advance was to modify thebus so that more than one processor couldwork with the same memory and i/o. Thiswas achieved by adding some arbitrationlogic to determine which device had access



Software concepts have formed an important part of the'new wave design philosophy. Insoftware terms, the language mils at the top level with the hooks into the operating systembelow it The operating system itself calls software modules which control the physicaldevices themselves. In standard VME systems, many of these modules are charged forseparately or else the system engineer has to write them. In the 'new wave' approach, thehardware modules are intelligent and the software is an integral part of the module. It is as ifwe had a 'hardware operating system'.

Figure 1. The old pioneer: This is a simple system n which the bus is an extension of themicroprocessor pins. In some designs the microprocessor address and data lines weretaken directly onto the bus without any intermediate buffering.

Disc Video I/0

Figure 2. Multiprocessors: The performance of a system can be increased by adding asecond processor to the bus. A bus arbitration unit determines which c.p.u. has access tothe bus.

to the bus. If, for example, a c.p.u. needed toaccess bus memory, it had to gain control ofthe bus first. This extra delay causes what isknown as a 'wait state' in the c.p.u. and slowsit down by typically 10%. In fact, the abilityof a c.p.u. to handle wait states is fun-damental for processors in multiprocessorsystemsAThe alternative is to stop the c.p.u.clock temporarily). Adding a second proces-sor to such a bus system did not result in acommensurate increase in performance.The main reason for this is that occasionally,a c.p.u. has to wait for access because the busis already in use. In this type of system, the

bus is the limiting factor in system perform-ance. Fig.2.

The local execution bus technique usesthe multiprocessor bus for data transfers buthas a local bus for program execution. Thisgoes a long way toward alleviating theproblems described, Fig.3. The problem isthat now, one has to be careful in theselection of card types. I have seen a recentlyproduced system with a c.p.u. and localexecution bus, except that, in this case, thedisc controller was only capable of tranfer-ring data into memory on the bus! Thesystem was set up with an extra memory card


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so that accessing data in this memory waspenalised by way of unwanted wait states.The local bus was reserved for the systemstacks only.

This idea can be extended to include anumber of masters, each with their ownexecution buses. The c.p.us each carry onwith their own tasks and the system bus isonly used for intertask communication andi/o accesses. It is now the i/o accesses whichlimit system performance.

To overcome the problem of i/o accesses,an i/o slave bus can be used in conjunctionwith the main system bus. One particularsolution, discussed in a recent issue ofElectronics and Wireless World*, is to put ina bus coupler from the main bus to the i/obus, which in this case were VME and STErespectively.


The ultimate solution for a fixed bus size is toassign to each i/o activity its own c.p.u. andits own local bus. It is now possible, becauseof the low cost of c.p.us and memory, to dothis while keeping the prices of the cardsabout the same as those of the old, non-intelligent predecessors. Each card in thesystem has its own operational software andcan therefore be used with any c.p.u. on thebus. In fact, these cards can be used toimprove the performance of the older systemdescribed earlier.

The implication for system performance isthat if many of the tasks of the system areexecuted in situ, bus activity is reduced. Itsseems paradoxical that we have increasedthe efficiency of a high performance bussystem by using the bus as little as often!

A crucial factor in deciding which bus touse for a given application arises here. Thejustification for eight -bit data buses has beenthat much of the i/o is in this format. This is

STE as an i/o bus in VME systems, by Tim Ellsmore.February issue.

Figure 4. Multiple master with global datamemory: CPUs operate independently ontheir own execution buses, using the globalr.a.m. for intertask communication. Nowthe i/o accesses on the bus are the majorcauses of bottlenecks.

true for serial data, ascii characters for videoand printers, SCSI for disc data and indeedfor CPIB protocol. If this is the case, theargument goes, most i/o operations willinvolve eight -bit transfers, so why go to theexpense of a 16 or 32 -bit bus when a lessexpensive bus will do? Unfortunately, wehave forgotten about the local intelligence ofthe i/o cards. These intelligent i/o cards canpreprocess the data in their local memories.For example, they can join together twobytes to form one 16 -bit word prior totransmission on the bus. In this way, 16 -bitbus data transfers can take place with twicethe throughput of the eight -bit systems.

Our new wave architecture system wouldcomprise the following:

Multiprocessors each with local executionbus Data bus with communication memoryand inter-c.p.u. interrupt facility Intelligent disc processor with local trackbuffer intelligent second management Intelligent video, keyboard and printerprocessor with a fifo buffer Intelligent i/o processor for analogue anddigital i/o Intelligent serial processor with fifo buf-fers XXX processor

XXX means you name it: GPIB, advancedgraphics, etc. This provides a loosely cou-

pled, open architecture providing eleganceand efficiency!


A master is a device which is capable ofinitiating a data transfer, such as a processorcard or a d.m.a. device. A slave is a devicewhich can respond to a master either receiv-ing data from the bus or putting data on tothe bus as required. Traditionally, slaveswere passive, but the new wave architecturefeatures active slave boards.Muter -master communication. If master Awishes to send a message to master B itcannot do so directly. The master addresslines are normally outputs only, so there isno way to establish a destination address forthe data in master B. Therefore, a globalram, which is accessible to all masters, mustbe used. This memory could be found on abus memory card or perhaps dual port ramon one of the masters.

Example: master A sends the string 'Hello'to master B.

A 1. Check semaphore bit is clearA 2. Write message string into message

blockA 3. Set semaphore bit (also causes irq on

master B)B 1. Master B receives vectored interruptB 2. Transfer message from local ramB 3. Clear semaphore bit


Local bus


Figure 3. Local execution bus (above): Technique uses multiprocessor bus for datatransfers and local bus for program execution.

Multiple masters with local memory: Eac1 c.p.u. card can run its own program in its ownmemory. The bus is used to access the slaves including i o. Arbitration and control unitdetermines which device has control of the bus when more than one device requests it.




"aster(Du -1

Local bus



Masterc pu 1

Local bus



Masterc pu2





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The ability to interrupt the receiving masteronce the message has been written to theglobal ram is essential for efficient operationof a multimaster system.

The communication ram is normal on theVME bus. The special feature is the interruptsemaphores. The interrupt vector could alsobe in the ram hence providing multipletransfer types. The standard bus arbitrationdeals with the problem of masters clashingand interrupt priority.

The example shown is parameter blockpassing. The same method can be used forany data length including single bytes.Master -slave communication. Althoughslaves have no mechanism for taking controlof the bus, they may be capable of causingbus interrupts. They are much simpler thanmasters and this is why the 10 processor,described below, is very attractive solutionin the new architecture.

The two commonly used data transfermethods used for slaves are basically thesame as that for masters.1. Using parameter ram: The parameter ramis local to the slave and may also appear onthe bus as i/o data area. It generally does notneed to be dual ported as the transfer of datais always under the control of a master.2. Using first -in -first -out buffer: The slavecan have a single byte for communication(read and write) which is effectively a win-dow into the fifo itself. A status register isused to control the flow of data.


A real example of the new wave architecturehas been implemented by PSI Systems of

The PSI New Wave Architecture showingVMEbus backplane, single -system c p uand the intelligent i/o processor. The i/obus is a low-cost 50 -way ribbon cablewhich connects the i/o processor to thesignal conditioning modules such as relaysand triac outputs. A second 50 -way ribboncable is used for the analogue i/o bus (notshown).

Cambridge on the VMEbus. In this system,the master is a 68000 series c.p.u. capable ofrunning a modern multitasking languageunder an operating system. Its local memorycan easily accommodate 2MByte of ram and2MByte of eprom. The VMEbus active slaveboards include a text processor to controlvideo, keyboard and printer, an i/o processorto control analogue and digital i/o and a discprocessor to control hard and floppy discdrives.

The components of this system are effec-tively asynchronous and can work indepen-dently of each other. In fact, master -slavearchitecture is parallel processing. The keyto the efficiency is that the backplane shouldonly be used for data transfers, and theindividual program execution is done local-ly. The master runs the controlling programat the same time as the slaves individuallyhandle their specific tasks.

Now see how the new wave architectureworks in practice, assuming that one of thetasks on that master requires a disc sectorfetch and a second task is writing to the videoscreen.


The task must first gain access to the discprocessor to avoid collision with anothertask that may already be using the disc. Theprocessor will have a 'test and set' bit for thispurpose in its status byte which is read untilit becomes clear. The test and set instructionwill have left the bit set so that no other taskcan now interfere. The read -sector com-mand is now written to the disc processortogether with any data required

<read sector>, <logical sector number>.

At this point the task suspends. All of theother tasks will be continuing as normal andcan still use the VME bus to access otherslave processors. The disc processor is nowload; ng the required sector into its local dataram which can also be read from the VME-bus. When the sector is ready, the discprocessor interrupts the master and the taskresumes. The master then copies the sectorram into its own local memory and the job isdone.

Two interesting points arise from thisexample. The first is the disc access was doneas an eigh`-bit transfer but the memoryaccess was done as a 16 -bit ram -to -ram copy,the point being that the time spent on theVMEbus was very short. The second point isthat it is very likely that the next sectorrequest will follow the previous. This isalready sitting in the disc processor's mem-ory. In this case the next sector read will beextremely fast in fact at 16 -bit memoryspeeds. What we have here is the slave doingsector management.

This may sound simple and obvious but inmany systems the architectures create a


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1/0 t

I/O system withc pu and I/O cards

Figure 5. The i/o slave bus: The i/o is Accessed via a separate i/o bus via bus coupler (eg.from VME to STE). The i/o bus (eg. STEbus) can have its own processor(s), memory and i/ocards. In other designs, the coupler may be incorporated into one (or all) of the masterc.p.u.s and the secondary bus may be manufacturer specific. Unfortunately, suchsolutions are quite expensive, incurring the cost penalties of two backplanes and the buscoupler itself.

severe bus bottleneck by transferring thesectors directly onto the bus, either undermaster control or with d.m.a. transfer. Someeven cause the shut down of all other tasksduring the transfer.

Probably one of the worst architectures,and yet one of the most common, is wherethe execution bus and the data bus are thesame thing. Now the master program execu-tion is slowed down or stopped during a disctransfer.


Another prime area for master/slave efficien-cy is the text processor, which uses adifferent technique for communication tothat of the disc processor. The text processoruses a single -byte data channel with a statusregister to semaphore data movement.Again the activities of the slave are complete-ly asynchronous to that of the master.

Using the example of pRimr "Hello": inconventional systems each letter would beprocessed in turn. With the master/slavearchitecture the whole statement can betransferred in one go. The master can thencontinue executing its program while thetext processor writes "Hello" to the screen.This is analogous to a printer spooler. Infact, the text processor also has a printerspooler of 64Kbyte and a keyboard input.The keyboard processor stores the keystrokes in a local buffer, so providing atype -ahead facility. The master takes the firstkey from the slave buffer, if the buffer isempty, the master can request that the textprocessor interrupt the master when a keycomes in and then suspend its task. The taskrestarts when the next key is pressed.


The simplest area of the computer is prob-ably the most neglected. If the system c.p.u.is running the language in a control applica-tion, there are a number of operations whichcan be performed. The c.p.u. issues com-mands along the VMEbus to the i/o proces-sor in the form

<token>, I <parameter>l<parameter2>l . . .

Because this slave is intelligent, these i/ooperations can be processed locally.

Figure 6. The New Wave Architecture: Each card on the system bus has its own localmicroprocessor and memory. Analogue and digitial i/o is controlled by the i/o processor A.so that most i/o tasks do not require the use of the system bus. The system bus is now a 1.data bus rather than an execution bus.


The first bus systems were produced by the major semiconductor manufacturers and assuch they were a vehicle for the sale of their products. These products were used by systemhouses who found them wanting in some respects and as a result some went into design andmanufacture themselves.

Another group of manufacturers grew out of the add-on market These companiesoriginally developed cards for specific machines by adding extra iio to standard computersystems or PCs. A fourth group grew out of the need of some of the larger companies for largenumbers of cards for in-house use, particularly in testing and plant monitoring.


Digital operationsBit -wise manipulation Immediate:a. define bit as imput or outputb. turn offc. turn ond. invert existing output statee. read external signal level

Real-time events:a. positive edge detectb. negative edge detect.

2. Byte controlImmediate:

a. output byte (write)h. input byte (read).

B. Analogue operationsUsing a 12 -hit. 12µs analogue -to -digital


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converter and a 12 -bit digital -to -analogueconverter

Immediate:a. read input a.d.c. channelb. write output d.a.c. channelc. read back samples.

Real-time events:a. analogue input greater than defined


b. analogue input less than defined limitc. sampling inputs over time

C. Intelligent operationsa. stepper motor controlb. linearization of transducersc. three -term control loops

D. Local i/o programsThese are completely independent i/o con-trol activities. The master can just set

parameters and monitor the activity. Theslave can interrupt for emergencies.


Returning to the architecture the final prob-lem associated with i/o processing is con-necting the physical devices in question, tothe i/o cards, cards generally use t.t.l.-compatible inputs and outputs with 0-10Vor ±5V analogue inputs and outputs. Thedevices, particularly power, tend to be physi-

- . ,A .,1 040,011111- . _ '

U. . tk..l.1 d..h.0 r

The New Nave Architecture showing a68000 c.p.u. i/o processor and signalconditioning modules.

cally large so that any one single height cardis restricted to eight or possibly 16 channels.

It would be silly to put a slave processor incharge of eight relays even though proces-sors now cost less than relays. A bettersolution is to construct separate i/o busesusing low-cost ribbon cable. One for say32 -digital lines and a second for 32 analoguelines. These cables could then plug in up tofour conditioning cards apiece. This schemeis actually bus -independent and as such iteliminates the need for couplers to providean eight -bit i/o subsystem to the 16 -bit VME.One i/o processor would then be in charge of32 digital and 32 analogue lines and anon -board extension gives an extra 32 digitaland 32 analogue channels. Extensions to thei/o capability of the system could be made byparalleling i/o processors on the bus.

At first glance these new generation cardsdo not look any different from their contem-poraries except for the single -height or 3Uform factor. (VME cards are more usuallydouble -height or 6U.) However, anothertechnique has been used to include theadditional features. Looking at the under-side of the cards, one sees all of the digitallogic is surface mounted. The ability to keep

the size to single -height significantly re-duces the overall system cost.

Furthermore, the i/o scheme described isactually an industry standard, bus -independent scheme that has been im-plemented in the UK in both eight -bit STEsystems as well as the PSI VME system.Taken as a whole, the new wave architectureremoves the need for 'drone' cards such asVME-STE couplers, since the low-cost i/o isnow accessible from the VMEbus.


The new wave architecture removes busbottlenecks of its predecessors withoutadding much to the overall cost. There is onefurther important advantage to the systemdesigner. Because the slave processors areintelligent, all of the system software relat-ing to that card is on -board. This saves thesoftware designer a tremendous amount oftime in installing the final system. Not onlythat, the slaves are processor -independentworking for a high level command/datastructure. This on -board software satisfies95% of all requirements, but to cater for theminority 5% a down -loader can be added tothe system so that system designers canwrite their own slave software.

David Hunt and Keith Hodson recentlyfounded PSI Systems of Cambridge.


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Power RequirementVideo InputAudio InputF M Sound Sub CarrierModulationI F VisionI F SoundSound Pre EmphasisRipple on I F Saw FinerOutput any channel 47 860MHHVision to Sound Power RatioIntermodulationSpurious Harmonic Output


240V 8 Watt (available In other voltages)I V Pk PI 75 Ohm8V 600 Ohm

6MH: lavarlable 5 5MHz/Negative38 9MHz31 9M134 lavadable 33.4MHz I50us6d8 608nW 12mV1 75 Ohm5 to 1

Equal or less than 60dB40dB 18048 if fitted with TCFL1 Filter or corn

bawd via TCFL4 Combiner Leveller

CCIR 3 1 Specification as above but output level 60dBmV1000MV


CHANNEL COMBINER/FILTER/LEVELLERto combine outputs of modulators


2 Channel Fillet Combiner. Leveller. Insertion Loss 3.5d84 Channel Filter Combiner/Leveller Insertion Loss 3 5dBEnables up to 4 TCFL2 or TCFL4 to be combined.





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Mobile radio updateDeregulation and the prospect of spectrum auctions were

among the topics aired by the Mobile Radio Users' Associationat its 1987 conference in Oxford.

with delicate timing, the Departmentot Trade published its consultants'report on deregulating the radio

spectrum just a few days before the confer-ence began, ensuring that no-one therewould run short of a topic of conversation.Copies of the fat yellow volume, the YellowPeril as it was soon dubbed, were on sale atthe conference office in Keble College andquickly became as much a part of delegates'hand -baggage as the inevitable cellular tele-phone.

Some of the background to the report wasreviewed in the first session by Tony Niedus-zynski, head of the DTI's Radiocommunica-(ions Division as it is now called. He listedsteps towards deregulation already taken byhis department: the UK frequency alloca-tions table had for the first time beenpublished (and a reprint was now on theway): non -governmental laboratories wereto be appointed for type -approval testing ofradio equipment. giving manufacturers andimporters a choice of testing house (thoughapproval certificates would continue to beissued by the DTI): low -power satellite tvreception had been legalized for those whohad the necessary £10 licence (and indeedthe DTI did not for its own regulatorypurposes wish to keep any control overreceive -only users).

On the fixed links side. RD had lifted itsrule by which assignments were refusedunless the applicant could show that hisneeds could not be met by the publictelephone networks. For some fixed services.RD was even thinking of offering remoteon-line access to its database and assign-ment software: this would enable prospec-tive users to try out different scenarios to seewhich best suited their needs.

Looking ahead towards the concept ofprivate -sector frequency planning organiza-tions (FPOs) proposed by the consultants.Mr Nieduszynski spoke of moves alreadymade in that direction. "We have increasing-ly sought and used opportunities to delegatemanagement of blocks of frequencies toidentifiable groups of users," he said.

For several years, frequencies for on -sitepagers had been successfully managed by theRadio Paging Association. And very shortly,the BBC and the independent broadcastingcontractors would be assigned jointly a poolof frequencies for their ancillary services.Day-to-day management of this would becontrolled by the broadcasters themselvesthrough what would effectively be a user -FPO. Independent programme makers couldexpect to benefit from similar arrangements


Deregulation of the Radio Spectrum in the UK s the title of the report commissioned by theDepartment of Trade and Industry in 1985 from the consultancy firm CSP International.This document examines the potential for relaxing the rules governing the radio spectrum,for transferring spectrum management to the private sector and for using market forces toensure the economically efficient use of radio frequencies.

All civil uses of radio in the UK are covered by the report, but the authors haveconcentrated on the commercially valuable ranges between 30MHz and 30GHz.

Among the report's main recommendations are the following: For substantial portions of the spectrum, the present licences should be replaced by aSpectrum Management Licence. Under this system, private -sector Frequency PlanningOrganizations would sublicense spectrum to those who required it (other than to broadcastor telecommunications operators. who would need separate government authorization).British Telecom and Mercury Communications would be given the status of Major Usersand would act as their own FPOs. Any potential user should have a choice of at least twoFPOs to approach. Bands should be considered for early transfer to the new system where the number ofindividual licensees is very large, where the band is vacant or soon to become so (e.g. BandIII). or where the present occupants have spare frequencies which they could usefullysublicense on commercial terms. FPOs and Major Users should be free to determine their range of services and chargingstructure. Spectrum Management Licensees might propose new technical specifications oralterations of existing ones. The DTI would refuse these only if they would causeinternational difficulties or unacceptable interference to other users' allotments. Fixed services bands between 1GHz and 30GHz should be managed by two FPOs and thetwo public telecommunications operators. BT and Mercury. Private mobile radio bands should be managed by four FPOs plus the Joint RadioCommittee (which accounts for some 43 000 mobile units in the gas, electricity and coalindustry) as a Major User. Each would have both v.h.f. and u.h.f. allocations. SMLs should be licensed in the sound broadcasting area. in accordance with the recentGreen Paper. Bands for exclusive satellite use should continue to be managed by the DTI. Thedevelopment of small -dish business satellite services in these bands should be encouraged. Responsibility for monitoring and enforcement should be divided between the SMLs andthe DTI's Radiocommunication Division. Amateur radio allocations should continue to enjoy a degree of protection, but the UKgovernment should apply pressure in international discussions to avoid increasing theseallocations or even to reduce them.

The consultants estimate the annual economic benefit of a 1MHz portion of u.h.f.spectrum at £75000 for fixed services, £1M to 4.6M for mobile services and £4M fortelevision broadcasting. Radio paging, with its capacity for extensive re -use of frequencies,rates much higher. These figures, they believe, indicate the advantages to the economy of are -allocation of spectrum.

Deregulation of the Radio Spectrum in the UK is published by Her Majesty's StationeryOffice at £9.50. The body of the report consists of 182 pages and there are six appendicescovering cost analyses, capacity requirements, a summary of spectrum allocationprocedures in the United States. and a review of literature.

Comments on the report should be sent to the Spectrum Pricing Secretariat, Room 305.Waterloo Bridge House. Waterloo Road. London SE1 8UA.

a little later; and discussions were in prog-ress with other user groups, including thewater authorities, local government and theLondon courier companies.

For existing licensees, policies were beingapplied much more flexibly to take accountof local circ*mstances: for example. facili-ties such as talk -through and reverse -frequency working were being granted.

A major piece of deregulation soon to takeeffect would be the exemption from licens-

ing of a wide range of low -power devices.including radio microphones, garage dooropeners, toys, security alarms, baby alarms.and alarms for the elderly. Some 25 000existing licences would be swept away by themeasure, which was to cover the inductionbands, telemetry and telecommand bands.including 49MHz. Also exempt would hewidehand alarms on 48MHz: the DTI hopedthat this deregulated slot would provide anopportunity for British industry to flourish.


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Several times Mr Nieduszynski returned tothe theme of creating opportunities. It wasthis principle, he said, which lay behind hisdepartment's thinking in looking at dereg-ulation and market forces: if the aim was toraise revenue for the Treasury or to cast offthe Department's own responsibilities, hehad not been made aware of it.

The question was how to increase oppor-tunities substantially without doubling RD'sstaff. And he reviewed some of the ways inwhich the current licensing system fell shortof perfection.

One failing centres on the operator who isinefficiently using spectrum which is in highdemand by others. He has no incentive atpresent to do other than use the cheapestand possibly most spectrum -inefficientequipment, since he gains nothing by relin-quishing frequencies. He cannot sell orsub -license unwanted spectrum. And if helets Waterloo Bridge House hear of hisposition, he risks forfeiting the frequencieswithout compensation. The licensing autho-rity could require him to buy more efficientequipment: but it had no meary of judginghow much extra cost the scarcity of spec-trum warranted.

Other problems for RD included difficultyit had in judging which of its queue ofapplicants offer the schemes with the bestchance of economic or commercial success;and the lack of incentive at present forseeking new ways of exploiting the spec-trum. Most people expected to be told thatno spectrum was available. And the user whohad been given frequencies for one purposebut wanted to use them for somethingdifferent risked losing them to someone else.

Mr Nieduszynski outlined possible ways ofreducing this rigidity, many of which werediscussed in CSP International's report.

One approach designed to increase ex-ploitation of the spectrum was to license twoor more franchisees to exploit the same pieceof spectrum, as is the case in the USA withfixed links. The user would then have thechoice of organizations able to provide himwith his assignment.

Another approach, requiring the use ofnew technology, was the currently -proposedPrivate Advanced Radio System (PARS).With this, many users could have access tothe same spectrum without interference: theequipment itself would select a free channel,and no user would have a pre-emptive rightto any particular frequency.

Later on, it might be possible to do awaywith all controls on certain bands (60GHz,for example) where it was unlikely that userswould cause interference to each other.

But Mr Niedusynski reminded delegatesthat the report did not necessarily anticipatefuture policy: the Government had an openmind on these issues. It had asked to receiveviews and comments by 30 June.


To start off the debate, the conferenceorganizers had arranged three presentationsto set out the pros and cons of deregulation.

First came Michael Kennedy from Motor-

ola Inc. of the USA, to give a picture of life ina deregulating environment. A .series ofFederal decisions since the 1970s hadbrought a considerable degree of privatesector control to mobile radio and hadproved very successful, he said.

Frequency co-ordinators designated foreach service handled most of the administra-tive routine in issuing licences. They proces-sed each application, dealt with technicaland other issues and were allowed to chargereasonable fees. Since co-ordinators wereresponsible for post -licensing problemssuch as interference, they had an incentiveto get things right first time.

Matters of overall policy were still dealtwith by the Federal Communications Com-mission, which continued to represent theUS's international obligations to the ITU.

There were now some 9M private trans-mitters in the US, said Mr Kennedy, andderegulation had created a very healthyclimate. It had brought more services forbusiness, especially in the fields of data andpaging, lower costs, technical innovationand many direct and indirect public benefits.

A controversial proposal now before Con-gress was for frequency auctions. Radiousers would file their licence applications inthe normal way, but the fees would bedetermined by the auction. An annual re-venue for the government of some £350Mwas though possible, and Congress wasnaturally interested. Public safety services,radio amateurs and mass media were ex-cluded from the proposal, though some feltthat tv stations ought not to be.

Motorola's fear was that auctions couldinhibit the introduction of new technology;if frequencies began changing hands .veryrapidly, future planning would become veryuncertain.


Arguing the case for central control of thespectrum was Jorma Karjalainen of theFinnish PTT's radio department; though headmitted (to laughter) that some of the areasnow being deregulated in the US had neverbeen subject to regulation in Finland.through lack of regulatory manpower.

The spectrum was a limited natural re-source, he said. Central control offered theadvantages of consistency of policy, econo-mies of scale important to a small country,concentration of scarce expert resources,and the ability to maintain up-to-date know-ledge of spectrum usage for forecastingfuture trends.

Summing up the arguments, John Car-rington of British Telecom Mobile Com-munications said he believed the regulationissue was a bit of a red herring. The propo-nents of both viewpoints were moving to-wards flexibility and the accommodation ofnew technologies.

Under the proposed system, he said, theidea was that RD would withdraw to a role ofrepresenting the UK at international foraand ensuring that FPOs' allocations com-plied with international regulations.

But it would presumably be necessary togive each FPO an allocation in each band;and for two FPOs, the inefficiencies this

would create might be an acceptable over-head. However, as the number of FPOsincreased, this overhead would quickly be-come dominant. "By opting for spectrumpricing as well as deregulation", he said,"one is not so much throwing out the babywith the bathwater as selling the bath withthe baby in it." A flexible approach thatencouraged redeployment of frequencies,rather than a free-for-all, was what hewanted.

British Telecom, as a major spectrumuser, is an obvious FPO candidate; and aquestioner afterwards asked Mr Carringtonwhether his company could be sufficientlydisinterested to act as an FPO on behalf ofothers. If there were two FPOs of equalstature, Carrington replied, effective com-petition would arise. Pressed by anotherspeaker who wanted to know whether BTmight turn away applications which mightharm its own business, Carrington said thatsuch worries could be ignored: colleagues inBT saw it as against their own interests to actin such a way. Another voice commentedthat spectrum pricing would not encouragebetter use because BT could afford to payhigh rates. John Carrington replied that ifpockets were deep enough the spectrumcould be sterilized, and this was one of thepitfalls of deregulation. But BT had alreadydiscussed certain areas of spectrum which itcould release for others to use.

In a later open -forum discussion, MikeCoolican of RD was asked about the reduc-tion in strength of the Radio InvestigationService proposed by the report, since manyusers might expect interference to growrather than diminish. Coolican said thereport envisaged that each FPO would lookafter its own patch of ground. Unless Parlia-ment gave FPOs policing powers, decisionswould be enforced by contract law as in theUS; though this, he added, could become alawyers' charter. Otherwise, RIS would haveto get whatever strength was needed.

The impression given during coffee -

breaks was that many delegates thoughtCSPI's package of proposals unpractical intheir present form: the report might bestrong on philosophy but the technicalissues affecting mobile radio had not beenthought through. A worry expressed by oneradio network operator concerned how in-terference problems might be resolved. Atpresent, frequency conflicts can be dealtwith quite simply by moving a channel ortwo following discussions with RD. But ifrival FPOs were involved, each might blamethe other and nothing would be done.


Mobile radio's other hot topic of the momentis Band III radio, for which spectrum re-leased by the closure of the v.h.f. televisionservices is being reallocated. Martin Cain ofRD's frequency planning unit outlined someof the difficulties with this band, whichcertainly sounds a nightmare. Since tvbroadcasting continues to occupy Band IIIboth in Ireland and in continental Europe,interference must be strictly controlled.Protection criteria have been agreed withthe administration in France, Belgium and


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the Netherlands and RD must observe themto the letter.

So far, the planners' activities have con-centrated on the middle sub -band, with basetransmitters in the range 200-208MHz andmobiles on 192-200MHz.

A formula drawn up by the CCIR is usedfor calculating the total nuisance field due tothe proposed UK stations; and it is possibleto reach the agreed limit on a given channelwith a single well -sited station in southernEngland. Because of the need to minimizeinterference around the vision carrier fre-quencies of the continental tv channels,some frequencies are no-go areas; othersnear the sound and colour subcarriers arevirtually so.

With regard to Ireland, the difficulties arealmost worse. Mr Cain said that the broad-casting authority there had regarded theUK's intentions with deep suspicion. It hadbeen talking of co-ordination radii of 700km,which would impose severe restrictions onthose areas of the UK not already subject tothe agreements with France and the LowCountries.

A further worry is the prospect of second -harmonic interference from Band II broad-casting. There is little reason to suppose thatthe many unlicensed stations lose muchsleep over this aspect of their operations.

One man who will have to cope with allthese difficulties is Alan Sheward, who pre-sented an update on GEC's national Band IIIp.m.r. network, due to open for business inAugust. The system - now named GECNational One - would offer a wide range ofvoice and data services, includingdispatcher -controlled or two-party calls, pu-blic telephone and p.a.b.x link -ups, voicemessaging, store -and -forward messagingand vehicle tracking. With its simplifiedlicensing formalities, the network would beresponsive to users; and the common signal-ling standard for all Band III systems wouldmean a wide range of off -the -shelf equip-ment. Dealings with individual customerswould be through third -party service provi-ders, except in a very few cases which wouldrequire special permission from Oftel.

Some of the practical features of trunkedBand III systems were discussed by MichaelVadon, formerly of BT and now a director ofRT Radiotelephones, the regional Band IIIlicensee for north-east England. From theuser's point of view, he explained, the readyavailability of Band III systems would be abig advantage. There would be no searchingfor base station sites, no waiting for equip-ment or for licences to come through - andso customers would buy before the whimpassed. But a drawback would be higherequipment prices than for ordinary p.m.r.:the sets were more complicated and noworld market existed for them.


Most present-day mobile radio networks arevoice -only systems; but with the inexorablegrowth of the computer the need for datatransmission is growing rapidly. Systemsincorporating data links are welcomed byplanners because they can usually make amore efficient use of scarce radio channels.

Sweden's new Mobitex system offers effi-cient communication between data sys-tems and mobile terminals (Ericsson).

One such system is Sweden's new Mobitexnetwork, a trunked voice and data dispatchsystem operating in the 80MHz region.Following a two-year trial, Mobitex enteredpublic service last October. The system is tobe marketed worldwide under the nameMRS6000.

The network is co-ordinated via a singlecontrol channel, the same all over Sweden:by exchanging data over this channel, sta-tions may set up a speech call on one of theassociated traffic channels or transfer a datapacket. If system loading is light, packets canbe exchanged on the control channel. Aminimum system would thus consist of justtwo channels: the control channel and oneother.

Some of the trial Mobitex systems weredescribed by Giiran Berntson of EricssonRadio Systems. One is at Gothenburg har-bour, where it has apparently been used togood effect in speeding up cargo handling.When a ship is being unloaded, crane oper-ators key in the number of each container asit emerges. A central computer respondswith details of where the container should beplaced. Also linked in to the network arelorry drivers approaching the port, who giveearly warning of their arrival. The dispatchcentre can now plan their loading anddeparture automatically.

Also using Mobitex are the Swedish postoffice, whose vans now bring on-line postaland banking services to rural areas: and theregional alarm centres, which act as dis-patchers for Sweden's emergency services.Print-outs from the mobile terminals ensurethat personnel can work fast, without mis-takes and in secrecy.

By 1990, the system will be fully expandedwith 150 base stations, 60 area exchangesand 20 interlinked main exchanges.

A large data communications system nowunder development in Britain is that of theAutomobile Association, the country'slargest handler of motoring breakdowns.The AA's new operations centre at Stanmoreis the focus of its activities in the London

areaand has been in use since May, 1986.Graham Warner of the AA described the

new system, which makes use of data ter-minals carried by the area's 500 mobilepatrols. The AA's workload was increasing by10% per year, he said; and if the change todata transmission had not been introduced,the breakdown service would have becomeunable to cope by 1990. With the supersededradiotelephone system, London patrolsoften took as long as 15 minutes to contactthe base station. Only five radio channelswere available and each radio operatorhandled 35-40 mobiles.

Today, breakdown calls from AA membersare received at Stanmore by an operator whocan quickly locate each incident with thehelp of a computer -based gazetteer. Thisstores not only street names but names ofbuildings and other places of interest -including public houses, together with theirnicknames. Such information makes itpossible to cut out time -wasting 'no trace'jobs. The system now estimates how long itwill take help to reach the stranded motoristand co-ordinates the rescue operation.

Control positions are manned by twooperators, each with an interactive screencapable of displaying job details and statusinformation in 50 different screen formats.

Data communication at 1200 baud hasproved reliable in London, even where therehas been difficulty with voice. The systemuses just four of the AA's radio channels.

A second control centre at Thatcham is tobecome operational in October; and by 1990a network of 10 centres will extend coverageto the whole of the UK. The AA is nowlooking for terminals with improved facili-ties and price -performance for the remain-der of its 3000 -vehicle fleet.


Alan Dick of the Electricity Council providedan update on the teleswitching system2 bywhich a data signal on the BBC's long -wavetransmissions is used to help trim electricitydemand to match the generated output. Thesystem, which since the meeting hasbrought the Electricity Council and the BBCa joint Queen's Award for Industry, is now


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being used by most area electricity boards toreplace clockwork switches for off-peaksupply meters. A new application is in'budget warmth' schemes, by which domes-tic customers can buy electric storage heat-ing in return for a fixed weekly payment. Theoperating board uses weather forecasts todecide how much charge to provide andbroadcasts teleswi tch ing messages daily.

Now being developed in co-operation withMullard Ltd is a new metering device withcommunications facilities - the EnergyManagement Unit or Emu. This can be reador re -programmed via a hand-held unit orremotely over telephone lines. Tariff andswitching information can also be broadcastto it by one-way radio. Emus can handle upto six charging rates, allowing time -of -dayand seasonal multi -rate tariffs. Securitycodes are used to prevent tampering. For theforthcoming trials, the system will be

controlled from the area board's office by adesk -top PC, which will also act as aninterface to the accounting computer.

The trials form part of a European projectaimed, among other things, at showingwhether customers can be coaxed by specialtariffs into modifying their pattern of con-sumption and so reducing overall energycosts. Besides the 850 Emus to be installedin Britain, a further 150 will be in Brusselswhere they will be controlled over a cable INnetwork.

Another remote -metering idea under In-vestigation was to fit electricity meters witha radio device which would enable them tobe interrogated and read by equipment in anearby van. The customer's wiring andservice cable would act as the device'santenna. Trials have already been conductedin the US on a 900MHz version, by the LongIsland Light and Power Company; thoughMr Dick believed that a frequency in therange 1-3MHz would be more practical. Butwould the DTI be willing to allocate one? Asingle 8kHz channel would be sufficient forthe whole industry.

The cost of reading meters worked out at80p-12 per year, and any electronic systemwould have to match this target.


Steve Temple, another member of the RD'steam, turned the spotlight on the future ofmobile radio, where international develop-ments may bring big changes over the nextdecade.

Planners, he said, had to think of theindustry's needs ten years ahead, since ex-perience showed that it took this time fornew schemes (such as cellular radio) toreach fruition. Users should get togethernow with the DTI to ensure that prepara-tions were made. Another mobile radioWARC would be needed around 1992.

Cellular radio in Britain had been a spec-tacular success, with more mobiles in ser-vice than anywhere else in Europe: 90 000new users were joining each year, comparedwith 22 000 in Germany.

For the future, European heads of statehad agreed in December that there should bea common standard for a future cellularsystem and there had been a directive from

Gasmeter EMU.44

_ _ _ Including

_ _ electricitymeter and

Water radiometer receiver

CustomerDisplay Unit


Prototype Energy Management Unit, orEmu. The customer's installation can belinked to an extensive communicationssystem controlled by the area board.

Brussels to keep channels available.There was complete unanimity in Europe

that a narrow -band t.d.m.a. system was thebest technical solution. Thirteen adminis-trations felt able to go forward with thissystem for 1991 implementation date, withonly two (France and West Germany) hold-ing back. [Since the meeting, those coun-tries have agreed to support a modifiedspecification containing features of theirown proposals.] At least three large Euro-pean markets would have to be available in1991 for the system to be a success; but UKmanufacturers would have a chance to be-come world -class contributors to it.


Other centres of activity for planners in-cluded a new European radiopaging systemfor the mid -1990s and a so-called aero-nautical public correspondence service. Thislast would give businessmen global com-




munications by portable telephone whereverthey went. Satellites like those of Inmarsatwould handle in-flight calls, though directground links for the heavily -populated Euro-pean area might be cheaper. Mr Temple,whose hotel in Brussels had just chargedhim £70 for putting through a brief call toFlorida, evidently felt strongly about this.

The introduction of satellite systems forglobal mobile radio is not as far off as it maysound, as delegates heard in a presentationby John Norbury, head of the radio commu-nications research unit at the RutherfordAppleton Laboratory. Interest in the idea, hesaid, had been stimulated by the ATS-6project of 1974, with its 860MHz communi-cation transponder.

Later experiments with geostationarysatellites - such as the Canadian M -Satproject - had been encouraging, but thisclass of orbit brought a considerable costpenalty for countries at moderate latitudes.To avoid the need for a tracking system,mobiles had to use omnidirectional anten-nas; and in North America a 15dB marginover the free -space signal loss had beenfound necessary because of the satellite's lowelevation. A much greater margin would beneeded in cities. Link margin for satellitesystems was expensive: one rule of thumbreckoned it at 11M per dB.

An alternative scheme, with which thespeaker had been involved, was for a systemusing an inclined Molniya-type ellipticalorbit: such a satellite would appear to hangoverhead for perhaps 8-12 hours at a time,avoiding the problem of blockage by build-ings. With a constellation of three satellites a24 -hour service could be provided.

References1. Trunked mobile radio in Band III, by P. J.Delow: Electronics & Wireless World December1986, page 51.2. Broadcast radio -data, by D. T. Wright and S. M.Edwardson: Electronics & Wireless World Novem-ber 1986, page 63.

Conference papers are available from the Mobile RadioUsers' Association at £25 a set. The association's newaddress is 28 Nottingham Place, London W1M 3FD. Tel.01-400 1518.


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ICF7600Dtest signalsfor v.h.f.receivers

Sony's ICF7600D is a handheldbroadcast receiver with synthe-sized shortwave tuning underthe control of a dedicated micro-computer. Here's how the localoscillator signal and its harmo-nic can be used as an accuratecalibration source for two andfour -metre receivers without anydirect connection.

The 1CF7600D uses a variablefirst local oscillator operatingabove the selected frequency andthis is provided by the synthe-sizer with considerable preci-sion. Suppose that you wish toconfirm that a two -metre receiv-er is tuned to channel S20(145.5MHz). Switch on theICF7600D receiver and select16.905MHz. Hold the ICF7600Dclose to the antenna. Thesquelch should lift and a strongc.w. signal should be indicated.

This is because the secondharmonic of the I.o. falls withinS20. Table one shows some of theS channels and their correspond-ing settings.

Two -metre channel AM setting

S14 16.830S15 16.840S16 16.855S17 16.865S18 16.880S19 16.890S20 16.905S21 16.915S22 16.930S23 16.940

Formula one enables a frequencyand its setting on the ICF7600Dto be calculated. Errors canoccur since the test signals variesin 10kHz steps whereas the Schannels are in 25kHz steps.However any variation in theICF7600D will cause the testsignal to favour either the odd -numbered S channels or theeven -numbered S channels. Thismay in turn be checked against atwo -metre repeater output.

The five -line program enablesa microcomputer to calculatethe corresponding a.m. settingsbetween 112 and 171MHz. Thisallows marine band and air -bandreceivers to be checked.

FFEEDBACK;10 DEF FN F(X) = X/2 - 55.84520 PRINT Frequency'.

" ICF7600D " : PRINT30 INPUT " Enter Frequency

MHz " ; f40 PRINT f , FN F If)

50 GO TO 30

a.m. setting = 1/2 - 55.845 (1)

In the case of four -metre receiv-ers the fundamental I.o. is used.This enables 5kHz steps to bemade and the formula for obtain-ing the a.m. setting becomes

a.m. setting = f - 55.845. (2)

The procedure for four -metretests is otherwise indentical, forexample, the ICF7600D would beset to 14.415MHz a.m. to cali-brate 70.26MHz.

Other settings correspondingto frequencies from 56 to 76 MHzcan be obtained.

This unusual application ofthe ICF7600D has been of greathelp for setting up receivers andconverters in the absence oftransmissions. The reader is leftto work out how a 70cm receivertest signal can he generated.Mike MucklowStony StratfordBucks

Betrayal ofscience by

`modern physics'We can classify discipline as

ranging from hard to soft: fromphysics, engineering, chemistry,biology: through sociology.psychology: to geography, his-tory, literature, religion. Thehard disciplines are described as'science'.

In a soft discipline. a model,theory or fact is still of value evenif it is imperfect, flawed.

The definition of a hard scien-ce could be that it is capable ofsustaining a perfect, true, model.theory or fact.

For prestige reasons, the softsciences - sociology and psycho-logy - try to take on the mantle ofthe hard sciences by using 'scien-tific method': a method of arriv-ing at rigid, 'true', facts, modelsand theories. They do this inorder to gain access to the pre-stige and funding (NASA -type)that the hard sciences command.So we see subjects trying to moveto the left, from soft to hard.

Unknown to the soft sciencecareerists, struggling towardsthe left, the position of theircolleagues at the hard, physicsend is uncomfortable. This isbecause if a theory can be exactlytrue, it is also brittle: morevulnerable to complete overturnby new developments than is asofter, imperfect theory. Nowcareer advancement is, if any-thing, a soft subject, not a hardone. So for career reasons, atraitor group in physics has de-veloped a soft discipline called'modern physics'. These career-ists betray science by softeningtheir discipline and so stablizingthe theoretical status quo andwith it their career status quo.

An individual's career in hardscience is brittle, because it is

based on more absolute, there-fore more brittle, theories andmodels. He then makes his posi-tion more pliable. and his statusand career more secure, bysoftening the brittleness of hisdiscipline. In doing this he be-trays his discipline in order toprotect and further his career.

'Modern physics'. a bastardpseudo -physics, is a soft disci-pline which has been developedby career physicists unwilling torisk a brittle career in hard sci-ence.

Meanwhile, the soft sciences(sociology and psychology)trying to obtain the prestige andfunding of the hard sciences arenot fearful of this brittleness. Inany case 'modern physicists' aretelling them that physics is soft.

The sign posts on the roadfrom physics to modern physics- from hard science to soft- are:uncertainty: (wave -particle)dualism: confusion of observerwith observed: relativity: and theuse of statistics and probability.Paradoxically, one of these, sta-tistics, also signposts the oppo-site march of the soft sciencestowards the hard.Ivor CattSt Albans


stabilizationIn the good old days a filamentbulb or an n.t.c. resistor wasused for amplitude stabilizationin Wien Bridge and phase shiftoscillators. However, the output

amplitude, though stable, wasoften unpredictable and tendedto change with ambient temper-ature. These days. active controlcircuits using fets, o.t.as or otheranalogue control circuits aregenerally employed. The majorsource of distortion in these typeof oscillators is the non -linearityin the gain -control element (be itfilament or fet).

This is well-known, but thereis another factor that is generallyoverlooked. The output of thesinewave generator is rectifiedand smoothed by a low-pass filterbefore being fed to the activecontrol element. Now even if thegain control element was per-fectly linear, there would be asecondary source of non -linearity since the a.g.c. biasvoltage is not purely d.c. as itshould be but contains traces ofthe oscillation frequency itself.The conventional remedy is tomake the a.g.c. time constant aslarge as possible, but this is notthe best solution.

Theoretically, it seemed, therewas no way in which the controlvoltage could be made purely d.c.without an excessively long timeconstant. I was pondering overthis problem for a long timewhen the identity sin2x + cos -x= 1 occurred to me.

If we take the two outputs of aphase -shift oscillator that are 90°out of phase, full -wave rectifythem, feed them independentlyinto voltage squarers, and addthe resultant waveforms, we geta direct voltage proportional tothe amplitude of the sinewavesbut having no a.c. componentsin it.

Of course, this method isn'tvery elegant as analogue squar-ing chips are not exactly cheap,but it is certainly worth trying. Iam not aware whether any ofyour readers have thought of thisidea which I feel is the solution tothis problem.K. ShankarMadrasIndio

New marketsI read with interest the editorialin the April edition discussingnew markets for the UK electron-ics industry. I would like tosuggest another region whereUK and Japanese companies mayhe able to find new markets.

The countries of Latin Amer -


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ica have historically traded withthe United States. but in many ofthese countries governments areemerging which seek greater in-dependence from the USA andare trying to reduce their tech-nological dependence on theUSA. Nowhere is this more truethan in the Central Americancountry of Nicaragua. whichfinds itself embargoed by the USand has turned to Europeancountries, the EEC and the Com-econ nations for new tradingpartners.

I am about to go as a Britishvolunteer to Nicaraga, to teachdigital electronics and micro-processors at the National Uni-versity of Engineering. I will beresponsible for establishing anelectronics laboratory at the uni-versity and advising local indus-try. I have over 10 years experi-ence in industry: currently I amthe manager of an electronicslaboratory within Lucas CAV Ltd.

I would like to invite readers toconsider donating equipment tothis university laboratory. Theprimary benefit to companieswould be that Nicaragua's newgeneration of electronics en-gineers would be trained usingtheir equipment. What may beless obvious is that the universityhas some 21 different nationali-ties amongst its staff. a largeproportion of whom are fromother Latin American countries.The university also has visitorsfrom all over the world: particu-larly Western Europe, the Com-econ area, the United States andLatin America. Thus equipmentgiven would be seen and used byan unprecedented variety ofpotential customers.

Any help offered will be asignificant contribution to apoor third world country and willbe genuinely appreciated. I cansupply a detailed list of the equip-ment and components requiredon request (01-743 3111 till theend of June, 01-993 5631 after).Donald Power34A Cowper RoadLondon W3 6PZ


Having followed with amaze-ment the debate about 'capacitorsound' (which can be practicallynullified by using, where un-

FEEDBACKavoidable, high quality electroly-tics correctly biased and suitablybypassed) I should like to recallattention to the subject of 'tran-sistor sound.' which is more no-ticeable. less controversial, andperhaps a more rewarding sub-ject for investigation.

Most of the pundits will haveread M. Hawksford's paper oncharge quantization in bipolardevices, and the recommenda-tions for minimizing the prob-lem. This prompted a closer lookat the extent of the effect: How itcould be calculated for a givenamplifier and, hopefully, re-duced to negligible levels.

A few calculations showed thatcharge quantization is a propertyof small alternating currents andthat it would present problemseven to a perfect current -drivenamplifier. Given that the chargeon the electron is 1.6 x 109coulomb, it is immediately ob-vious that no bipolar amplifiercan resolve a signal smaller than3.2 x 1019A per Hz (i.e. oneelectron per half cycle). At 10kHzthe smallest a.c. that can flow is3.2 x 10 15A. the only conceiv-able waveform of this currentbeing rectangular. This currentrepresents the threshold of fuzzfrom both the logical and auralpoints of view.

For any current -driven ampli-fier (i.e. bipolar input) thesignal -to -fuzz ratio at the inputwill be 20logI1m/3.2 x 10 151 dBor a little more conveniently20log[3.12 x 1014 1,n1 dB. Alter-natively the ultimate signalresolution (u.s.r.) is equal to3.321°0.12 x 10141,n1 bits at10kHz referred to a given inputlevel, lin (A r.m.s.).

For any amplifier it is onlynecessary to calculate the actualcurrent (ignoring external loadresistors etc) flowing into theamplifier at, say, 5cm/s recordedvelocity for phono inputs or 1Voutput for power amplifiers.

For example consider a typicalop -amp phono preamp:

Open -loop gain (10kHz) 6000Open -loop input

resistance 100k12Closed loop gain 10

Cartridge output (5cm/s15mVPreamp output 50mVDifferential input (50mV/

6000) 8.33µVInput current (8.33µV/

1001d2) 8.33 x1011A

(This is the net current flowinginto the amplifier itself. not the

cartridge load resistor.) Thus

s.f.r. = 20log (3.12 x 10" x8.33x1011(i.e. 88.3dB

u.s.r. = 3.321og (3.12 x 1011 x8.33 x 10 11(

i.e. 14.7 bits at 10kHzref. 5cm/s.

Until bipolar input stages areredesigned to allow higher inputcurrents it seems that it will benecessary to use valve or f.e.t.input stages for good signal re-solution.Roger C LowryChristchurchNew Zealand

RelativityProfessor Michael Butterfield(Feedback February 87) believes"that without space which per-mits geometrical shape andmovement, our very existencewould have no meaning". This israther a strong philosophicalpoint of view which implies thatas a priority we must have"space" to begin with so thatthings can happen! Moreover, wehave also assigned to this strangespace many properties so that DrH. Aspden is, therefore, morethan justified to fill it with anether if by doing so the explana-tion of physical phenomena be-comes easier as well as moreinteresting and palatable!

It is not my intention in thisbrief letter to comment on the"Relativity Simplified" articlebut to emphasize that one of themanifestations of matter in theuniverse implies (create) the"idea" of space. Without the pre-sence of matter there is not sucha thing as "void" or "space" andconsequently geometrical shapeand movement is unthinkable.These aspects can only be direct-ly associated with the energy andforces belonging to material ob-jects. Equally, we cannot gobeyond the world of materialobjects to look for an abyss of aninfinite space. We can onlyconsider the existence of a"medium" between any two ob-jects that are acting upon eachother (be it electromagneticallyor gravitationally). We must.therefore. be concerned with thestudy of this limited and finitemedium with respect to theseobjects and avoid at all costextending our system to involvewhat is logically inconvceivableand in the process get lost in a

forest which neither Cod norNature had ever created.

Finally, universal time is farfrom being an outdated New-tonian concept that had to bethrown out of the window like adead corpse before the arrival ofthe respectful Einsteinian worldsystem at the front door. Grantedthat, for the sake of practicalnecessity, we are forced intoaccepting, for example, our ownearth frame of reference to bestationary in the universe (i.e.zero energy level with respect toabsolute motion, this onlyleaves us with a clock that canread local but not universal time(for the simple reason that so farwe are unable to detect, andtherefore correct for, ourmotion with respect to that pointfrom which everything hadstarted). If it is possible to arriveat this "common time" in a fu-ture theory, then we shall be in aposition to do without measur-ing rods, forget about the con-cept of simultaneity as well as thebedside story of the paradox in-volving the far space travellingtwins. I expect many so-calledRelativists would then be onlytoo happy to throw some of theirown cherished and over-protected hypotheses of Ein-steins's Special Relativity out ofthe window as well!M. Zaman Aki IAl-ThubaeyaKuwait

`Computers,language and

logic'I read the article entitled 'Com-puters, language and logic' by A.Medes but could not understandthe purpose. I was unsure whilereading it so when I got to theend, applied the objective test -see if I could summarize what itwas about. I couldn't really writedown anything concrete. Allud-ing to something? Mathematicsof higher degree circuitry? Thisis the sort of thing that I havebeen arguing for to reinstatecausality.

Other than this there wereoccasional patches of compre-hensibility but no overall coher-ence. The logical problem "I am aliar" was dealt with as a feedbackprocess in a logic inverter tosimulate the sequential processin our conscious awareness,


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accepting one idea then theother, then back again.

Is the concept of causality stilltreated with contempt or are youbecoming educated to under-stand your own mental proces-ses: not to have double values, inengineering practice (causalityrules the machine, intuitiveknowledge) and in theoreticalmodelling (causality appears tovanish in asymptotic equilib-rium formulae).

In the example here, it is pre-sumed there is a propagationdelay to explain oscillation, thelogic unable to 'decide' on aconsistent certainty.

How would you explain thetheoretical inconsistency if yourephrase the problem, replacingthe logic gate with an analogueamplifier and used the 'op -amp'formula for negative feedback?

The op -amp formula does notpredict oscillation simply be-cause this intuitive informationis not programmed into its de-rivation which assumes, falsely.that stable equilibrium can existfor the feedback currents.

If causality is assumed withpropagation delay, we use itera-tive analysis, the feedback pro-cess generates a power series ofterms (voltages) which IF it con-verges produces the op amp for-mula as its asymptotic form.

The instability between 0 and1 states does not appear in theop -amp formula which passesthrough the logic value of 1/2 (seemaths textbook 'DivergentSeries' by G. H. Hardy).

The author A. Medes seems tobe struggling for an idea: "Thecalculus of logic can be used todescribe some simple circuits,(no feedback)...but it is totallyinadequate if we require rigorousmathematical description ofother types of circuit". Logic saysnothing about physical reality.Logic is merely a low -noise in-formation storage medium - amedium for storing informationor physical intuition derivedfrom experience.

The required idea is causality.modelled by discrete elementanalysis. Interactions are de-scribed by iterative processeswhich might converge to anasymptotic limit under certainconditions of the feedback in-teraction. The asymptotic limitis called, inappropriately, the'generating function' for thepower series of the iterative pro-cess.

FEEDBACKJustification for the use of the

surd V-1 is: logical self -consistency. It needs no more'meaning' than its definition:when multiplied by itself it gives-1. In all complex formulae thereal and surd elements remainlinearly independent of oneanother because they cannot becombined in arithmetical cal-culations until all surds aretransformed hack to reals again(in some 'real' invarient).

In modelling physical situa-tions j = V-1 arises in asympto-tic formulae (of circular func-tions) when we assume equilib-rium can exist for the amplitudesof sinusoidally varying re-sponses.

The mathematics of complexnumber algebra is neat but hidesa lot of physical assumptions thatmay not necessarily be valid. Sodon't he fooled by superficialitiesof appearance.P1 RatcliffeStevenageflats

Time and spaceI enjoyed reading Scott Murray'sarticle "If you want to know thetime..." but searched in vain forthe rider "ask a relativisticpoliceman". Can it really be thatclocks at the pole and at theequator can cooperate to provethat Einstein was wrong?

Such a proposition is out-rageous and I have it on goodauthority. The editor of PhysicalReview Letters has drawn myattention to an experiment* re-ported by NASA. It appears thatin 1976 the NASA -SAO rocket -borne redshift experimentproved that the theory of relati-vity was correct and that over a10.000km range from the Earthlight speed was the same in oppo-site directions within 3 parts in abillion. If this is true, then, as anantirelativist, I am defeated andScott Murray should hoist thewhite flag as well. No longer canWireless World entertain us byencouraging debate in this excit-ing arena of 'relativity'.

It wold indeed be sad if Wire-less World followed the exampleof Applied Optics. The editor ofthis journal. published by theAmerican Institute of Physics,had occasion to write at page 544of the March 1977 issue: 'It wasprobably unwise for Applied Op-tics ever to have ventured into

the controversial area of relativ-ity theory land the various optic-al tests for it). In that area eventhe experts carry long swordsand enjoy duelling to the death.Unarmed editors of applied jour-nals would be well advised toavoid that battlefield'.

It appears that NASA did senda stable maser oscillator intospace to test relativity. As a clock.it behaved as expected in slowingdown as it returned to the stron-ger gravitational potential in itsdescent. This is just as ScottMurray would predict. But whatabout the time dilation effect dueto motion? Well. since relativityreferences motion on the obser-ver, the speed of the rocket wasreferenced on the Earth frameand the time dilation terms weresmall enough to be ignored. Theexperiment performed by NASAhas such small residual errorthat it could be said with confi-dence that the radio signals sentto the rocket travelled at thesame speed as those sent backfrom the rocket. No evidence ofmotion through the preferredframe was found, and the rangewas 10.000km.

Now. what is fascinating aboutthis experiment is that it was amajor NASA project involvingnumerous scientists and aimedat testing relativity. It was seenas an experiment to detect mo-tion through the ether, besidestesting the effects of gravity. Yet.in the analysis the time dilationwas calculated as referenced onthe Earth frame, whilst the re-sulting equation was used toestimate motion relative to thepreferred frame. Could one reallycredit such an error? When thetime dilation formula is refer-enced on the preferred frame theresulting equation contains noterms which would allow theanisotropy to be tested. Theeffects cancel out completely.making the test completely in-consequential so far as detectingour motion through space is

concerned.Such is the arena of debate on

this question of relativity. TheEstablishment scientist wants tobelieve in relativity and no oneseems to question results whichsupport relativity. All the venomis directed at those who seek thetruth and need convincing.

In conclusion, it is relevant tomention that the so-called timedilation formula has only beentested for atoms and particles

moving at very high speeds,speeds far in excess of any ex-pected motion relative to thepreferred frame. The privilegedrole of the relativistic observerhas not been tested in this con-text.H. AspdenDepartment of ElectricalEngineeringUniversity of Southampton

'Vessot and Levine. Gen. Rel. and Gray..

vol 10 1979 p.1s1


Your issue of March has justarrived here. In it John de Rivazsays (Circuit ideas) that sibilantsare made unpleasant due to over -modulation . That they are oftenunpleasant or exaggerated is

true. but since Wrotham f.m.opened in 1951. I have been ledto believe that this is due to animbalance in the frequency re-sponse of the total overall audiosystem being used. Judicial useof audio equalizers (and not tonecontrols) seems to take care ofmost cases.

Your Dolby -inspired article ondigital audio equipment forbroadcasting in the same issue.with its variable but closely con-trolled variable pre -emphasis.ought to provide the tools tocheck this problem which soworries purists.

By the way, the BBC WorldService broadcasts. althougha.m. with limited audio top end.seem to have their audio soprocessed that voices soundnatural and without undueemphasis of the sibilants. Maybea BBC spokesman would care toexplain how they do this.Peter HirschmannHaifaIsrael

UntOrtunately the BBC's re-sponse did not arrive in time forincloino in this issue.


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jp1 E._ OF'


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Within the last 10 years ILP Electronics has become the largestmanufacturer of toroidal power transformers in the UK.Opposite we are displaying a typical quotation for a custom designtransformer, in the months to come other examples will be shown. Ifyou wish us to quote for an existing transformer or perhaps one forthe future, our CAD assisted design team will be pleased to quote.We have a large standard range from 15VA-625VA with primaries of120/240V which are available ex -stock (up to quantities of 25) from ourdistributor Jaytee Electronic Services, 143 Reculver Road, Beltinge,Herne Bay, Kent CT6 6PL - Telephone: (0227) 375254 - Telex: 295141TXLINK G Quote MBX 022735254.All standard transformers are supplied with a full mounting kitcomprising of 1 metal washer, 2 neoprene washers and nut, bolt +washer. On custom designs a variety of mounting methods areavailable including centre potting, threaded inserts etc.Our design department offers a speedy quotation and prototypedesign service with full engineering support including field calls ifrequired. Our manufacturing range is from 5VA to 5kVA with multipleprimaries and/or secondaries, to U.K. and International standards.Price stability:Our current policy is that prices are fixed for one year commencing1st January 1987.We also have expertise in designing for low acoustic noise, low strayfields and low temperature rise etc.

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Europe's capacitormarket

Whilst the semi-conductor industryworries itself about the

cost of R&D and strategic mer-gers to breech the $1bn billings'critical mass,' the capacitor in-dustry worldwide is facingsimilar issues of profitability andtechnological and businesschange. Over the last two or soyears, many household names in

For many years the somewhat slow moving andmature capacitor industry has been overlooked byinvestment interest and PR pizzaz. But there are

changes afoot, in both market and industry.






ir- Py ri



1082 19e3


W. CAM -

'484 1Per

r`4r4140 r- Fo.,.

F g.l. Percentage share of the total capacitor market enjoyed bythe major dielectric families from 1982 to 1986.

capacitors have declared the desire for amerger with a stronger group. Some haveopenly declared unprofitability followed by

rapid posting of 'For Sale' notices. Only inFrance is there evidence of bullish invest-ment being made to increase manufacturing

capacity of technologies thathave much less than averagegrowth. Elsewhere, it is ex-clusively the ceramics housesthat have been spending money.

The shake up of the industryhas followed a radical shift in thetechnology used by circuit de-signers, as shown in Fig.1. Fromthis illustration it is evident thatthe dielectric flavour of the

month is ceramic - and multilayer ceramicat that. The tantalum, aluminium and filmindustries have lost market share to cera-

Fig.2. Change in packaging of the tantalum capacitor elements Fig.3. During the last three years consumer preference betweennote the rise in popularity of the chip packaging style. paper and film capacitors has been almost static.

Fig.4. Emerging popularity of the chip packaging style in the Fig.5. Since 1984 the package styles of aluminium capacitors haveceramic dielectric is largely at the expense of discs. moved slightly away from the large cans and axials to small cans.


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Fig.6. Smoothed forecast of the likelygrowth of capacitors in Europe to the endof the decade.

mic, which has trebled its share of theEuropean market since 1982. Comparisonwith the US market will show an evenstronger move towards ceramic, since theUS does not have the installed and some-what protected film dielectric manufactur-ing base that is characteristic of Europe.

Figures 2 to 5 show the movements withineach dielectric of the packaging of thedielectric. It should come as no surprise thatthe chip package is becoming popular at theexpense of the traditional parts. The trend tosurface mounting is of course playing havocwith the relative market shares of eachdielectric, since the ceramic capacitor isideally suited to the surface mount assemblyprocess - manufacture of a leaded part startswith a stand-alone chip. The other technolo-gies must add extra manufacturing processsteps to their capacitor element to protect itfrom the harsh soldering environment,shrugged off by the ceramic dielectric,thereby increasing cost. The most at riskfrom the move to SMT is the small alumi-nium and film dielectrics that shy from thesoldering processes used.

Interestingly, the tantalum capacitor isforecast to fare well in this trend to SMTsince no other dielectric can offer thevolumetric efficiency at the cost, so the roleof 'replenisher' or topper up of on -boardcapacitors will remain the domain of tanta-lum, whether leaded or chip. However, themove to SMD in all dielectrics is mostpronounced in ceramic, in particular forconsumer applications.


The capacitor market is forecast to keep ongrowing. The relentless pace of the electro-nics industry is utilising electronics technol-ogy for more applications in all sec-tors. The computers, consumer, com-munications, instrumentation and controlindustries have depended absolutely uponutilisation of electronics, and now newcom-ers, the car industry, are starting to exhibitstrong demand as they embrace electronicstechnology. The defence industry hit, withcutbacks worldwide, are utilising theirsomewhat reduced disbursem*nt in a differ-ent manner. Gone are the projects for biggerguns - they are replaced with more sophisti-cated projects that improve control ofweapons, and improve communications andintelligence, which all need electronics. Sodefence budgets are favouring a very strong





Indek-qi bookiricri

11111111111111111111111111111984 1986 1988 1987 1988 1989 1990












1888 1990

Chramlc M/L P 8 Film

Fig.7. Expected movement of designer prefere-ice for each dielectric as the marketgrows in the coming years. Notice the enormous growth forecast for ceramics.

swing to more electronic equipment. Thecommunications industry too is lifting offwith strong demand for mobile communica-tions: cellular radio is the driving force.

The capacitor element of this growth isforecast to grow about 9-10% in 1987 and alittle more in 1988 - 12-14%. Beyond thatpundits are already speaking of the nextslowing down of demand that hits the elec-tronics industry from time to time as supply.stocks and demand move out of line. Duringthat time, SMD is forecast to grow rapidly byas much as 50% a year and it is clear that thewinners are going to be ceramic and tanta-lum dielectrics. The others will find theirniche which will keep some of the machinesrolling- in many applications the traditionalthrough hole technology remains the opti-mum choke - but it is clear that there are agalaxy of companies, large and small, thatplan to move into surface mount in thecoming year.

In terms of numbers of units, the general -use on -board capacitors dominate total de-mand. They are the most affected by thechange in assembly technology and so mas-sively influence the global numbers. Foroff -board capacitors, the large power correc-tion capacitors, or the large aluminiumcans, the growth pattern is individualistic

and it is misleading to offer a global growthfigure since these capacitors tend to beend -use, application -specific. However, it isclear that in medium power applications,incumbent energy storage capacitors will beeventually replaced with smaller devicesworking at high frequency. The dielectricchosen for this application is most likely tobe ceramic in the medium to long termalthough aluminium will continue to findfavour in the short term. This is because theESR of ceramic at 1MHz is much lower thanaluminium or wet tantalum, and at thesefrequencies the consequential capacitancerequired falls dramatically to a few microfar-ads. Savings can be made not only in termsof microfarads, but also in the size and costof the magnetics which at 1MHz are afraction of those at 50Hz or 40kHz.

We may then refer to Fig 6 & 7 to forecastthe likely future for capacitor demand bydielectric and numbers of units sold. It lookssound for ceramic and not too bad fortantalum, but we trust the manufacturers ofother dielectrics have already selected theirniches.

Keith Thomas is vice-president of sales andmarketing, Europe, forAVX ofNew York.


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Capacitor technologiescompared

Ceramic, plastics film, or electrolytic? With significant overlaps incapacitance value, it is important that design engineers have a good

appreciation of the factors involved - especially in todays cost -sensitive markets.

Every year, as capacitor technologiesimprove and are stretched to newlimits, the complexities and the eco-

nomics of the enormous variety of styles,materials and performance characteristicsbecome more difficult to understand.

Miniaturization, new materials and newproduction techniques have resulted insome radical, and many subtle changes inthe range of capacitors available today.

The majority of capacitors used in electro-nic engineering fall within the spectrum ofone picofarad ( 1 pF) to 220,000 microfarad(0.22F) and are grouped into a number ofmain technologies. They include ceramic -based capacitors, film or plastics types andaluminium/solid aluminium/tantalum capa-citors.

Each of these technologies cover typicalcapacitance values as shown in Fig. 1.

Perhaps the most complex area is theoverlap of ceramic and film technologies forwhich the following comparisons andobservations can be made.


Plastics -film capacitors utilise one of fourmain plastics films for their dielectric mat-erial; each has advantages and disadvantageson performance, stability, dielectricstrength. environmental resistance andcost.

The film dielectric is either stacked, ormore commonly wound with electrodelayers to form a capacitor cell. The electrodelayers may be metal foil or the cell may be anintegral winding of metallized film (theelectrode layer being vacuum deposited ontothe film). This metallized film constructionrealises a very size and cost efficient capaci-tor: it does, however, have a limited pulseload capability (see Table 1). A film/foilconstruction by comparison has significant-ly better power handling (pulse load) capa-city but will be larger and more expensive.

Four main plastics films are used asdielectric material: polyester (PETP) poly -carbonate, polystyrene and polypropylene.Each has its own unique features.

Polyester is by far the most commonlyused material due to its low cost andreasonable performance characteristics.Moderate voltage ratings, pulse load charac-teristics, temperature and frequency stabil-ity all combine to produce the ideal purposecapacitor. The cell is almost always of metal -


Capacitance spectrum per major technology


Wet electrolytic /Solid a.maum/ tantalum

Fig.1. The most cost-effective technology will vary depending on basic capacitance valueand on a multitude of other interactive parameters.

lized film construction and frequently in a5mm lead pitch module for which capaci-tance values up to 1µF can be producedreliably and economically.

Polycarbonate is a higher performancealternative to polyester for general purposeapplications. Capacitors in this materialcommand a price premium (typically +15 to+30%) and offer improved stability ofcapacitance (AC) with changes in tempera-ture and frequency. Maximum voltage rat-ings and pulse load characteristics are alsobetter than those of polyester. The use ofpolycarbonate capacitors in modern circuit-

ry is declining and hence this dielectric isonly offered by a few major manufacturersleg Philips).

Polystyrene is probably the most com-monly used material for precision 1% toler-ance capacitors. Usually in a film/foil con-struction, polystyrene provides optimumstability of capacitance with temperaturechange. The capacitance/temperature rela-tionship is linear with a -125ppm tempera-

Fig.2. Sintered ceramic electrode multi -

layer construction creates a size -efficientand reliable capacitor.

Table 1. Typical pulse load limits in V/p.s for metallized film capacitors (based on pulse voltages equalto the rated dc voltage)

Rated d cvoltage

Lead pitchdielectric.


7.5mm lOmm 15mm 22.5mm 27.5mmMkT MkT MkC MkT MkC MkT MkC MkT MkC

63 55 17 15 6 - 3 - 2100 90 30 24 30 10 13 4 6 3.5 4.5250 60 35 45 14 18 6 8 5 7400 95 55 70 22 30 10 13 8 1

MkT: metallized polyester. MkC: metallized polycarbonate.


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ture coefficient (t.c.) ie - 0.0125% reductionin capacitance per degree of temperatureincrease above 22°C. with capacitance valuescovering typically 10pF to 100,000 pF at±1% tolerance and with the stable andlinear-t.c. polystyrene capacitors are mostfrequently used in applications requiringtemperature compensation, also tuned cir-cuits and filter networks.

Polystyrene is however relatively expen-sive and is significantly limited by its maxi-mum operating temperature of around85°C. As a result polypropylene film/foil isbecoming increasingly important for preci-sion film capacitors. While still offering±1% tolerance on capacitance, a relativelystable t.c. (-125 to -250 ppm), and capaci-tance values approaching 0.1 µF; polypropy-lene meets -40/+100°C environmental re-quirements and is less prone to thermalshock during soldering.

Polypropylene also performs well withhigh voltage and is consequently used inhigh pulse/small power capacitors. Metal-lised or double metallized polypropylenewound with foil can achieve voltage ratingsin excess of 2000V dc and is often an idealchoice for a.c. applications, Polypropylenecapacitors have traditionally been used indeflection circuitry and as flyback capacitorsin tv applications and are now being com-monly used in switch -mode power supplies.

Table 2 summarises some of the charac-teristics of the principle film dielectrics.


Two construction methods are used for themanufacture of ceramic capacitors.

Single -layer types consist of a single rec-tangular or discoidal layer of ceramic mate-rial with a silver or (for higher reliability)copper electrode on each side of the ceramic.Leads are soldered to the electrode layersand the capacitor is protected by a mouldedbody or cost effective lacquered coating.

With multilayer devices very thin (20-25p.m) layers of ceramic interleaved with offsetprecious metal electrode layers are pressedand then sintered at high temperature toform a very compact and volumetricallyefficient monolithic capacitor 'buildingblock'. Leads are soldered to this block orsurface -mounted -type terminations are ap-plied (Fig 2).

Ceramic capacitors are spilt into two main

Table 2. Main plastics film dielectrics -typical parameters.



Tolerance Max.dc



Pulse loadlimit'V/ps




Polyester 1000pF-101.1.F ± 10% 630 Non-linear Typically -55/+100 Low(MkT) ± 20% ." C - 3%

to 4- 7%25 - 50

Polycarbonate 1000pF-100 ± 5% 1000 Non linear Typically -55/+100'(MkC) ± 10% AC < ±2% 30-70

Polypropylene 47pF-62nF ±1% 1000 -125 to High -40/ + 100°(precision) -250ppm


(power)1000pF-1µF ± 5% >2000 -125

to -250ppmVery higheg 2000

-55/ +85

(Kp/mmkp)Polystyrene 10pF-02211F ± 1% 630 - 125pm High -40/+85" High

(kS) ±2.5%

Pulse load limits based on 10mm pitch capacitor for MkT MkC across 100-400V dc rated devices.



at -j o

tt -10t(z -20

Ls, -30


X7R Dielectr,c

NPO Delectni

Z5U Dielectn(

-55 -35 -15 .5 25 45 .65TEMPERATURE (n)

MI5 425+125


4PC013G I



0 5 10 15 20 25 30 35 40 45



tk 10k 100k 1M 10M


Fig.3. NPO dielectric outperform X7R. Z5Uand Y5V but has a limited capacitancerange and is expensive when measuringcost per picrofarad.

classes depending on the type of ceramicmaterial used.

Class I types utilise low K materials whichresult in low losses and stable linear temper-ature dependance.

Class II types have higher losses andnon-linear temperature characteristics; theyare often subdivided into medium K and highK materials.

The three most common 'industry classi-fications' for ceramics are NPO (or COG),X7R and Y5V/Z5U. Cost per microfarad andthe performance characteristics of thesematerials are proportional

Table 3: The relative cost a performance of a filmcapacitor varies depending on which dielectricmaterial is incorporated.

Type Cost Performance(stability of capacitance with

changes in temperature.frequency and voltage)

NPO (COG) Most Bestexpensive


Y5V/ZSU Leastexpensive


NPO devices, and capacitors with a similart.c. (always linear and usually between zero(NPO) and -750 ppm (N7501). fall into theclass I category. Capacitance values rangefrom 1 pF to around 1,000 pF for single layerdevices and up to 10,000 pF for multilayertypes, are typically specified with ± 2% or ±5% tolerance. Class II devices show little orno capacitance change with increases infrequency or voltage and are therefore usedin 'precision' applications in tuning andtiming circuitry.

Class II devices include X7R (medium KIand Y5V/Z5U (high K) types. Both shownon-linear relationships between capaci-tance change with temperature, voltage andfrequency increase, see graphs 1-3. They aresubsequently used in general purpose ap-plications Y5V/Z5U material is most com-monly used for decoupling capacitors whileX7R is frequently interchangeable withpolyester film.


A simple cost comparison of the manydifferent types of capacitor is impossible. Inthe precision area, polystyrene, polypropy-lene and class I ceramic, it is clear that thelatter is most cost-effective for low values upto 1000pF. Between 1000pF and 4700pFprices of ceramic and film are similar whilefor higher capacitance values film capacitorsbecome more cost effective.

In the general purpose area, ceramicsagain are the most economic choice forlower capacitance values (100pF to lOnF).Between lOnF (0.01g) and 0.470 ceramicand film prices are comparable. For highervalues metallized polyester then becomescost effective with metallized polycarbonateproviding a higher performance but moreexpensive alternative.


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Terminations forsurface -mounted multi -

layer chip capacitorsThe choice for terminations for ceramic chip capacitoris between the lower cost of the nickel barrier and the

greater reliability of silver -palladium type

The spread of surface -mount techno-logy beyond the realms of the thick -film hybrid has promoted component

manufacturers to re -assess the materials andtechniques involved in the design and con-struction of surface mounted components.Much of this research is being concentratedon the metallized terminations of ceramicmultilayer chip capacitors.

Unlike leaded, through -hole components,where the mechanical strength of the sol-dered joint is reinforced by the componentlead, the s.m.d. must rely on the quality ofthe soldered joint alone for both electricaland mechanical integrity.

The advent of high-speed placementmachines and improved mass -solderingmethods mean that zero -defect soldering isthe ultimate goal of the equipment manufac-turer who is to capitalise on the cost-effectiveness of surface -mount technology.It is essential that both the solderahility andreliability of the component end -

terminations are at the highest possible levelprior to assembly.

This article discusses the advantages anddisadvantages of the two methods currentlyused in the manufacture of multilayer cera-mic capacitor terminations. Comparisonsare made between silver -palladium termina-tions and those using a nickel harrier be-tween the internal electrode structure andthe outer solderahle layer of termination.Each type is evaluated for wettability duringsoldering. ability to withstand thetemperatures and dwell -times involved inboth wave and reflow soldering, resistance todemetallization at soldering temperatures.ability to maintain a solderable surfaceduring handling and storage under varyingconditions, and cost-effectiveness.

Prior to end -metallization. prefabricatedceramic capacitors are cut to length. fired.and subjected to a tumbling process underprecisely determined conditions. This tumb-ling action rounds off the edges and cornersof the ceramic to enable a subsequent layerof either silver/palladium alloy or pure silverand nickel to he applied evenly over thesurfaces. necessary to help prevent dissollu-tion of the termination by molten solder.


Wettability - Ability of the metal termina-tion to be wetted with molten solder withina specified time without subsequent de -wetting. It depends on the materials usedfor the termination and the level of con-tamination of the surfaces brought aboutby ageing. storage and handling.

Soldering temperatures - The solderingtemperature will depend on the meltingpoint of the solder used in the process,usually between 215 and 235 C for themajority of solders used in the manufac-ture of electrical circuits, but in somecases as high as 260 C.

Dwell time - The time taken for the compo-nent to reach the soldering temperatureand for the solder to flow in the joint areadepends on the thermal demand of thecomponent, which depends on the size.construction, and the materials used.Dwell time varies according to the solder-ing method used, typically five seconds forwave soldering, eight seconds for reflow.and up to 30 seconds for vapour -phasereflow.

Resistance to demetallization - Ability ofthe termination to withstand solderingtemperatures without dissolving. Demetal-lization usually increases with extendeddwell times.

Maintenance of solderability - Wettabilityof the termination surfaces is affected byageing storage, transit, and handling. Mate-rials used for the terminations and themanufacturing process can also effectageing. and hence solderability.


The composition of the silver -palladiumalloy is very important and research hasshown that the correct percentage of palla-dium is vital for the control of both demetall-ization and silver migration. Demetalliza-Lion can cause a build-up of silver con-tamination in the solder bath, giving rise tothe formation of solder bridges on the

finished substrate. This can entail expensiveand time consuming re -work. The migrationof silver across the surface of the capacitor isan on -going problem during its whole life-time. and can cause the degredation, break-down, and ultimate failure of the capacitorin the field. Mullard ceramic chip capacitorterminations contain 35% palladium, morethan in any other brand, which experimentshave shown to be sufficient to prevent silvermigration under all but the most severeconditions (see Table).

Termination Time for Time tocontent first signs of short-circuit

Pd Ag migration (min)(min)

0 1.00 0.5 2.00.11 0.89 0.5 4.50.22 0.78 2.0 8.00.33 0.67 15.00.35 0.65

The silver/palladium alloy, in the form of apaste to which powdered glass is added. ismanufactured 'in-house' under controlledconditions to ensure optimum compositionand rheological properties, and quality con-trol tests are carried out on each batch ofpaste. The paste is applied to the ends of thecapacitor, usually by a controlled dippingmethod, to provide a uniform layer. Thislayer is approximately 35 µm thick on thetop and bottom faces, and 100 p.m on the endface after the capacitor has been fired asecond time to form the alloy.

Wettability of silver and silver alloys is high,arid well -proven in the electronics industry.and under normal conditions of storage andhandling, less prone to oxidation than tin:lead.

Resistance to demetallisation. Class is in-cluded in the alloy to improve adhesion ofthe metallization to the end faces, and also toreduce the rate of dissolution of the termina-tion by molten solder. Exhaustive tests haveshown that Mullard ceramic multilayer chip


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capacitors with silver -palladium termina-tions can withstand the temperatures anddwell times encountered during either wave.reflow or vapour phase soldering withoutany significant demetallization of the ter-minations. However, a small amount ofsilver dissolved into the solder joint beneaththe component is advantageous when thefinished substrate is likely to be subjected tothermal cycling: it renders the joint morecompliant and enables it to compensate forthermal mismatch between the componentand the substrate.

Maintenance of solderability. Regular quali-ty checks, including accelerated ageing teststo determine the effects of air pollution(HS). oxidation in air, and corrosion on thesilver -palladium terminations show thatunder normal storage conditions a high levelof solderability is maintained for up to twoyears. However, under harsh conditionswith a high level of air pollution, storage in acontrolled environment is recommended.


The manufacturing process for the body of acapacitor is the same as that for the silver -palladium type, but after tumblingto round off the corners and edges.the end connections are first formedby applying a controlled amount ofpure silver paste. This provides auniform termination approximately35 pm thick on the top and bottomfaces and 100 Ian on the end facesafter the second firing.

Because silver dissolves rapidlyinto molten solder, a 2 to 3µm layerof nickel is plated onto the silver toprevent dissolution. Unfortunately.nickel is difficult to solder at thecomparatively low temperaturesand low flux activity necessary in themanufacture of electronic circuits.To overcome this, a further 10 to 12p.m layer of either tin or tin/lead isplated onto the nickel to improve itssolderability.

Unlike silver -palladium termina-tions, where the composition of thetermination and that of the capaci-tor electrodes are similar. the nickelbarrier types may be subject to'material transport' whereby puresilver from the base terminationmay diffuse into the silver -palladium of the electrodes. Howev-er, this can be overcome by carefulcontrol of the process parametersduring the second firing.

Unless particular care is taken dur ng theplating processes, conditions may arise thatcould lead to defects during assembly or inthe field: If the chips adhere to one anotherin the plating container, or are not evenlydistributed. the plated layer may not be ofuniform thickness of may even be missingaltogether. If the nickel layer is missing orintermittent, the underlying silver will bedissolved rapidly into the molten solder, sodestroying the termination. A missing orintermittant layer of tin -lead, exposing the

nickel barrier will adversely affect the solder-ability of the termination.

In practice, a layer of tin, to which a verysmall amount of lead may be added to inhibitthe growth of tin 'whiskers', is preferred toeutectic tin -lead. This is because particles ofthe comparatively soft tin -lead may be pro-duced by abrasion during handling, whichunder humid conditions, can cause trackingbetween terminations or between conduc-tors on the substrate.

During firing, microcracks may developin the ceramic body of the capacitor. Ioniccontaminants, inherent in the plating pro-cess, may become trapped in these micro -tracks. These contaminants are very difficultto detect and remove, and because theydissociate into free ions which are goodconductors in humid conditions, may causecircuit failures in the field. They are also

Fig.1. The silver/palladium terminations ofceramic multilayer chip capacitors con-tain 35% palladium and are approximately35 µm thick on the top and bottom faces,and 100p.m on the end faces. The roundedcorners help prevent dissolution duringsoldering.

Resistance to demetallization. The nickelplating is an effective barrier to dissolutionand affords total protection against demetal-lization under even the most aggressivesoldering conditions.

Maintenance of solderability. A solder sur-face of pure tin remains solderable for aconsiderable time. However. there is a

theory that the use of pure tin could give riseto the growth of tin whiskers. causingreliability problems. The addition of a smallamount of lead to the tin. however, inhibitstheir growth. A tin -lead layer has goodsoldering properties when newly made but issusceptible to oxidation in humid condi-tions. so protection from the atmosphere isdesirable.


The important factors to be considered whenchoosing between nickel barrier or silver/palladium terminations are resistance todemetallization, solderability. the reliabilityof both the component and the solderedjoint, and the cost. With normal solderingtemperatures and dwelling times, the resist-ance to demetallization of silver -palladium

is high, and well within acceptablelimits, providing the palladium -to -silver ratio is correct (35Pd:65Ag1and the layer is of uniform thick-ness. This resistance decreasesrapidly as soldering temperaturesand dwell -times rise above normallevels, especially at the cornerswhere the layer may be thinner.

Nickel barrier terminations onthe other hand remain highly resis-tant even under the most aggressiveconditions, providing the manufac-turer employs a high level of qualitycontrol to ensure that the plating isuniformly deposited.

The solderability of both typesremains high under normal storageconditions, whilst in a more aggres-sive environment the solderabilityof silver -palladium or pure tin is

probably better than that of tin -lead.The extra plating processes requiredby the nickel barrier terminations.and the possibility of ionic con-tamination. can cause reliabilityproblems in the finished product.On the other hand, the smallamount of silver that dissolves intothe joint with silver -palladium tendsto strengthen the joint and so im-prove reliability. The present-daycosts of noble metals. especially

palladium, makes the silver -palladium typesmarginally more expensive than the nickelbarrier, even though more processing isrequired for the nickel barrier. With normalmanufacturing processes and optmized stor-age and handling conditions, the decidingcriteria may well be the slightly lower cost ofthe nickel barrier type and the greaterreliability of the silver -palladium.

Fired ceramicdielec nc

Silver / Palladiumtermination



Fired ceramicOuter solderable dielectric


Silver basetermination

Intermediate layer of galvanic nickel


Fig.2. The 2 to 31im intermediate layer ofnickel prevents dissolution of the basetermination during soldering.

highly reactive with metals and producecorrosive ract ions.

Wettability. With effective plating, the wet-tahility of the tin or tin -lead surface is good.better perhaps than silver -palladium, butany thin or void areas, exposing the nickel.greatly reduces the wettability.

This report is drawn from information sub-mitted by Mullard Ltd.


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304.4C/S C300 Racal RA17L Communi-cation Receivers 500KG/S to 30MC/S in 30bands 1MC/S Wide - £175 - All receivers are airtested and calibrated in our workshop -supplied with dust cover - operationinstructions - circuit in fair used conditionRacal Synthesisers (Decade frequencygenerators) MA250 - 1 6MG'S to 31 6 MG/S -£100 MA1350 for use with RA17 receiver -£100.MA259G - precision frequency standard5MC/S - 1MC S 100KHz - £100 to £150. RA137and RA37 - LF convenors 10 to 980KC/S - £40to £75 RA98 SSE-ISB convenor - £50. RA121SSB-ISB convertor - E75 Plessey PR155GSolid State recervers - 60KC/S - 30MC/S - £300.Trenstel Matrix Printers AF11R - 5 levelbaudol code -- up to 300 bauds - for pnnt out onplain teleprinter paper - £50 Army Field

Telephone sets type F L and J - large quani4,in stock - C6 to £15 depending on type altoquantity. P 0 R Don 10 Telephone Cablehalf mile canvas containers - £20 NightViewing Infra -red periscopes - twineyepiece - 24 volt DC supply - £100 EAOriginal cost to Government over E11.000 EAStatic Inverters - 12 or 24 volt input - 240 voltAC sinewave output - vanous wattages P 0 RXV Plotters and pen recorders - venous -P 0 R Signal Generators - various - P 0 RTF 893A - Power meter - £50 Racalfrequency counter type 836 - £50 Tektronicplug -Ins - 1A1 C50 1A2 £40 1A4 £100 M £50All items are bought direct troth H MGovernment being surplus equipment Price isex works S A E for enquines. Phone forappointment for demonstration of any items.also availability or price change V A T andcarriage extra





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rCIRCUIT IDEASCurrent limited 0-200V supplyAn outline in the National Semiconductordata book provided the starting point for this0-200V power supply. Current limitingoccurs at 30mA, set by the 150ft resistor,and load changes up to this point causeoutput variations of at most 0.2V. Since thevalve grid is connected to the output line,load compensation is very fast.

Most of the voltage is dropped by the valve;-only about 20V appears across the 317. Withmy prototype, a short circuit with output setto 200V causes no damage.M. McDermottLondon


Load0 -200V30mAmax

Parallel data multiplexer with RS232 interfaceData on up to 64 digital inputs can besampled and passed through an RS232 orsimilar serial port using simple interfacehardware. A byte is sent to the uart, thelowest three bits of which (receive -data linesRBR1_3) address one of eight 8 -bit ports. Oneclock cycle later DR goes low, resetting theDR flag and loading the uart for transmis-

Data rote clock

sion by pulsing TBRL. Eight bits of data fromthe 74LS373 selected by the decoder arethus transmitted back to the computer.

After 64 clock cycles 4040 output Q5 goeshigh which loads a second byte for transmis-sion by the uart. This second byte echoes theoriginal chip address and the parity errorflag. Hence each time a byte is sent to the



14 21 17 4047k












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uart, two bytes are returned; one containingthe input data and a second for errorchecking.

Details of serial buffers or bit -rate gener-ators are not given as these will depend onyour requirements.G. SullivSnRedditch, Worcester

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(-CIRCUIT IDEASSerial outputA -to -D converterUsing a few c-mos i.c.s data from amultiplexed -output analogue -to -digital con-verter can be turned into an RS232 -typeserial bit stream. One channel of an ana-logue multiplexer is used to provide twoinputs to the three -digit a -to -d converter.The circuit is suitable for battery operation.

Data is transmitted at 9600 baud, eightbytes every 50ms. One counter/divider scalesoutput of a stable timebase and the othercontrols three analogue multiplexers. One ofthese multiplexers selects from eight inputsto encode serialized bytes representing oneb.c.d. digit.

1 1 0/1 0/1

L input -multiplexing indicator

switch -state indicator

23 22 21 2°

A second counter/divider controls theserialization and digit -select multiplexers toproduce a pattern of eight serial words.

100 1 10 1 100 1 10 1

input 0 input 1

Serialization and digit -select multiplexersinclude pull-up resistors at their outputswhich function as pull-up resistors for the3162 outputs. This feature, made possible bythe analogue nature of the 4051 multiplex-ers, eliminates the need for individual multi-plexers at each 3162 output.

Output from the digit -select multiplexerdrives the timebase prescaler CLEAR input sothat the counter pauses until the desireddigit appears at the 3162 b.c.d. outputs.

The converter performs a dual -slopeanalogue -to -digital conversion in approx-imately 5ms and then outputs the hun-dreds, ones and tens digits consecutively.Each digit -select line is strobed for about5ms. Each digit is available for much longerthan one byte time so the interval is filledwith stop bits.

Only three digits need to be sent todigitize each input but the binary counterdigit -select output has four states. Thefourth digit -select multiplexer input selectsthe ones digit which is transmitted after thetens digit to fill this extra byte time.

Alternatively an And gate feeding Ao,1digit -multiplex inputs could drive theserialization multiplexer inhibit input toprevent transmission of the extra serialcharacter. Input Y3 to the digit -select multi-plexer could then be grounded instead ofbeing connected to pin 3 of the 3162. Thespare section of the 4053 multiplexer couldform this And gate.

The sixth bit of the transmitted word canbe used to represent the position of a switch.Samuel EisenpressSanta CruzCalifornia









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Complex filter using two i.csWhen feeding audio output directly into alow -power f.m. transmitter., severe intermo-dulation occurred due to h.f. out -of -bandproducts. This was particularly noticeableduring tape playback since residual biasnoise caused audible beat notes.

My requirement was for steep roll -offfiltering above 15kHz with a deep notch at19kHz to eliminate stereo -tuner multiplextone. This multiplex -tone and 3 -pole low-pass filter uses only two i.cs and mainlypreferred values. Its response is flat within0.5dB to 15kHz, - 24dB at 19kHz and -



20dB at 30kHz falling at 18dB/octave.A variation elminates the multiplex filter

and gives a four -pole low-pass response butattempts to combine four -pole responsewith 19kHz notch filtering foundered due tocomponent interaction. No doubt computermodelling could overcome this but out herein the middle of the Pacific Ocean we have torely on empirical solutions.Tim MasonRadio VanuatuPort VillaVanuatu

Input stage for 4 polelow-pass alternativeUses component valuesshown in brackets above


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Maxwell's e.m. theoryrevisited

If Maxwell's theory is about to be displaced according tothe many words in this journal recently, we might take a nostalgic

look at it once again.

66 ack to basics," we said, "beforeexpecting a profound paradigmshift. You ought to know a little

about the accepted norm." If Maxwell'stheory is about to be displaced (no pun!)according to the many words in this journalrecently, we might take a nostalgic look at itonce again.

"You don't mean, er, those - curls andthings...?" Not directly, but the curls - andthe grads, divs, dels - do seem to remainunpopular with students, probably thereason is bad teaching again...

Yet the developed theory of electromag-netism still holds sway. If there are somephenomena such a theory does not explain,then any new model must explain all that hasgone before - plus the new aspects. At leastthat is the way Thomas Kuhn outlined thesituation..

But Maxwell remains a good model, dis-placement current and all. In saying this, Ihave mentioned a vital point. It is only amodel, a kind of template held up againstnature, as it were. If the picture fits, so welland good, we can predict some occurancesand design a few things and earn somemoney.

Is it true? That is not a relevant question.We don't really care if it is absolutely true, wecan never know that anyway. The point is,does it work? If yes, we go ahead and makeour name, or even earn the money... Scienceand technology is pragmatic, whether prag-matism (in William James's sense2) is out offashion or not.

For example, electrons - are they reallythere? Is displacement current real? A num-ber of people have become hot under thecollar recently (and not so recently), aboutthe 'truth' of these ideas. But they havemissed the point. Nothing is ever withcertainty proved in science and thereforeneither is the engineering based on it. It canonly be refuted, when it fails to produce thegoods. This time, Karl Popper' had a fewwords to say on the subject, albeit my limitedcomments are a only a brief scratch on thesurface.


When James Clerk Maxwell was at Edin-burgh University, he came into contact withthe philosopher William Hamilton. In the


cut and thrust of ideas, the relativity ofhuman knowledge held sway, becauseHamilton taught that we only know rela-tions between things - not much aboutthings in themselves. This links back to aKantian view. All this affected the youngMaxwell deeply.

At the same time, Maxwell came upagainst the strict teaching and acute ex-perimental methods of the physicist JamesForbes, which also impressed him. It leftMaxwell always aware that his theoreticalconstructs must be refinable in the fires ofexperimental verification - a view rare intheoretical physicists.


A little later, Maxwell deeply appreciated thework of Michael Faraday and one of his firstimportant papers4 on Electromagnetismwas his "On Faraday's Lines of Force" (1856).The 'mechanical' properties of the imaginarylines included the tension in length (whichexplained attraction) and their repulsionsideways (explaining repulsion itself). Max-well modelled these properties mathemati-cally.

This first paper was followed in 1861 bythe paper "On Physical Lines of Force',because in the meantime William Thomson,later Lord Kelvin, had been in lively corres-pondence with Maxwell, and between thepair of them they had noticed all the analo-gies between: stream lines in fluid flow, linesof heat flow, electric current flow lines, linesof force in electric fields and lines of force inmagnetic fields.

These analogy relationships give partialexplanations. They are models, but crossfertilise thinking about different branches ofphysical science. Yet they warn us not tothink electricity is really a fluid water, orreally like a state of heat flow agitation...

Further discussion, this time with Stokes,had Maxwell contemplating Stokes' workshowing that heat flow in a non -uniformcrystal had a direction A not always parallelto the direction of maximum temperaturegradients 0.


where T is a tensor, describing the aniso-tropic crystal. Maxwell immediately appliedthe analogy to magnetism and distinguished

the two vectors which he called the "flow" Band the "force" H and realised that in ananisotropic magnetic medium (like some ofour modern ferrites), the lines of force wouldnot always be parallel to the lines of flux. Thedirect analogy in the electric case was flowlines of current density J, with the force Esetting them up.

The trouble is that generations of studentshave been perplexed by these two 'different'vectors B and H describing the same thing -magnetic field. You might have found thisbecause of bad teaching again and a glance atthese original papers often helps.


The analogies led Maxwell to discourse ontwo classes of vector functions existing ingeneral, fluxes and forces. A flux B is subjectto a continuity equation and is integratedover a surface. The picture is 'streamingacross'. A force P is a vector which is usuallyderived - but not always - from a singlevalued scalar function, the potential and isintegrated along a line. It gives the concept'force along'. The vectors B and J are fluxes,H and E are forces.

In Maxwell's earlier discussions and grow-ing mental pictures, he stuck to three-dimensional Cartesians (the x,y, z axes). Butby 1870 after much correspondence withPeter Guthrie Tait and William Thomson,Maxwell' himself advanced the ideas ofconvergence (negative divergence), the curland slope (later called the gradient). Theextract from his paper is interesting:

. . Va has, in general, also a vector portion,and I propose, but with great diffidence, to callthis vector the Curl or Version of the originalvector function.

It represents the direction and magnitude ofthe rotation of the subject matter carried bythe vector a. I have sought for a word whichshall neither, like Rotation, Whirl, or Twirl,connote motion, nor, like Twist, indicate ahelical or screw structure which is not of thenature of a vector at all."

\ 1 /t \ 1 -. \

....... ........0 / I

Convergence Curl Convergenceand curl


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Maxwell found Tait's enthusiasm for 'qua-ternions' invented by William Hamilton (notthe philosopher, but another Hamilton, themathematician), had given him the germ ofvector analysis - especially via the use ofHamilton's operator V. There was muchhumour in Maxwell's correspondence aboutV and his play on words regarding thepossible names for it: Nabla. or even Atledhad been suggested'.

Maxwell did not fully adopt the compli-cated quarternion ideas, but used the form,

d d

=jai+jzi+ k-dx

and realised the vector properties of it inconnection with the 'div' and 'curl' opera-tions. It remained to Willard Gibbs in apamphlet and Oliver Heaviside to oust'quaternions' but to bring in the full modernvector analysis notation. You will still find itmost entertaining to read Heaviside's pithycomments about Clarendon type faces andother notations. Maxwell and certainlyHeaviside would immediately recognise ourmodern presentation of the equations.

Advancing an argument started by Thom-son, Maxwell showed that any flux vector hadtwo parts. It had a component from the curlof a force vector plus another part which wasthe gradient of a scalar function. Formagnetism he wrote,

B=curlA + gradlif

and went on to say that in the absence ofmagnetic poles (or isolated magneticcharge) there are no sources and thereforegradll =O.

Therefore he had obtained a complete setof equations between B, H, J and E. At thisstage, still using Cartesian mathematicalarguments, Maxwell showed Faraday's elec-tromagnetic induction is described in ourmodern notation by,

curl E= - aB

and from this, by using B = curl A showed

aA aAcurIE=curl(-at) or E= - -at

Maxwell called this new function A the"electrotonic state" in recognition of Fara-day's speculations about a hypothetical stateof stress that must surround electrically ormagnetically 'charged' bodies.


You will find Maxwell's struggles with howthe fields extend around the sources con-tained in the second "lines of force" papers.He tries analogy again with a kind of mecha-nical vortex model, see Fig.1. He extendedthe model from matter to space, postulatingan ether to contain the vortices. Considerthe array of vortices embedded in an incom-pressible fluid. When they rotate, centrifugalforces cause them to contract longitudinallyand they exert radial pressure. This is exactlyFaraday's proposal about the properties oflines of force.

But the concept drove Maxwell to see thatelectricity was not confined to a fluid in the

Maxwell's Figure 2 in his paper, "On Physic-al Lines of Force". The electric current wasrepresented by the 'ball bearings' runnirgfrom A to B and the resulting vortex moticnwas given to the imaginary 'cells' in thesurrounding space as shown. The line p toq shows what would happen if anotherconductor was placed along there, thusexplaining induction. One or two of therotation direction arrows are incorrect.

The flow lines of a current form closedpaths according to Maxwell. This meansthey must pass through the dielectric of acapacitor. including a vacuum. All thecurrent there must be in the form ofDisplacement or Electric Flux variations asno actual electrons are emitted throughthe region.

conductor on this view of things, but wasdisseminated in space - and the energy was'stored' in the space containing the fields...The function A, which we now call the vectorpotential, acted as a kind of momentumterm in the field. The equation E = aA/atwas equivalent to Newton's equation be-tween force and rate of change ofmomentum.

Now Maxwell hit upon the idea that themedium containing the vortices was elastic- hence the energy storage in the mediumwas by an elastic distortion. Two remarkableconsequences quickly follow. Since thespace surrounding a conductor is capable ofan elastic displacement - a varying fielddisplaces an equivalent current. This is thefirst glimmering of the "displacement cur-rent" postulate. Secondly, any elasticmedium with density p and a shear modulusm can transmit transverse waves with avelocity,

v= A rV P

Maxwell inserted magnetic and electric

quantities (based as we now say on permit-tivity and permeability) and found the wavevelocity would almost equal the thenaccepted value of the velocity of light. Withsome excitement he wrote in the "Lines ofForce..." paper

"The velocity of light in air, as determined byM. Fizeau*, is 70,843 leagues per second (25leagues to a degree) which gives

V=314,858,000,000 millimetres= 195,647 miles per second (137)

The velocity of transverse undulations in ourhypothetical medium, calculated from theelectro-magnetic experiments of MM. Koh-lrausch and Weber. agrees so exactly with thevelocity of light calculated from the opticalexperiments of M. Fizeau, that we can scarcelyavoid the inference that light consists in thetransverse undulations of the same mediumwhich is the cause of electric and magneticphenomena".

By 1865 Maxwell had written his paper "ADynamic Theory Of The EjectromagneticField"9. In it, he spelt out the full develop-ment of how the electromagnetic waveswould propagate. Note the word "field"appears for the first time in the title. He haddropped the "vortices" intermediate analogystage and relied on a few facts including thereally original concept of the 'displacementcurrent'. He effectively noted that themagnetic current is always a 'displacementcurrent' aBiat as there is nomagnetic chargein the Universe. Therefore why not some ofthe electric current at least in the formmat? The total current then, is alwaysclosed and is a set of flow lines


where J' is the total current, J the conduc-tion current and aD/at is the displacementcurrent, D now being the electric flux ordisplacement vector. A changing currentmight set up a flow pattern in a capacitor likethat in Fig.2.


Maxwell saw the significance of his con-struct. He wrote to his cousin, Charles Cay,"I have also a paper afloat, containing anelectromagnetic theory of light, which till I

am convinced to the contrary, I hold to begreat guns."

Again, the philosopher Hamilton's influ-ence on Maxwell in his youth can be seen.The build up via analogies, his developmentof the mechanical model - and then drop-ping it, and finally the analysis of the directrelations between the two classes of phe-nomena (magnetism and electricity) as aunifying structure - are all based on Hamil-ton's doctrine of the relativity of knowledge.Einstein said of Maxwell that he saw thefuture role of field theory in physics, com-plete with its describing differential equa-tions and seeing that was his stroke ofgenius.

The revolutionary idea is not really thedisplacement current proper, (in spite of theheat under many collars!), but the whole'dissemination' idea into the medium. Max-well's formal energy densities in the mediumwhich also link with some of Thomson'swork, encapsulate this view:


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magnetic energy density =m

and electric energy density = D.E

Maxwell writing at the end of his "Dyna-mics..." paper, even calculated the peakvalue of the electric field in sunlight, both inthe solar constant at the Earth's surface andat the sun.

"The energy passing through a unit of area is


so that P=

where V is the velocity of light, and W is theenergy communicated to unit of area by thelight in a second.

According to Pouillet's data, as calculatedby Professor W. Thomson, the mechanicalvalue of direct sunlight at the Earth is 83.4foot-pounds per second per square foot. Thisgives the maximum value of P in directsunlight at the Earth's distance from the Sun,P=60,000,000, or about 600 Daniell's cells permetre. At the Sun's surface the value of Pwould be about 13,000 Daniell's cells permetre."

The model Maxwell gave explained andpredicted optical and electrical phenomenawith great vigour and precision. Whichevervectors you take, strictly transverse waves inspace appear because of the vector productnature of curl. The equations are the 'tele-graphers equations' of space, and look likethe transmission line equations Heavisidederived for waves on wires later:

apcurl H = + -at

aBcurl E = -t

div B = 0

div D = p.

with D = EE

B = 1.LH

J= crE

The wholly transverse solutions eliminatedthe longitudinal wave requirements that hadembarrassed earlier theories of light.

Heinrich Hertz's electrical generation anddetection of long maxwellian waves, with allthe predicted properties was a supremevindication. The vast proliferation of en-gineering uses of these waves up to thepresent time is a further supreme example.


But just as important, Maxwell predictedthat the waves would exert a radiationpressure - thus disposing of the idea thatany luminiferous pressure would be a crucialargument for a corpuscular theory of light.Lebedev proved the radiation pressure post-ulate experimentally in 1900. It explains therepulsion of parts of the tails of comets. Suchradiation pressure is vital for Black Bodyradiation theory. It may be used to deriveclassically the time dilation formula of spe-cial relativity and explains how stars hold upinternally, together with their allowed massrange...

Maxwell's famous Treatise"' sets out theon -going work in book form, but adds little

more to his papers and memoirs. In the late1870s he was about to write a deeper inves-tigation into all these researches, but sto-mach cancer heralded his early death aged48 in November 1879 - at the prime of hispowers. As usual, we always speculate onwhat he might have achieved had he lived.

References1. T.S.Kuhn, The Structure of Scientific Revolu-tions Univ. Chicago Press, 1970.2. W.James, Pragmatism and Four Essays fromthe Meaning of Truth, Meridian Books, 1963.3. K.R. Popper. Conjectures and RefutationsR.K.P. 1972.4. J. Clerk Maxwell, On Faraday's Lines of Force,Scientific Papers, 1855, 1856, reprinted by Dover,New York, 1952.5. J.Clerk Maxwell, On Physical Lines of ForceScientific Papers, 1861, 1862.

6. J.Clerk Maxwell, On the Mathematical Classi-fication of Physical Quantities, Scientific Papers.7. Maxwell had much to say with Tait, Thomson,and many others via the 'halfpenny post' after thePost Office introduced it in 1869. Tait was knownas T' and Thomson as T'. These two authors wrotea "Treatise on Natural Philosophy" which wasreviewed by Maxwell - who henceforth referred toit as "T and r". Tait couldn't stand Tyndall,another scientist in the milieu, and referred tohim as r ('where r is a quantity of the secondorder...). Tait had written a book on Thermodyna-mics in which he had given an equation dp/dt=JCM. Maxwell then signed his cards:"...yourssincerely, dp/dt."8. 0. Heaviside, Electromagnetic Theory vol.l.chap3, The Elements of Vectorial Analysis andAlgebra, The Electrician 1893, Dover reprint.9. J.Clerk Maxwell, A Dynamical Theory of theElectromagnetic Field, Scientific papers.10. J.Clerk Maxwell, Treatise on Electricity andMagnetism, Oxford, 1873, 2nd. ed. 1881, 3rd. ed.1891.

Dividers faster than 3GHzBipolar devices offer better phase noise and speed powerperformance than gallium arsenide equivalents

Advances in semiconductor proces-sing and photolithography at Plesseyhave produced the first prescaler i.csfor frequencies above 3GHz. Theyincorporate silicon biploar transis-tors with 1.5p.m emitters and 7GHzf, at 0.5mW dissipation. Couplingthese transistors with 5µm -pitchmetal combines the high speed withhigh packing density.

Work is currently being done toincrease speed of the new dividers to6GHz, which will make them usefulfor applications like directly synthe-sizing local oscillators in C -band

satellite receiver front ends.Initially, the SP8800 prescaler

series consists of divide -by -two, four,eight and ten i.cs in surface -mountand dil packages. Sensitivity andoverload performances are good, asFig. 1 shows, and power dissipation/radiation are low. Being bipolar, thedevices inherently offer better phase -noise and speed/power performancethan GaAs equivalents.

Applications include counter pre -scaling and frequency synthesis. Fi-gure 2 represents a 3.5GHz frequen-cy synthesis loop with one of the newprescalers dividing by four and anSP8704 dividing by 128 or 129. Withthe world's first military -speci-fication 20mA 1.5GHz synthesizer,Fig. 3, it will be possible to produce atwo -chip military -grade frequencysynthesis loop.

The SP8850 is currently underdevelopment: samples should be

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2 3


Output 0 S to 3.5 6Hz Fig.2

Dual modulushigh speed

4 3 56Hz divider 5 nthesizer

Output 0.5 to 3 3 GHzH,gh speed divider

-4 33GHz /synthesizer


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HfflouBliff ELS



IBM PC (and compatibles), RM NIMBUS, BBC MODEL B,B+ and MASTER, AMSTRAD CPC and SPECTRUM 48K"ANALYSER" I and II compute the A.C. FREQUENCY RESPONSE oflinear (analogue) circuits. GAIN and PHASE INPUT IMPEDANCE,OUTPUT IMPEDANCE and GROUP RELAY (except Spectrum version) arecalculated over any frequency range required. The programs are in useregularly for frequencies between 0.1Hz to 1.2GHz. The effects onperformance of MODIFICATIONS to both circuit and component valuescan be speedily evaluated.

Circuits containing any combination of RESISTORS. CAPACITORS,INDUCTORS. TRANSFORMERS. BIPOLAR and FIELD EFFECTTRANSISTORS and OPERATIONAL AMPLIFIERS can be simulated - upto 60 nodes and 180 components (IBM version).

RI no




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Tabular output on Analyser I. Full graphical output, increased circuit size andactive component library facilities on Analyser II.

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ANALYSER can greatly reduce or even eliminate the need to breadboard newdesigns.




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....0 ............

TT* - ................. - ---_____:-..... .....____ ..........


A powerful control computer based on the new Hitachi6303Y and high level language Forth. 100mm x 72mm.30K bytes RAM, 16K dictionary RAM 'PROM, 256 bytesEEPROM, 16K Forth. You can attach 64 key keyboard,LCD and PC bus peripherals. Built in are interrupts,multitasking, time of day clock, watchdog timer, fullscreen editor and symbolic assembler. 32 parallel and twoserial ports. Single power supply and low power 3mAoperational mode.

1 off £194.95 including manual and non-volatile RAM.


Triangle Digital Services Ltd100a Wood Street, London E17 3HXTelephone 01-520-0442 Telex 262284 (quote M07751

Toroidal &TransformersAs manufacturers we are able to offer arange of quality toroidal and laminatedtransformers at highly competitive prices

Toroidal Mail Order Price Listprices inclusive of VAT & Postage15va 7.95, 30va 9.18, 50va 10.16. 80va 11.36. 120va 12.07, 160va 14.20, 225va15.21 300va 17.04, SOOva 22.10, 625va 24.66. 750va 28.75, 1000va 44.82.Also available 1k2. 1k5. 2k. 2k5. 3k. Prices on request.

Available from stock the following voltages: 6-0-6.9-0-9. 12-0-12. 15-0-15. 18-0-18,22-0-22. 25-0-25 30-0-30. 35-0-35, 40-0-40. 45-0-45. 50-0-50. 110, 220. 240.Primary 240 volt.

Quantity prices and delivery on requestAir Link TransformersUnit 6. The Maltings, Station Road,

Sawbridgeworth, Herts. Tel: 0279 724425ENTER 26 ON REPLY CARD







R. Henson Ltd.21 Lodge Lane, N. Finchley, London, N12 8JG.

5 mins. from Tally Ho Corner

Telephone: 01-445 2713/0749




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APPLICATIONS SUMMARYDIGITAL SIGNALPROCESSINGSignal processing using analogue methods,where time and/or amplitude are con-tinuous quantities, has several disadvan-tages compared to digital methods wheretime and amplitude are discrete quantities.State-of-the-art analogue -processors areapproaching the limits of integration forsilicon and their parameters are difficult torepeat reliably in mass production: timeand temperature instabilities are also aproblem.

New digital -signal processorarchitectures increase processing speed. Se-quential processing (von Neumann) using asingle bus architecture, where instructionand data signals share a common path, hasbeen replaced by parallel processing (Har-vard). In Harvard architecture, instructionand data paths are separated. This enablesspeeds to be increased by pipeline processingin which several tasks can be accomplishedin a single instruction cycle.

Three stage pipelining (top diagram) isused with NEC's HPI)77230 to fetch aninstruction, execute an instruction and storeresults in parallel during a single 150nscycle. The 77230 advanced signal processorcan he operated in either master or slavemode (bottom).

NEC applications handbook 'Increase






Floating-point multiplierFMPY 32bit data registersFMPY multiplication result

Arithmetic and logical unitExponent a.l.u.ALU/EAU date i/p registersShift and count registerBarrel shift registerShift value registerWorking registerProcessor status wordsWR transfer control

Data memories

RP Date rom pointerBASEO.1 Base pointersINDEXO.1 Index registersADD Adders

Instruction rom

PC Program counterSP Stack pointerIR Instruction registerDECODE Instruction decoder

Parallel interface


Date portAddress portData registerSlave data registerAddress registerRead/write control

Serial tio interface




Serial output registerOutput shift registerSerial o/p control reg.Serial i/p data registerInput shift registerSerial input control

Interrupt controllerTemporary registerLoop counterStatus register

number crunching capabilities: digital sig-nal processors' discusses the use of d.s.processors and applications includingnumerical control, speech processing, in-strumentation and telecommunications.


VO 0-15CS




DO -D31 w v

AO -All





512 W 32ba




512 W 32ba







2 KW x 32bet






















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80uH each oncommon core





>220k 2k2




100p I10N S1k3 I510p 1100n I10N

MC 34129

Ps ucontroller









(' 44 T1°°P1N5819

MOC 5007


Sync in




S1 Closed = on hookOpen-= off hook









1k 1620 1



MC 34119

1t 75k 100k 10E -0-n-

5Vino ( Ii

01 1N4148 02 CO 1 4 1"\/\+-410

6 3 100kVcc FC1


TTMAll 100nm,..


C3 E. " I

R1OSC L--i


10 500kHz

FIT) 11S2

I-4-4 Vss 6 eDTMF OH 12

ISO 0,'L 17


0k 22k <22k5













1° vLS














100kN 3904

10k 10k I, 10k


2 N 3904


Sync topower supply



MC 145 406


10 7

11 6

13 4

12 5

14 3

18 2

8 r-E-5v






+51/ MC145428


























DL 3






MC 145 4 26

+11502 vdd8 16


401 PD6 15

S:1 X17








o ,(;)o -oo

00 o

+5 VAllIA s-0-







L _ JS3 to S7


20 p

10y /A .-- I-20


L02 s /VV\.,-.4 1

L --ir QLOI

21----t-'VV\i-'L 13 , 'WNW.






.i.- mr

11Vss Vref

L100n Line transformer



To psuiVin






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Digital voice/datatelephone setDesign of a digital voice/data telephone setis discussed in Motorola note AN968. Thistelephone set provides standard analoguefunctions while simultaneously transmit-ting 9600 baud asynchronous data from acomputer or terminal.

The voice/data i.cs used are from theMC145422/26 universal digital -loop trans-ceiver family. They provide 80kbit/s full -duplex synchronous communication over2km on one twisted pair. A pulse/tonedialler and c-mos RS232 i.c. for com-munication with a computer or terminalare included in the design and an efficientswitching p.s.u. provides an isolated supplyfrom the twisted pair's 48V.

Traditional tone signalling on the voicechannel is used. Looked at from the p.b.x..the voice/data multiplexer appears as anordinary telephone. The handset cradleswitch is replaced by a relay. S1, that openswhen the telephone is lifted.

Voice and data signals are converted todigital form compatible with the u.d.l.t. bythe 14403 codec/filter and 145428 data -setinterface respectively.

Ringing signal from the p.b.x. is de-tected, sampled and sent to the digitaltelephone where it feeds a loudspeaker

Connectionto externalterminal orcomputer

MC 145406RS -232 driver


M 1',




MC145428data -setinter face



through an amplifier. Analogue voice sig-nals are digitized and reconstructed by thecodec/filter duplexer which is linked to thep.b.x. wires via the u.d.l.t.

Asynchronous data to and from thecomput or data switch passes through thedata -set interface. Outgoing RS232 data issynchronized and sent to the u.d.t.l. full -duplex data channel at 8k bit/s. Conversionof incoming synchronous data to asynchro-




MC 1454'pulse/to,c



7 619s0

ML 3,.129

switchingpower supply( isolated)

Line -interface

( transformerand=lion)

"141" ..^V;


nous form is also performed by the data -setinterface.

Direct current is applied to the twistedpair at the multiplexer and transputed overthe wires, so no extra supply lines areneeded.

Full constructional details are includedin the seven -page note. A further note,AN949, describes the voice/data multi-plexer.

Optimization of led operating conditions isdiscussed in Three -Five Semiconductor'snote No.1 . With low -voltage d.c. supplies,connecting a led is simply a matter ofcalculating an appropriate voltage -droppingresistor. Where the voltage drop is large orpower consumption is important, low -powerleds can be particularly beneficial.

With high voltage a.c. supply simpleresistive voltage -dropping elements arewasteful, can be physically large, and do nottake into account led reverse voltage. Thereare more efficient ways of driving leds froma high voltage a.c. source as this tableshows.

Also included in the note are equations forcalculating the voltage -drop elements andfurther information on each of the sixmethods.

+V Vmains


Supply 2.2V. V 0 6V 20mA standard led 10mA high efficiency 2mA low current Unit Light output

1 12Vd.c


Power dissipated4900.196

9800 098


11 Constant

2 240Va.c


Power dissipated59304.74

118602 37

593000.47w Pulsed 50Hz

3 240Va.c.


Power dissipated59459.51

118904 76


Pulsed 50Hz

4 240Va.c


Power dissipated118304 73

236602 37

118300047w Pulsed 100Hr

5 240Va.c.


Power dissipated0.533Negligible



F Pulsed 50Hz

6 240Vac


Power dissipated0.269Negligible


0 026 F

NegligiblewPulsed 100Hz

Vmoins Vmoins Vmoins


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HLF 4001B

( I. in parallel)




BA 221

10k 1M1



4 2V


68k 36k5

BC 558

BC548 BC 548

VD=4 5V

1 M 90k9



0 to 1V 1kfor digital

19k6 readouts



Adjust C4 after half an houruntil meter reads 44%

Humidity sensor

Temp@ioiure C) 15 20 25

J "Potassium carbonate(K2CO3)

Battery poweredhygrometer

low-cost hygrometer running from a1000. 4.5V supply is one of five applicationsin the first VT & S Bulletin from Mullard.Electronic hygrometers are lightweight andeasy to maintain, operate and calibrate.Having electrical output, they are easilyinterfaced to other electronic equipment.

Capacitance of the dielectric -

foil sensor varies with relativehumidity. At 43% relativehumidity, the sensor is 122pFwithin 15% and its range is 10 to90% r.h. Frequency of one of thetwo RC oscillators shown is fixed:in the other oscillator. C of theRC network is the sensor so itsfrequency varies with relativehumidity.

Frequency difference between the twooscillators is translated into a pulsed voltagewith an average value proportional to themark/space ratio. This voltage appears at thebuffer i.c. output. Because the sensor char-acteristic is non-linear the average valuevaries non -linearly with humidity. A diodeand passive components following the bufferlinearize drive for the meter. pen recorder orled display.

For calibration. the sensor is replaced by a2% 118pF capacitor and the fixed oscillatorfrequency adjusted for minimum meter

Supply -voltage supervisorWhen a simple RC network controls thereset line of a microprocessor certain typesof power failure can result in incorrectresetting.

At power up the TL7705 supply -voltagesupervisor delays rising of the reset line untilsupply voltage is fully on. as does an RCnetwork. Unlike the RC circuit though, the7705 pulls the reset line low when supplyvoltage falls below 3.6V. When supply vol-tage rises above 3.6V, the reset line goes highafter a delay proportional to CT. Output isundefined when supply voltage falls below9v.

This circuit is from the Texas InstrumentsTL7705 applications sample available todesigners. A small p.c.b. and three passivecomponents are included in the kit.

Reset generator







reading. This capacitor is then replaced by a

2% 159pF capacitor and the meter potentio-meter is adjusted for maximum meter read-ing. With the sensor in place, the variablecapacitor in the fixed oscillator is againadjusted until a known humidity is correctlydisplayed. Potassium carbonate in a sealedjar can be used for this. Operating frequencylimits of the sensor are lkHz and 1MHz.

Other notes in the VT & S Bulletin(varistors. thermistors and sensors) coverback-up lighting for fluorescent lamps atswitch on, colour tv e.h.t. supply protection,shaver -socket protection and using zinc -oxide varistors.


Three -FivePO Box 131, Swindon.Wiltshire SN2 6XDTel. 0793 618835

NEC ElectronicsCygnus House.Sunrise Park Way,Milton Keynes MK14 6NPTel. 0908 691133

MullardMullard HouseTorrington Place

London WC1E 7HD01 580 6633

MotorolaITT Multicomponents346 Edinburgh Avenue,Slough.Berkshire SL1 4TUTel. 0753 824131

Texas InstrumentsOnline DistributionMelbourne HouseKingswayBedford MK42 9AZ0234 217981

FICreset networ7


10ke_s_xR SET'

'00n I M.

I T10P



GNI],L _


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Intermural tv signalsIt is sometimes forgotten that a simple half -wave dipole

correctly positioned can give a signal greater than the usualminiature indoor Yagi-t'da or log periodic antenna.

Television signals show regular stand-ing wave patterns of maxima insidebrick buildings. To investigate tyhe

usefulness of this effect I made measure-ments of the geometry and magnitude of thesignal pattern set up by the 0.51CHz radia-tion from the Sandy, Beds transmitter in abrick room at grid reference 761431. Themeasuring system comprised a half -wavedipole with a sleeve balun feeding a TESMC661C signal -strength meter.

Measured along a line parallel with they-axis the distance between successive signalstrength maxima was 42.7cm and, normalis-ing the peak signal amplitude to unity, theamplitude at the minima was 0.32. Resultsparallel with the z-axis were 24.0cm and0.75. These are sketched below.

At the position of minimum signal thedirection of polarization was that of theincident signal, approximately N -S. Awayfrom the minima it varied between direc-tions parallel to the y-axis and to the z-axis.


The observed signal patterns were tested forcompatibility with either a Fresnel or aFraunhofer diffraction pattern orginating inapertures formed by the irradiated walls.They did not fit either form but a system ofinterference between direct radiation in theroom and wall -reflected radiation was foundto agree with experiment.

Consider next, direct radiation alongd intersecting the once -reflected radiation rat the point la,b), as depicted next column.The geometrical path difference between dand r is 2cos O ID -b). Allowing for a IT phasechange on reflection the optical path differ -

Z4 32


42 7tm

0 24 Otm

ence is 2cos 0 ID - b) + X/2 where X is thewavelength of the radiation. For the point(a,b) to be a position of maximum signal

2cos0 ID - b) + X/2 = nA

where n is an integer. The separation invalues of b for successive maxima is then

(X/2) seal.

This is then the peak separation along thez-axis.


The reflected wave fails if the y -value of thepoint of incidence of r is negative, i.e. where

a<4 ID - ['flan°.

In addition, the optical path difference mustequal or exceed A for a maximum to bepossible and so

b. -5D- (X/41sec0.

Note that this maximum value for b will bevery sensitive to A if 0 approaches ir/2.

A similar analysis for radiation reflectedfrom the wall at y = W gives the peakseparation along the y-axis as

(A/2). tan 0. sec 0

This maxima pattern disappears if

a<W- B tan 0


aL5W-(X/4)tan 0. sec 0.

Equating measured and analytical values forpeak separation along the z-axis gives

42.7=(A/21 tan 0 sec 0

and for the y-axis

24= (X/2) sec 0


0 = 60.8° and A = 23.4cm.

The value of 0 agrees reasonably with thecompass value of radiation direction. Thefree -space wavelength A = 58.8cm and soXIA =2.5.

Moreno discusses the effect on wavelengthof the presence of dielectric material in an

enclosure showing, for microwaves, a valueof 1.5 for XIX with material having adielectric constant of 2.45. I suggest thatbrickwork shows a dielectric constant ofabout 7 for the 0.51CHz radiation underinvestigation, making the value of 2.5 forXIX reasonable.

lithe reflection coefficient of the wall is Rthen the intensity maximum is proportionalto (1-R) + R(1- R) and the minimum to(1-R) - R(1 -R). The ratio of maximum tominimum amplitude will be (1+ R)/(1- R).Thus for y variations:

max/min = 3.25 .*. R = 0.28

reflection angle = 90° - 60.8° = 29.2°.

For z variation:

max/min = 1.33 .*. R = 0.06

reflection angle = 60.8°

For radiation polarized normally to theplane of incidence the reflectivity should fallto zero when the incident and refractedangle add to 90°. If the incident angle is i andthe refractive index q then

i + sin '(sin = 90°

for zero reflectivity. As R falls from 0.28 withan incident angle of 29.2° to 0.06 at 60.8°,crude extrapolation puts R = 0 at an incidentangle of 69°, hence

69° + sin 2 Isin69/N ) 90°

making 11 - 2.6 and hence the dielectricconstant - 6.8.

This analysis assumes throughout thatthe incident wave is parallel to the ground,or approximately so.


At a maximum the internal signal intensityshould compare with the external value as((I -R) + 1211- R)):I. Taking the reflectivityR as 28% this ratio is 0.92:1 giving aninternal signal amplitude of 96% of theexternal magnitude. The introduction of alarge capture -area antenna into the enclo-sure must be avoided or the signal patternwill be disturbed and constructive interfer-ence lost.

If an analagous pattern were obtainedfrom the proposed satellite broadcasts itcould be exploited. possibly by a printedarray of linked dipoles with their size ad-justed to accord with the diminished inter-nal wavelength'. Such a system would avoidthe cost and aesthetic objections that roof -mounted dish antennas may generate.

I. Microwave Transmission Data. T.Moreno. Dover Pub-

lications. 1958.


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[CIRCUIT IDEAS03 Q2 Q1 Q0 i/p o/p Q as a

functionof Q0













RY generator forRTTY




When designing hardware and software forRTTY reception it is useful to have a constantsource of RTTY data.

Three outputs from a clocked 4 -bit coun-ter feed A, B and C inputs of a multiplexer toselect one of eight inputs.

RTTY characters consists of at least sevenand a half units; a start bit, five data bits andone and a half stop bits. Using two stop bits,as with this circuit, does not cause problems.

Characters R and Y are usually used as atest message since they are complementary.For characters RY, the bit pattern is10010101 10101011. The counter's least -

significant bit provides the multiplexer datainputs.

As Q is a t.t.l. signal it can be used to drivethe input of the computer directly. To allow

L. 16


ruR1 112


15 DO,







2 9

6 10



Baud C1 R1

















Shift Morkfreq.













150n 11c5



B 113










1 I4





560 1k

T 330n







R5 <1k C4 100n

testing of the terminal unit, two spare Nandgates provide mark and space frequency;Values of R2 and C2 determine frequengshift. Each oscillator is enabled by Q and Q

Phase -check pulse generatorWitches -hat pulses like those often used toindicate phase on circuit diagrams are im-mediately obvious on an oscilloscope screen,unlike narrow rectangular pulses where theedges tend to disappear.

Low impendance output is provided by aunity -gain buffer: pulses produced are atlkHz with a peak level of 1V.D.R.C. SelfLondon.


--VV\ -0--10k



Witches hot

22k Op -amps ore TL 074 or TL07 2

Diodes are general purpose silicon

outputs from the multiplexer.Mixing of mark and space frequencies is

done with a simple transistor Nand gate builtaround D1, D2 and Q1. Output is low-passfiltered by R6 and C. Reverse sense RTTY isobtained by swapping over Q and 0-multi-plexer outputs.P. HarrisonLichfieldStaffordshire






to op-omps _L9V


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Universal voltage -

controlled oscillator withlow phase noise

An analysis of noise behaviour for a variety of v.h.f. transistorsshows that a j-fet produces the lowest phase noise.

For use in a v.h.f. synthesizer, a voltage -controlled oscillator was required withlow phase noise. The design was to be

such that only the mounting of a suitable tankinductor would guarantee operation at anycentre frequency in the band between 10 and300MHz. As there is no general agreement onwhich kind of transistor provides the lowestnoise in oscillators, the effect of transistornoise was investigated both theoretically andexperimentally.

In the general v.c.o. circuit of Fig.1, themost suitable frequency determining elementis an LC resonator electronically tuned byvariable -capacitance diodes. The drawback isthat the frequency is a non-linear function ofthe voltage, which results in the conversion ofamplitude into phase noise. The same phe-nomenon occurs in the internal capacitancesof the semiconductor devices in the amplifier.This counteracts the reduction of the phasenoise normally expected when the oscillationamplitude is increased. Therefore there issome optimum oscillation amplitude forminimum phase noise. This explains thenecessity of the amplitude control in Fig. I.

So that the oscillation -sustaining amplifierdoes not affect the resonator Q. its input andoutput resistances should be much higherthan the resonator resistance R.. Hence theamplifier can be modelled as a voltage -controlled current source. which is character-ized by its large -signal forward transconduct-ance Win). The oscillation amplitude is

determined by

1 - SIN/in) Zrdn = 0 ( 1 I

where n is the voltage transformation ratio ofthe resonator. The large -signal transconduct-ance can easily be determined graphicallyfrom the V -I transfer characteristic of theamplifier. This is shown in Fig.2 for anamplifier with a single transistor. For a stableoscillation amplitude, it is necessary that S is adecreasing function of V. This is generallynot the case for a single -transistor amplifier,apparent from Fig.2, at least not if the inputdirect voltage of the transistor is constant orcannot change very fast (within a few periodsof the oscillation). The oscillation amplitude isfinally limited by the supply voltage. This is tobe avoided, however, because the transistorimpedances will, in part of the oscillation


Z res





Bufferamplifier bout

Fig.1. Non -linearity of semiconductor junc-tions results in conversion of amplitude intophase noise which counteracts the reduc-tion of noise due to increase in amplitude -hence the need for optimization. Oscillationamplitude is related to transconductance(see text), obtained graphically from V -Itransfer characteristic, Fig2.

period, be very low and strongly non-linear,resulting in increased phase noise.

This was the main reason to use a differen-tial amplifier. Its large -signal transconduct-ance decreases with increasing input ampli-tude. Fig.3. at least if it is greater than theinput offset voltage. In addition, the input andoutput impedances of a differential amplifierare high, also when its output current satu-rates. Furthermore, the differential amplifierdoes not invert the phase, so that the resona-tor needs in principle no tap or coupling loop.


The basic oscillator circuit is shown in Fig.4with fets. but bipolar transistors could also beused. The noise of this circuit has beenanalysed Iref.1) under the assumption that theparasitic capacitance C, of the source biascircuit has been compensated by the capacitor

VI V2 Val

C (ref.2). The result is the well-known for-mula

FkT f (2)PQM/

where F is the noise figure of the amplifier. fthe frequency of oscillation. P,, the available


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Fig.3. Unlike a single -transistor amplifier a differential amplifier has the virtue thatlarge -signal transconductance is a decreasing function of input voltage.



Fig.4. Basic oscillator uses fets. though bipolar types could be used. which turn out toproduce a lower phase noise by as much as 10dB.

resonator power V2/812, and c is a factordepending on the amount of a.m. to p.m.conversion, which equals 0.5 for low oscilla-tion amplitudes V and 1 for the optimumvalue of V. The noise figure F for thedifferential amplifier is

I + for V < Vm 11 +c for Vo VmIbV

1.)swhere b = 0.5 for bipolar transistors and b =1.5 for junction fets, Vm is defined in Fig.3 andcan be considered as the maximum inputamplitude for which the amplifier workslinearly, and is the phase shift of the amplifer.Base and input resistances of the bipolartransistor have been neglected. The formulaapplies for a resonator transformation ratio of1 and it has been shown that this ratio isoptimum with respect to phase noise.

Formula 3 predicts that the lowest phasenoise can be obtained using junction fets: for adifferential amplifier with junction fets, Vm istypically 1 to 2 volts, whereas for a differentialamplifier with bipolar transistors Vm is only50mV. This accounts for some 10dB differencein phase noise.



Current noise injected into the resonator bythe buffer amplifier is amplified with theoscillator closed loop gain 1/( I -S Zrejn) andshould thus be kept as low as possible. Voltagenoise is of minor importance, since it does not

enter the oscillator. It only produces a noisefloor which could raise the phase noise farfrom the oscillation frequency.

The input noise current density of both abipolar transistor and a junction fet is pro-portional to gn,Ifif1I2 for high frequencies.with gm the low frequency forward transcon-ductance. The best input device for the bufferamplifier is thus a low gm junction fet withhigh transition frequency. The buffer inputcapacitance which loads the resonator isnon-linear and may be lossy at high frequen-cies, and so it should be minimized. A sourcefollower loaded by the high input impedanceof an emitter follower keeps the influence ofthe gate -source capacitance low because thereis no significant r.f. voltage across it. Theemitter follower can provide the output powerto drive e.g. a 50ohm line.

Current noise injected into the resonatorcan be further reduced by taking the bufferinput signal from the sources of the oscillatortransistors.

If the collector of a bipolar transistorproviding the tail current of the differentialamplifier is coupled directly to the sources ofthe oscillator transistors, half of its currentnoise will enter the resonator. This noise canbe an order of magnitude higher than thecurrent noise of the oscillator transistors andwould therefore significantly increase thephase noise. The tail current source shouldtherefore be carefully isolated from the oscil-lator circuit for high frequencies. The isola-tion also eliminates an extra non-linearcapacitance in the oscillator circuit and soreduces a.m. to p.m. conversion.


Low frequency noise, in particular Uf noise.modulates the transconductance and junctioncapacitances of the oscillator transistors andso causes amplitude and phase noise. Theamplitude noise is further converted intophase noise in the voltage -dependent junctioncapacitances.

The use of low frequency feedback de-creases the noise in the collector or draincurrent and so the transconductance fluctua-tions. Further, the gate or gate bias circuitshould have a low impedance at low frequen-cies. In bipolar transistors, the la noise sourceworks in parallel with the base -emitter junc-tion current noise source and therefore theeffect of low frequency feedback by an emitterresistor is limited. The noise suppression isalready nearly maximal for an emitter resistorequal to the absolute value of the totalimpedance of the base circuit.

In theory, the effect of transconductancefluctuations could be reduced by high fre-quency resistive feedback in the sources oremitters. This didn't work in practice, prob-ably because of the phase lag and signalleakage to ground caused in combination withthe parasitic capacitances.

It is often assumed that fets produce moreUf noise than bipolar transistors. But ourexperiments showed the lowest phase noisewas consistently achieved using fets. Apartfrom the inherently lower high frequencynoise of fets in oscillator circuits, the lowerphase noise could also be caused by the weakdependence of transconductance on draincurrent, which reduced the effect of Uf noise.Furthermore, bipolar transistors with low IAnoise often have a high base resistance and aretherefore not usable in v.h.f. oscillators.

Other sources of Uf noise are the transistorproviding the tail current to the differentialamplifier and the amplitude control circuitdriving it. Tail current fluctuations causeamplitude noise, which is also converted intophase noise. Experiments showed that ingeneral the lowest phase noise was obtainedby shorting the low frequency tail currentvariations with a large electrolytic capacitor.Only if the oscillator transistors themselvesproduced a large Uf noise, was it favourable tomake the amplitude control loop fast, so thatthe large amplitude noise of the properoscillator was suppressed.


The voltage dependency of the junctioncapacitances causes a.m.-to-p.m. conversion.The non -linearity of each junction capaci-tance should therefore be compensated by thenon -linearity of another one at which the r.f.voltage is equal. but in antiphase. The gate -

drain capacitances of the oscillator transistorsare automatically linearized, since they areanti -parallel.

The gate -source capacitances are in anti-series, and thanks to the compensation capa-citor C's their voltages are opposite. Theelectronic tuning of the oscillator is accom-plished by two matched varactors in anti -

series, where any asymmetry in parasiticcapacitances should be compensated.


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The oscillator phase noise is inversely pro-portional to the resonator power, which inturn is inversely proportional to the resonatorimpedance, which should thus be made as lowas possible. There is, however, a bound belowwhich decreasing the resonator impedancedoes not improve any more or even deterio-rates the oscillator c.n.r. This is caused byseveral factors:

- At too low a value of the resonator impe-dance the oscillator transistors can nolonger provide sufficient output power.

- The I/f corner frequency of transistors in-creases with drain or collector current.

- Due to the base resistance of bipolar transis-tors, the equivalent input noise voltagecannot be decreased below a certainthreshold and will even increase when thecollector current gets too high.

Then there is the practical problem of decreas-ing the resonator impedance while keeping asufficient electronic tuning range because thecapacitance variation of v.h.f. varactors is

limited. The impedance could be transformeddownward by coupling the resonator via a tapto the oscillator circuit. This increases,however, the r.f. voltage to the varactors andso the a.m.-to-p.m. conversion.


The circuit diagram of Fig.5 needs littleexplanation. Oscillation frequency is deter-mined by k, C3, C4, Di and D2. Resistors R1and R2 provide low frequency feedback toreduce the noise and the input offsetvoltage of the differential amplifier. Theiroptimum value is a compromise between I.1.feedback and amplitude control range. Cou-pling capacitor C9 has a low impedance at theoscillation frequency, but forms practically anopen circuit at low frequencies. Components

L2 and C5 prevent the r.f. noise of Tryentering the oscillator and C6 shorts thetransistor I.f. noise. The low -frequencydecoupling capacitors are connected to thepositive supply voltage to prevent modulationof the drain gate capacitances by noise on thepower supply.

Capacitor values of C1 and C4 are of theorder of some pF. They balance the voltagesacross the gate source junctions of the dif-ferential amplifier and across the varactors, toreduce a.m.-to-p.m. conversion. Besides, C1improves the frequency response of the ampli-fier.

To change frequency by a large amount 1.3,121 and R2 are the only components that needto be replaced. If the electronic tuning sensi-tivity is not critical, the oscillator can be tunedwith C1 over more than one octave.


The phase noise of the oscillator of Fig.5 wasmeasured using several types of transistors inthe differential amplifier. The place of the tapon the resonator coil and the amplifier tailcurrent were experimentally optimized forlowest phase noise. The results are shown inthe table.

The Table shows that the lowest phase noise


o Amplitudecontrol

Fig.5. To change frequency by a logic current, the only components to be charged are L3 andR1, R2. As it stands, it can be tuned over an octave with C3.

can be obtained with junction fets. Besides.the phase noise of an oscillator with fetsturned out to be less sensitive to the place ofthe resonator tap and the amplifier tail cur-rent.

TABLE 1. Lowest phase noise obtained at oscillation fre-quency of 100MHz at 5kHz from the carrier for severaltypes of transistors in the differential,amplifier.

Transistor Remarks2N3823 v.h.f junction fetBF198 v.h.f. bipolarCA3127 v.h.f. bipolar arrayBCY59C low I/f noise bipolarBFR90 low noise widebandBFQ69 low noise wideband

£(5kHz) (d8c/H4-116-106- 105- 91- 80- 70

The phase noise of the oscillator with the2N3823, BF198 and CA3127 was close to thevalue estimated with equations 2 and 3. Thehigh noise of the BCY59C is probably due to itshigh base resistance. The extremely highphase noise obtained with the BFR90 andBFQ69 is caused by a.m.-to-p.m. conversionof amplitude noise generated by l/f noise. Byincreasing the speed of the amplitude controlcircuit, the phase noise was reduced to-90dBc/Hz.

References1. Dekker. A. P.: Approximate noise analysis of afeedback oscillator using a non-linear differentialamplifier, to be published in AEU (Electronics andCommunication. Fed. Rep. of Germany).2. Dekker, A. P.: Compensation of parasitic sourcecapacitance in a fet differential amplifier. Letters.vol.22, no.I7, 14 Aug. 1986. pp.885-886.

A. P. Dekker is now with Nokia Telecom-munications, Espoo. Finland. having com-pleted this work at the Dr Neher Laboratoriesof the Dutch P7T. Leidschendam.

Non -switchingclass B amplificationFrom page 742

Under nulling condition. y = x + z. and afterelementary trigonometry:

132 = A' +

e = arctan (C/Al.

Now as only the output and the error signalare recorded. substitute A2 = 132 - C". Sofinally

e = arctan

Appendix 2 - Experimental amplifierTo eliminate influence from other distortionmechanisms as much as possible carefulcircuit design and layout were needed. Sepa-rate power supplies for the voltage gain stageand power stage were used and high currentground was separated from the signalground (see ref. 131. Test equipment groundwas connected to the input signal groundexcept for Fig. 8 recording, where the wholetest set-up was floating and the test amplifier"live" output was connected to the transientrecorder ground.

The voltage gain stage was designedaround a high performance operationalamplifier to simplify control over the open -loop bandwidth and gain, which were chosento represent typical values found in modernpower amplifiers.

Bias control was designed to be variableover a wide range to achieve requirementsfor class B and class A bias. The circuit mustbehave as a symmetrical low -impedancevoltage source for the output stage. ClassNSB operation was achieved by opening thecontacts of Sla and Slb and adjusting thequiescent current to the same value as theone chosen for class B operation. Class Aquiescent current was set to three amps.


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Modelling Yagi antennasA suite of Pascal programs calculates the gain, terminalimpedance, current distribution and radiation pattern of

moderate -size Yagi-Uda antennas for any geometry, elementthickness and operating frequency.

In any antenna problem one is presentedwith a piece of metal in space with somekind of transmission line connected to it.

In the metal there will be currents flowing,and in the space surrounding it there will beelectric and magnetic fields. These may bethe result of a signal fed via the transmissionline, or the result of an incident field from adistant transmitter; in either case the cur-rents and the fields are unknowns whichneed to be found.

Maxwell's equations give the informationrequired to proceed. Firstly they allow cal-culation of the electric field anywhere inspace resulting from a specific current dis-tribution. Secondly, they require that thevalue of the total electric field tangential to aconductor is zero. The conductor can bethought of as providing a short circuit to theelectric field. From these two conditions itfollows that if the current distribution on theantenna is known and the tangential electricfield is calculated anywhere on the antennasurface. then we will get minus the incidentfield.

In this form the problem becomes that offinding a function of space which, whencertain mathematical operations are per-formed on it. give a specified answer. Oneway of tackling this is to approximate theunknown current function by a large num-ber of point currents of unknown amplitudescattered over the metal surface. Clearly, ifan infinite number of points were taken, theactual current could be represented exactly.But a sufficiently large number will give areasonable approximation. Suppose alsothat instead of insisting that the field is zeroeverywhere on the metal, we insist that it bezero on a large number of selected testpoints scattered over the surface. Thesepoints could be, but do not have to be, thesame as those at which the point currentswere located. One could not evaluate thefield at each test point resulting from eachpoint current source and set each one tozero. This would result in a set of simul-taneous equations from which the ampli-tudes of the point current sources could becalculated. The value of the current betweenthe points could be found by interpolation.Thus the problem is solved.

In practice this method, known as pointmatching, will work if the number of pointsis high, which means that a very large arrayof simultaneous equations has to be solved,resulting in the requirement for much com-puter storage and processing, and the likely-hood of significant rounding error.


The method can be improved by usingother approximations for the current. Sup-pose, for example, that the current on a wirewere expressed as a truncated Fourier series.Suppose also that instead of using testpoints, weighted averages of the field arecalculated over areas of the antenna and setto zero. The result of evaluating the simul-taneous equations would then be the Fouriercomponents of the current from which thecurrent anywhere on the metal could beevaluated. By doing this, accurate results areobtained with smaller systems of equations,but the calculation of each coefficient of thesimultaneous equations becomes morelaborious.

The way in which the current is expressedas a combination of known functions, suchas impulse functions or trigonometricalfunctions in the above examples, is referredto as expanding the current in a set of basisfunctions. The way in weighted average ofthe resulting field is taken is referred to as atest function. Clearly we have completefreedom as to what functions to use, and intheory they will all give the same answer. Inpractice, it is crucial that a good choice ismade; the penalty is a great deal of computa-tion and an inaccurate answer.

In the computer programs described, thebasis functions and the test functions are thesame. Each wire on the antenna is dividedinto segments, and the current in eachsegment is approximated by a suitable func-tion. The greater number of segments speci-fied for each wire, the more accurate will bethe answer, and the greater the computationtime. The points at which the antenna isconnected to a transmission line must be inthe centre of a segment. In the usual case ofcentre feeding this is no disadvantage. It isusually desirable, for best efficiency, tospecify more segments on the driven ele-ment than on those elements towards theends of the array. This is because greaterinaccuracy can be tolerated on those ele-ments carrying little current before thecalculated parameters are unduly affected.


Analysing any radiating structure consistsessentially of calculating the currents in theconductors and the fields surrounding themfor a given excitation. This excitation can bea current or voltage generator as in the caseof a transmitting antenna, or an incidentfield as in the case of a receiving antenna.

If the current distribution is known every-

where on the structure then it is compara-tively easy to determine the resulting scat-tered fields anywhere in space. This is doneby evaluating the following integral which isderived from Maxwell's equations:

Es(r)=1 (V2 + k2) G (r,r') (r') d3f' (1)

where Glr,r. I -expk( r - r')Ir-r'I

k= 27r/x

Determining the currents for a givenincident field, however, is not so straightfor-ward. To do this, use the fact that at thesurface of a perfect conductor the tangentialcomponent of the total electric field must bezero. Any incident field induces a voltageacross the conductor, and the resultingcurrent produces a scattered field whichexactly cancels the incident field on theconductor's surface. Since currents can onlyflow on conductors it follows that anywherein space the scalar product of current densityand the total electric field is zero. That is,

(E,(r) + Es( r) 1.1(r) = 0 (2)

where E, is the incident electric field and E,is the scattered electric field. Take thescalar product of both sides of equation 1with J(r) and substitute equation 2 intoequation 1:

i(V2+K2) (G(r.r1.110)..1(r)d3r'

= -E,(r).J(r) (3)

and the problem is to find a function J(r)such that this equation is satisfied for allvalues of r. Once we have managed to findsuch a function we know by the uniquenesstheorem that it is the correct solution. Acommon method of solving such equationsis the method of moments or weightedresiduals, a special case of which is used inthe computer program Calerkin's method.

The first stage in this method is to expressthe unknown current function J(r) as aseries of known basis functions .15(r):


J(r) = 141,(r)(4)

Any permissible function J(r) can be repre-sented by an infinite number of coefficients


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as provided that the functions 15(r) form acomplete set of functions that are non -zeroonly on the surface of a conductor. In theory,any such set can be used in the calculationbut, as we shall see, some choices yieldresults more quickly and more accuratelythan others.

A simple way of arriving at a set of basisfunctions which illustrate the technique isto divide the conductor surface into a largenumber of small areas. On each area therewould be one and only one non -zero basisfunction. Eact basis function would be non-zero on one and only one area where it wouldhave a value of unity. As the number of areasinto which the surface is divided increases,the real current distribution is more closelyapproximated. Such a set of basis functionswould be appropriate for a solid metal bodybut there are better sets available for a wireantenna.

Substitute equation 4 into equation 1 toget the following expression for the scatteredfield:

f (v2+ asG1r,r'1.1sle Id3r' = (5)

Since the basis functions are non -zero onlyon the surface of the conductors, multiplyboth sides of equation 5 by each of the basisfunctions, integrating over all space andmaking use of equation 2, gives


f( V2+ k2).as f Clr,r'11,(r)d3r d3r'

= -f 1,(r) d3r

r = 1 _cc. (6)

This is an infinite set of simultaneous equa-tions for the infinite number of unknowncoefficients, as, which determine the currentdistribution on the structure. In practice wetake a finite number of basis functions andignore the effect of the higher order terms ofthe sum.

With a good choice of basis functions, astends rapidly to zero as s increases so thatthis approximation will not cause significanterrors. For example, if the first term in theseries happened to be the actual distributionthen all the terms except the first would bezero. Conversely if the functions are badlychosen and the basis functions are verydifferent to the actual current distribution.then a large number of terms must beretained with the consequent increase ineffort, rounding error and the likelihood ofnumerical instability.

In fact, if we had multiplied equation 5 byany set of test functions which are non -zeroonly on the conductors then we would endup with a valid set of simultaneous equa-tions. If in addition the set of functions werecomplete, we could equally well proceedwith this new set of equations.

The choice of test functions, like thechoice of basis functions, is largely a matterof educated guesswork and experience. Thecase where the basis functions and the testfunctions are chosen to be the same isknown as Galerkin's method. For the prob-

2, 2, 7.

Fig.1. A single wire showing three overlap.ping piecewise sinusoidal functions. Cur-rent flowing in the wire is approximated bya linear combination of these three func-tions. The accuracy of the approximationcan be improved by using a greater num-ber of these basis functions.






Fig2. E field at the point (Z,c) due to apiecewise sinusoidal current in the sectionof wire lying between points (z1,0) and(z3,0) is calculated using equations 9 and10.

lem under consideration (as well as manyothers) this choice leads to an efficientformulation.

Once a set of basis functions is decidedequation 6 can be solved, allowing calcula-tion of currents and fields in all space.


The basis functions appropriate to a Yagiantenna must, from inspection of thegeometry, have the following properties:they must be zero everywhere except on thewires and they must fall smoothly to zero atthe ends of the wires.

Simple functions which have these prop-erties are the following:

sin(kiz- WI)js(z', sin(k1s/2)

on wire s

= 0 elsewhere

where Is is the length of the 5th wire z is thedistance measured from the centre of thewire.

This approximate current distribution iswidely used in published tables for the selfand mutual impedance of dipoles and forarray antennas. In fact this approximation isonly good if the wires are of the order of ahalf -wave long. For this assumed currentdistribution function, equation 5 becomes aset of simultaneous equations of order Nwhere N is the number of wires. Solution ofthis set would give the magnitudes of thecurrents on each element. Results for para-meters such as gain and impedance based on

this assumed current would not be accurate.but would give a rough idea.

A better approximation can be obtained byusing more than one basis function for eachwire, such as the following

sin k lz - zr, 11.1(z) - < z < zrsin k (zp - zis_11

sin k - z) z < z <sin k - zd P


where p=1 N zp = pl/In+1) - 1/2, I is thelength of the eh wire, and N the number ofbasis functions on the sth wire.

Here we are approximating the current onthe sth wire by dividing it into N overlappingsegments and specifying that each of the Nbasis functions are non -zero only on onesegment.

These functions are shown in Fig.1 for onewire. They form overlapping sinusoids thatgo to zero at the wire ends, as required by theboundary conditions. If N is chosen to be 1then we recover equation 7. As N is in-creased, the actual current can be betterapproximated, yielding a more accurateanswer at the expense of greater computa-tion.

We are at complete liberty to specify adifferent number of basis functions on differ-ent wires. Indeed, it is desirable to a specify alarger number of basis functions for thedriven element than for the others, especial-ly when calculating terminal impedance.

However, there is no guarantee that thesolution will improve as the number of basisfunctions is increased. Although we areensuring that the boundary conditions arebeing satisfied on the average in moreplaces, we are saying nothing about how wellthey are satisfied in any one place. It is quitepossible for the value of the calculated totalfield to oscillate widly about zero from placeto place and still satisfy equation 6. But inpractice, for sensibly chosen basis functions.Galerkin's method is well behaved.

Experience has shown that the piecewisesinusoidal basis functions given in equation8 are well suited to the Yagi problem. Inaddition. with this choice of basis functions.the integral of equation 1 is available as in asimpie closed form which can be expressedin cylindrical coordinates as follows:

E.expl-jkRi )


expl-jkR2Isin kl exp 1-jk123)

R2sin2(kV1) R3sin (kl/2)1


j30 {(z- lexp-jkR+Ed, -

(I) Rizsin (kI/2)

+ -R2sin-lk1/2)

lz -z3exp-jkR3 1R3sin(k1/2) f


where the dimensions are defined in Fig.2.


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Fig.3. Polar radiation patterns of a 30MHz seven -element Yagi using wires of radius25mm.

28.5MHz- -









In the case of a Yagi all the elements areparallel and so we need only concernourselves with the z -directed field. Notheoretical difficulty would prevent exten-sion to elements placed at any desiredorientation if required.

Substituting equation 9 into 6 gives


fJr dz = f Ezi.1dz (11)

p S1,,r2

for q = 1...number of elements r =1...number of basis functions on the qthwire, and where 1, is the length of the rthsegment on wire q, Ez, is given in closedform by equation 9.

The integral is the mutual impedancebetween the segments rq and sp. Integrationcan be carried out numerically withoutundue trouble. The problem is now reducedto the evaluation of a number to calculatethe values of the coefficients and hence theapproximate current on the elements.


30 5MHz 31MHz We now have a computation method whichallows us to find the currents on a Yagiantenna for a given incident field. To calcu-late useful parameters such as the gain andthe terminal impedance, it is necessary toconsider the incident field produced by atransmission line connected to the driveelement.

Various models for the feed point of anantenna have been used and they vary inaccuracy and complexity. A simple but effec-tive one is the delta gap. Here we assumethat the driven element has an infinitesimalgap at the driven point. Across this gap isapplied a voltage source such as a transmis-sion line. With this model, the integral onthe right hand side of equation 11 becomesequal to the magnitude of the voltagesources times the value of the test functionat the driven point.

tion of a real feed system, but it does giveClearly this model is only an approxima-

,C.- good answers and it is widely used.v Once the currents have been calculated by

means of equation 11, the terminal impe--dance is immediately given as the drive

30MHz voltage divided by the current in the drivensegment. To calculate the gain we need toknow the magnitude of the radiated field farfrom the antenna. For large distances equa-tion 9 and 10 become

j30 exp -jkRisin (kI/2)

30 5 M H z 31MHz exp (-1kR) sin kl exp -jkR31sin2(k1/2) sin (kI/2) I (12)

Fig.4. Polar radiation patterns of a 30MHz seven -element Yagi, this time with wires of10mm radius. E,b = E, tan (1) (13)


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where F is the angle of elevation of thepoint of observation.

The gain is given by

(iEz12 + iEri2) Zo4 Tr P,

where Po, is the total power delivered to theantenna.


The program is split into three parts, partlyfor reasons of space and partly from conveni-ence. It is possible to run the programs onmost computers which have a Pascal compil-er with very little change. The only machine -specific part of the program is the graphicsroutines which are written in Z80 machinecode. It is likely that equivalent graphicslibrary routines would be available on othermachines.

First of all, the program GETWIRES takesinformation from the keyboard about thegeometry of the antenna to be analysed. Itthen produces a file which is used by the nextpart. This avoids the need to type in thegeometry each time an analysis is to be done.

The actual analysis is carried out in theprogram YAGI which calculates the currentson each segment for a given excitation andfrequency. The radius of the wire used can bespecified, as can the number of segmentsinto which to divide each wire. In this waythe accuracy of the solution can be tradedagainst computer time.

The main procedures in the programperform as follows:GETIMP calculates the mutual impedance be-tween segments of specified length andposition at a given frequency and with theassumed piecewise sinusoidal current dis-tribution. This is carried out by numericallyevaluating the integral in equation 11. Func-tion F is the integrand, and the integral iscarried out by function cAusin by means ofthe gaussian quadrature method.CLUFAC and CLUSOLVE solve the set of complexsimultaneous equations represented by acoefficient matrix A and a vector B, the resultis given in a vector X.

UOSELF calculates the mutual impedance be-tween all segments on a particular wire andsets the appropriate elements of the matrixzMAT. Because all the segments on any givenwire are the same length and are placed

contiguously, only one calculation per seg-ment need be performed.

MOTHERS calculates the mutual impedancebetween all segments on a given wire with allsegments on another given wire and sets theappropriate parts of matrix ZMAT. Since, ingeneral, the segments on different wires canbe of different lengths, each value is workedout separately.

SETURWEN requests information about theexcitation of the antenna and stores theinformation in the structure URN.

DOANT calculates on each segment for aspecified excitation and frequency and calcu-lates the terminal impedance. For a two -element array the mutual impedance be-tween the wires is also calculated.

oirrcuRR saves the calculated currents for useby the program PLOTFIELD.

PLOTFIELD takes the information calculated byvac! and produces a polar of the far -fieldradiation pattern. By means of a screen copyroutine, the diagrams together with annota-tions can be printed onto a dot matrixprinter.


To show the sort of results which can beobtained from the programs two different

25mm !lows ..

10mm r00.u5

295 30FRETJEV.r

Fig.5. Gain as a function of frequency forthe antennas of Figs 3 & 4.

Fig.6(a) (below, left). Resistive part of theterminal impedance as a function of fre-quency, showing the effect of varying thewire radius.

Fig.6(b) (below, right). Reactive part of theterminal impedance of the seven -elementarray as a knction of frequency for wireradii of 25 and 10mm.


60-70- \


60- Z 20-/


ri; 0


25mm radius -20-z

40-- F

..10mm radius-60--7030

285 29 295 30FREQUENCY (MHz)

3015 31

Yagis have been analysed. Figures 3 and 4show a series of polar diagrams for a seven -element Yagi with wire thicknesses of 25mmand 10mm respectively. Spacing is 3m.Reflector length 4.75m, driver length 4.55mand director lengths are 4.39m. Notice howthe radiation pattern breaks down as thefrequency approaches 31MHz.

Figure 5 shows gain plotted against fre-quency for this antenna and Fig.6 showsterminal impedance versus frequency. Theeffect of varying the element thickness canbe clearly seen. This antenna was analysed byThiele' for a frequency of 30MHz and wireradius of 25mm using a reaction matchingtechnique. The results for gain and impe-dance are in good agreement.

These results, especially the plots againstfrequency, are not quick to obtain and anovernight run is likely to be the norm. Theprograms have, however, been designed torun with little intervention so that thisshould not present a great problem.


Any moderately -sized array of parallel wirescan be analysed by the programs as de-scribed. But it is possible to extend theprograms to cope with skew wires or bentwires such as a folded dipole or a cubicalquad. With different basis functions it wouldbe possible to analyse the effects of metalstructures in the vicinity of the antenna, asthe case of vehicle -mounted antennas.

References1. Antenna Theory and Design, by Stutzman and

Thiele, Wiley, 1981, p226.

2. Radio Communication Handbook, Radio Socie-ty of Great Britain. 1969. p14.22.

Enquiries about software described in thisarticle should be addressed to the author atCadney, Highfield Road, Whiteshill. Stroud,Gloucester GL6

Chris Railton is at the University of Bath.working for a Ph.D. on boxed microstripcircuits.



25mm radius


10mm radius


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DECCA 80 16 COLOUR monitor. RGB input.Little or hardly used manufacturer's surplus enables us to offer this specialconverted DECCA RGB Colour Video TV Monitor at a super low price of only£99.00. a price for a colour monitor as yet unheard of Our own interfacesafety modification and special 16 high definition PIL tube coupled with theDECCA 80 series TV chassis give 80 column definition and quality found onlyon monitors costing 3 TIMES OUR PRICE. The quality for the price has to beseen to be believed. Supplied complete and ready to plug direct to a BBCMICRO computer or any other system with a TTL RGB output Other featuresare imerna! speaker, modular construction, auto degaussing circuit. attractiveTEAK CASE. compact dimensions only 52cm W a 34 H a 24 D. 90 dayguarantee Although used units are supplied in EXCELLENT condition.ONLY £99.00 + CarriageDECCA 80 16 COLOUR monitor. Composite video input. Same as abovemodel but fitted with Composite Video input and audio amp for COMPUTER,VCR or AUDIO VISUAL use ONLY £99.00 + Carr.REDIFFUSION MARK 3, 20 COLOUR monitor. Fitted with standard 75 ohmcomposite video input and sound amp This large screen colour display is idealfor SCHOOLS. SHOPDS. DISCOS CLUBS and other AUDIO VISUAL appli-cations Supplied in AS NEW or little used condition ONLY £145.00 + Carr

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All prices quoted are for U.K Mainland. paid cash with order in Pounds Sterling PLUS VAT. Minimum order value E2.00.Minimum Credit Card orderE/0.00 Minimum BONA FIDE account orders from Government Depts.. Schools. Universities andestablished companiesE20.00. Where post and packing not indicated please ADD C 1.00 + VAT. Warehouse open Mon -Fri9 30-5.30.Sat 10.30-5 30 We reserve the right to change prices and specifications without notice. Trade. Bulk and Export

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Made to the veryhighest spec the TECSTARWRITERFP1500-25 features avery heavy duty die castchassis and DIABLOtype print mechanismgiving superbregistration and printquality Micro -processorelectronics offer fullDIABLO/OUME command comparability ana turf con ro via CPM WORDSTARETC. Many other features include bi-directional printing, switchable 10 or 12 pitchfull width 381 mm paper handling with up to 163 characters per line. friction feedrollers for single sheet or continuous paper. internal buffer, standard RS232 serialinterface with handshake. Supplied absolutely BRAND NEW with 90 day guaranteeand FREE daisy wheel and dust cover Order NOW or contact sales office for moreinformation Optional extras RS232 data cable £10.00 Tech manual £7.50 tractorFeed £140.00 Spare daisy wheel £3.50 Carriage 8 Ins (UK Mainlandl 110 00

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DIY PRINTER MECHBrand New surplus of this professional printer chassis gives anoutstanding opportunity for the Student. Hobbyist or Roboticsconstructor to build a printer - plotter - digitiser etc. entirely to theirown specification. The printer mechanism is supplied ready built.aligned and pre tested but WITHOUT electronics. Many featuresinclude all metal chassis, phosphor bronze bearings. 132 characteroptical shaft position encoder. NINE needle head. 2 x two phase 12Vstepper mctors for carriage and paper control. 9.5 Paper platten etcetc. Even a manufacturer's print sample to show the unit's capabilities"Overall dimensions 40 cm x 12 cm x 21 cm.Sold BRAND NEW at a FRACTION of cost ONLY £49.50 + pp £4.50


Industry standard, combined ASCII110 baud printer, keyboard and 9hole paper tape punch and reade-Standard RS232 serial interface.Ideal as cheap hard copy unitor tape prep. for CNC and NCmachines TESTED and in goodcondition. Only f 250.00 floorstand £10.00. Carr & Ins £15.00.


Compact ultra reliable quality built unitmade by the USA EXTEL CorporationOften seen in major Hotels printing up tothe minute News and Financial inform'ation. the unit operates on 5 UNITBAUDOT CODE from a Current 100P,RS232 or TTL serial interface May beconnected to your micro as a low costprinter or via a simple interface and filterto any communications receiver toenable printing of worldwide NEWSTELEX and RTTY servicesSupplied TESTED in SeCo id handcondition complete with DATA, 50 and75 baud xtals and large paper roll.TYPE AE11

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Due to our massive bulk purchasing programme. which enables us to bring yoc thebest possible bargains. we have thousands of ICs. Transistors. Relays. Caps. PCBs.Sub -assemblies. Switches etc etc surplus to OUR requirements Because we don'thave sufficient Stocks of any one item to include in our ads we are packing all theseitems into the BARGAIN OF A LIFETIME Thousands of components at giveawayprices Guaranteed to be worth at least 3 times what you pay Unbeatable value andperhaps one of the most consistently useful items you will every buy"' Sold byweight

2.5kIs £5.25 + pp £1.25 5 kls £6.90 + £1.8010kIs £11.25 + pp £2.25 20kls £19.50 + pp £4.75


A massive purchase of these desk topprinter terminals enables us to offer youthese quality 30 or 120 cps printersat a SUPER LOW PRICE against theiroriginal cost of over 11000 Unitcomprises of full OWERTY electronic,keyboard and printer meth with printface similar to correspondence qualitytypewriter Variable forms tractor unitenables full width - up to 13 5 120column paper. upper - lower casestandard RS232 serial interface internalvertical and horizontal tab settingsstandard ribbon. adjustable baudrates. quiet operation plus many otherfeatures Supplied complete with manualGuaranteed working GE30 £130.00.GE1200 120 cps £175.00Untested GE30 £65.00 porstand £12.50 Carr 8 Ins i '


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PioneersW. A. ATHERTON

7. Alexander Graham Bell(1847-1922):

speech shaped current

What do the following items have incommon: the National GeographicSociety, the American magazine

Science, aircraft ailerons, and sheep withfour nipples? No. it's not Trivial Pursuit. Allwere steered into existence by the same man,the inventor of the telephone.

To most people the telephone is one of thegreatest inventions of all time. Yet oneAmerican newspaper reporter wrote "It is aninteresting toy . . . but it can never he of anypractical value."

That reporter was not alone in dismissingthe new invention. A British official thoughtit might prosper in the colonies hut not inBritain since "we have an abundance ofmessenger boys". And the great WesternUnion Telegraph company rejected an offerto buy the patent. "Bell's profession is that ofa voice teacher." they observed. "Yet heclaims to have discovered an instrument ofgreat practical value in communicationwhich has been overlooked by thousands ofworkers who have spent years in the field."

The patent Western Union turned downwas one of the most lucrative ever issued. forthe commercial success of the telephone wasas immediate as it was dramatic. AlthoughBell at first gave lectures and demonstra-tions to raise much -needed cash (reservedseats cost 50 cents and the first profit was$149) the success of the telephone made himand his assistant, Thomas Watson. financial-ly secure by 1881. The telephone was by thena mere five years old.

Western Union did, however, get onething right in their assessment of Bell: hewas indeed a teacher of the deaf.

Born in Edinburgh on March 3. 1847. hewas christened Alexander. On his eleventhbirthday he decided he would like a secondChristian name and chose Graham. He andhis two brothers inherited a family traditionof teaching elocution. His grandfather hadpractised in London and his father was theinventor of a phonetic alphabet called VisibleSpeech. Both Bell's mother and wife weredeaf. Helping deaf people learn to speakbecame his main career.

Bell received his early education from hismother and he became an accomplishedpianist. At ten years of age he started school.

By the time he entered University College.London at 20, he had taught elocution atElgin. Edinburgh and Bath.

At university he studied anatomy andbiology. But before that, in a letter to hisfather. he had written up his first scientificresearch, on the resonant pitches of mouthcavities. As a result of this he was introducedto the work of Helmholtz and gained his firstknowledge of electricity.

His brothers died early from tuberculosis.Partly fearing for the health of their remain-ing son, the family quit Britain for thehealthierclimateof Canada on August 1.1870.

In Quebec. Bell taught his father's VisibleSpeech to deaf pupils and began to teachteachers of the deaf. In 1873 he wasappointed professor of vocal physiology atBoston University. Nine years later he be-came a US citizen, and very proud of the facthe was too.


Work with the deaf turned Bell's intellect toall things related to the human voice. Insearching for teaching aids he came acrossthe phonautograph. a device with a conicalmouthpiece and a stretched membrane

which vibrated in response to the voice. Themechanical vibrations were conveyed to astylus which traced the wave pattern of thevoice on to a moving piece of glass blackenedwith soot.

These and other attempts to make a visualrecord of a human voice for use as a teachingaid for the deaf were crucial to the inventionof the telephone. The step from a mechanicalrecord of voice waves on blackened glass toelectrical waves in a wire was the mark ofgenius. But it did not come in a flash.

For several years Bell had been activelyinterested in telegraphy and a parallel prob-lem with which he now wrestled was how touse an intermittent electrical current totransmit musical tones via the telegraph.This he thought possible if the vibrations ofthe air could he somehow reproduced in anelectrical current.

In the summer of 1874 he visited hisfather's home in Brantford, Canada. takingwith him a human ear provided by theHarvard Medical School. The idea was to usethe ear and the small hones of the ear tomake an improved phonautograph: a pieceof hay acted as the stylus. The human -earphonautograph worked!

If the relatively massive hones of the ear


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This instrument was used to transmit the first speech sounds electrically in 1875. Theparchment diaphragm is attached to a magnetized metallic reed. Piture from AT&T.

could he vibrated. thought Bell. why not asmall piece of steel? The basic concept of thetelephone now crystallized. though its prac-tical achievement was still far away. When apractical realization came we can he thank-ful that the mouthpiece did not need ahuman ear cut from a corpse.

Whilst continuing his work with the deafin Boston. Bell had for some time beenworking on ideas for a multiple telegraph.one which would enable simultaneous sig-nalling of many messages to take place alonga single line. By this time he had met a youngmachinist. Thomas A. Watson. and towardsthe end of 1874 they worked together atBell's idea for multiple telegraphy. In thatsame year Bell explained his telephone ideato the aged Joseph Henry. seeking his adviceas to whether to publish the idea so thatothers could work at it or to finish it himself.Henry told Bell to finish the work himself.When Bell confessed that he did not have theelectrical knowledge needed Henry's advicewas blunt: "Cet it!"

Bell meantime had obtained financialhackers: not for the telephone. but for themultiple telegraph, for which his hackershad greater hopes. (When the telephonebecame a success Bell himself insisted that ithe part of the agreement.)


With his experience of the phonautographand his mental concept of the telephone, alittle accident with the multiple telegraphequipment showed Bell how to achieve hisdream of electrical speech.

The multiple (or harmonic) telegraph wasto work as follows. At the transmitter andreceiver there were tuned vibrating reeds. Areed at the transmitter tuned to a frequencyft could. according to the theory. send apulsed signal which would only he detectedby a reed also tuned to fi at the receiver.

Several reeds tuned at different frequencies(f1. f,. f3. etc) should enable several pulsedsignals to he transmitted simultaneously.

On June 2. 1875. in the middle of a bakinghot afternoon. Watson and Bell were retun-ing the reeds when one of Watson's trans-mitter reeds stuck. The adjustment screwhad been screwed too far. To restart Watsonplucked it and Bell, at the receiver, gave aloud shout.

Held too hard, the reed had failed tointerrupt the current and had produced acontinuous sine wave instead. Bell recog-nised the answer to his dreams. The rest ofthe afternoon and evening were spent re-peating and repeating the discovery.

By the time they parted Bell had sketchedout a diagram of the first telephone andbegged Watson to try to build it ready for thenext evening. "And. as I studies the sketchon my way home to Salem on the midnighttrain." Watson recalled. "I felt sure I could doso." He did. The next evening the first faintsounds (not speech) were transmitted andreceived. As yet unintelligible they provedBell's basic idea.

During the ensuing months. work on themultiple telegraph took enforced priorityover the telephone. along with ill health.personal crisis. and teaching duties. AnAmerican patent covering the telephone wasallowed on Bell's 29th birthday. March 3.1876. It was actually issued four days later.

On the evening of March 10. intelligiblespeech was achieved using a 'liquid' trans-mitter and a tuned -reed receiver. In the newtransmitter, designed by Bell and built byWatson. a metal wire attached to a dia-phragm was dipped into acidulated water.The water and wire were part of the electricalcircuit. As sound waves vibrated the di-aphragm. the wire moved up and down inthe liquid and so varied the resistance of thecircuit. The telephone had arrived.

New transmitters and receivers followed.

An early British instrument, of about 1890:a wall telephone of the National TelephoneCompany. Picture from British Telecom.

some using liquids and some employing therelative movements of magnetized coils andpieces of iron. These were demonstrated atthe Centennial Exhibition in Philadelphia onJune 25. 1876 (the day of Custer's last stand)and impressed all who saw them. LordKelvin. who was one of the technical judges.ran the 100 -yard length of the gallery fromthe receiver to the transmitter to congratu-late the inventor.


Watson. after some persuasion. resigned hiswell -paid full-time job to take up full-timework on the telephone. He received a tenthshare of the patent. In November. using yetanother new design. successful tests wereconducted between Boston and North Con-way in New Hampshire using a railwaytelegraph wire. a distance of over 100 miles.

A company was formed in July 1877 two orthree months after the first regular tele-phone lines opened in Boston. Other Bellcomnanies followed swiftly for variousreasons. and a reorganization in 1880 cre-ated the American Bell Telephone Company.

Western Union meanwhile had set up incompetition after the principle of the tele-


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phone had become known. Bell sued forinfringement of his patents and won. TheBell patents were repeatedly defended in thecourts, on about 600 cases, before theSupreme Court eventually upheld all Bell'sclaims.

Bell meanwhile had married Mabel Hub-bard. one of his private pupils and thedaughter of one of his financial backers, onJuly 11. 1877. The marriage was long andhappy despite the loss of two of their fourchildren at birth. In August they sailed toEurope to promote the telephone, leavingWatson in charge for over a year. At the timeof the wedding a couple of hundred tele-phones were in operation.

By 1881 both Bell and Watson had movedon to other interests.

Bell continued his absorbing interest inteaching the deaf to speak well. His interestin hereditary deafness led him to studies oflongevity and breeding. In 1909. after 20years' selective breeding, he had a flock ofsheep with four or more milk -producingnipples rather than the usual two! Thereinlies a tale in itself.

In 1880 France awarded Bell the VoltaPrize of 50 000 francs. This he used toestablish the Volta Laboratory Association inWashington to work with the deaf. Two yearslater he conceived the idea for the journalScience which began publishing in 1883. Inits first eight years Bell and his father-in-lawsubsidized the journal to the tune of around$100 000.

Bell also helped organize and finance theNational Geographic Society and was itspresident for several years. and he gave$5000 to establish the Smithsonian Astro-physical Laboratory.

For the last 25 years or so of his life one ofhis main interests was aviation. With a gift of$50 000, he founded the Aerial ExperimentAssociation under whose auspices some ofthe earliest flights took place in 1908. Belland the Association held the patent for thedesign of ailerons for wings and rudders.

He also invented a tetrahedral construc-tional technique known as space frame, triedto introduce the Montessori educationalmethod to America. and developed an in-terest in designing hydrofoil boats. One ofhis hydrofoils gained the world water speedrecord in 1919 at 70.86 miles per hour.

Amongst the honours Bell received wasthe freedom of Edinburgh (his birthplace).the opening of the first trans -continentaltelephone link between New York and SanFranscisco in 1915, and the naming of anisland after him.

After his death in 1922. at the age of 75. hewas buried in a rock tomb on top of amountain. Every telephone in North Amer-ica was silent for one minute during hisfuneral.

Next in this series of pioneers of electricalcommunication will be Oliver Heaviside.

Tony Atherton works at the IndependentBroadcasting Authority's engineering train-ing college in Devon. His book. From Com-pass to Computer. A History of Electrical andElectronics Engineering, was published byMacmillan in 1984.

68000 -familyPascal machineIf you need to decide which computer language to use foryournext industrial control system, one of the new breed of Pascal

compilers may be ideal.


pascal was designed as an easy -to -learnlanguage to teach students how towrite programs, which humble begin-

ning it shares with Basic but unlike thatlanguage, Pascal enforces the concept ofstructured programming. To someone whohas used Basic, Pascal may appear to bepedantic, it lacks a 'goto' statement forinstance, but its strength is that it forces theprogrammers to understand the true natureof the task before starting to write a pro-gram. This means that the program is

produced in the correct construction, if notin detail, the first time round as opposed to apoorly concieved core modified by layers of'goto' statements and extra modifications toget it to work. Even if the time taken to writein both forms is the same, the real costadvantage of Pascal is that the resultingprogram is self -documenting to a largeextent, which leads to easier and fastermaintenance.

One of the strengths of Pascal is itscomprehensive selection of data types avail-able to the programmer, which now encom-pass boolean, character (byte), enumeratedtype, integer, longinteger, hex, longhex,real, string, array, record, devices and files,and pointers. The string functions, so long aweak point in Pascal, have now been en-hanced to give similar performance to thosein Basic, which has always enjoyed powerfulstring operators.

Pascal has been limited by some of thesame problems as Bask in that it was onlyavailable in an interpretive form or withintermediate code output which producedslow executing programs. This tended topreclude control by the programmer as towhere variables were held: the compiler orinterpreter allocated space in the memory,usually via the stack, or optionally on areverse stack, the 'heap'. without any bear-ing on the wishes of the programmer. Forindustrial control, or for any applicationwhich wants to poke its nose outside theconfines of the operating system, it is essen-tial to be able to access absolute addresses inthe memory map to talk to i/o ports. This isnow possible in Pascal because the user can

specify how the variables are held; on thestack (by default), at an extended (absolute)address, program counter relative, definedin another module or, on 16bit processors,in a c.p.u. register.

A requirement for most programs is theability to perform simple operations on allrelevant classes of data without large proces-ing overheads; things like OR. EOR. AND. NANOand shift. This limitation is overcome in thelatest generation of Pascal compilers, whichcan produce compact 'romable' position -independent object code that is frugal onmemory and has a runtime library overheadproportional to the function used. To givefigures for one particular compiler, theOmegasoft 68000 Pascal compiler, typicalruntime overhead is between 1 and 3Kbytes,with a minimum of about 50 bytes and amaximum of 10K using every function anddata type: the compiler efficiency is about0.4 that of hand -coded assembler but theexecution speed is fast. This compares wellagainst a C compiler running on the sameoperating system; the code efficiency isabout the same and the Pascal programsusually execute faster. This is not intendedto show that Pascal compilers are 'better'than C compilers, simply that they arecomparable and that C code is not automati-cally the optimum solution.

Another development, which has becomemore common in the later compilers, is tosurround the compiler with a suite of utili-ties that make the task of converting theprogram into debugged object code mucheasier. In the example of Omegasoft Pascal,this takes the form of a easy -to -use linkagecreator which asks the user a series ofquestions about the physical properties ofthe hardware and produces a small assemb-ler program as a result. This sets all therelevant stack pointers for the main Pascalprogram and also produces a procedural filewhich will assemble and link all the neededmodules.

A type of utility that has become popular isthe interactive debugger, which will allowthe programmer to debug software at Pascalline level. to be able to breakpoint to a line


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Can now compile programs from inside theeditor so that syntax checking of a new piece ofcode is now very quick. Errors found by thecompiler in this mode are passed back to theeditor on a stack, and can be popped off thestack by an editor command to quickly movefrom error to error. Compiler now supports longreal types in theIEEE 64 -bit format and can support the 68881floating point coprocessor as a peripheral. A 'Pascal shell' provides a complete Pascalprogramming environment for each project Thiskeeps track of all the related files in a suite ofprograms so that when changes are made to onefile it it easy to recompile and link all the modulesback together with just a few keystrokes. It alsoallows considerable control over the recompila-tion: you can specify to recompile all filesmodified after a certain date and time, or afterthe date on a particular file. Only the files relatedto the task are kept inside the shell environmentso that the rest of the operating system 'clutter' isnot obscuring the work. All the Omegasoft utili-ties are catered for from inside the shell. It ispossible to edit a set of files. then tell the shell torecompile and load the debugger. leaving theuser ready to start debugging or recompile,assemble and link and produce 'romable' codefiles. An optimized 68020 version of the compilerwill support f.p.u. (68881 and 68882) directly onthe coprocessor interface with in -line code, andshould be available in July or August Source code of the pascal shell, linkagecreator. screen editor and runtime library areincluded for reference.

number, display or change variables byname, trace by line or by procedure. Themore sophisticated debuggers, usuallyfound on 16 or 32 -bit processor versions,will allow assembler modules to be added fordebug along with other Pascal modules, andpermit macro definitions of the debuggercommands. They may even have anassembler -level debug inside which willallow debug and disassembly of assember orPascal programs. A software tool with thiskind of capability is quite a large program inits own right, and a fully-fledged one maytake over 100Kbytes of memory space andassumes that the industrial i/o hardware is inits own memory map. As it takes so muchmemory to support all these features, thiskind of debugging is only found on the larger16/32bit processors and although eight -bitversions are available, the powerful featureshave been trimmed down to allow them to fitinto a 64Kbyte address space.

To give another example, this time Ome-gasoft's 6809 Pascal compiler, where thedebugger uses overlays to maximize the sizeof program it can debug; has no assemblerlevel phase and cannot support macros,though it can single-step, set breakpoints.examine and change variables. It takes about30Kbytes of memory which, when added tothe operating system leaves about 15 to20Kbytes for the program to be debugged.should allow room for between 100 and 400lines of Pascal, depending on the functionsbeing used. Many applications will fit intothis space, but if not then it is possible towrite larger programs as a series of modules.and debug the modules separately beforejoining them all together to produce thefinal object program.

For 16/32 bit processors the overhead of100K for the debugger in a developmentenvironment is not a problem as memory forthese systems is now relatively cheap. Ifdevelopment is done on a modular hardwaresystem such as VME, this may not be toomuch of a problem as the necessary func-

Inc udes




Object mod._


User data

and results

First introduced to the 6809 market in 1980, Omegasoft Pascal has been expanded andrefined, with major extension to the ISO level 0 standard that allow its use for industrialcontrol and other real-time applications. It is newly available from Certified SoftwareCorporation of California (RCS Microsystems in the UK) to run under OS -9, P -DOS,Versados and CP/M-86K operating systems.

tions can be plugged into the target systemso that in effect it is a development systemwith large amounts of ram and mass storage.After the debugging is complete the excessitems can be removed from the system. If thetarget system is a limited -function systemthat has been designed for a specific purposewithout room to accommodate the hostdebugger, a different approach is needed.and this is provided by a target debugger.

This technique was first used by DigitalEquipment Corp. for their 'Micropower Pas-cal' and has subsequently been adopted byother vendors. It involves writing a smallprogram, usually in assembler, to copy datafrom the target serial port to and from ramon the target system. The bulk of thedebugger now resides in the users host ordevelopment system, which will have massstorage and plenty of ram. and the programto be debugged is passed to the target via theserial port. When excecuted, this target.debug affords the user the same power as thehost debugger, but only requires a small

overhead in the target memory.Pascal has become an excellent tool for

writing software in the industrial controlenvironment. The standard ISO core com-piler with its large selection of data types andextensive intrinsic library functions hasbeen extended to permit easy access tohardware and to overcome some of itsprevious limitations. The result is that pro-grams can be written in Pascal. whichproduces clear and concise listing docu-mentation. that can be just as efficient andfast as any other compiler. Added to that arethe benefits of interactive debugging on ahost or target system and the extra utilitiesfor making stand-alone 'prommable' codeeasily. Could this he the language thatreaches parts of your control system thatother languages cannot reach?

William Stanley is Omegasoft product man-ager with RCS Microsystems of HamptonHill. Middx. tel. 01-9792204.


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High performance? they all say that.Ah yes, but. . . .

Image -10 has three 16 bit processors workingconcurrently for dazzling speedandImage -10 has a resolution of 768 by576 pixels for intricate detailandImage -10 has 256 on -screen colours givingphotographic quality.In fact Image -10 has all of therefinements asked of graphics intensiveapplications. Like hardware windows,hardware drawing, hardware zoom and pan,hardware character generation and hardwareblock moves. The only thing the cpu has to dois to run your applications.

Board Price £1295Image -10 includes:

* 68010 cpu * 82786 gdc* Floppy disc controller* Dual RS232 * Centronics

* Battery backed clock* 512K dram * 64K sram* Winchester disc controller

* Mouse * transputer ports* Stereo sound generator* 256K eprom


SYSTEMSVersatile, low cost, developmentsystems based on Micro Concepts'single board computer, Microbox 3.A choice of powerful disc operatingsystems is available including Os -9/68K, TRIPOS, and CP/M-68K

Features include:68000 microprocessor, 8MHz clock.512K dynamic ram. 64K static ram.128K epromOn -board graphics controller offers:80 column, 24 row, 16 colour text.640 by 480, 4 colour graphics.320 by 480, 16 colour graphics.Floppy disc controller.Winchester disc controller.Dual serial RS232 ports.Centronics printer port.Up to 48 lines of parallel input/output.Battery backed clock/calendar.I/O expansion capability.Double eurocard board format.

Hardware prices:Fully built and tested Microbox 3 singleboard computer £650System with dual 1M byte floppy discdrives £1195System with 20M byte Winchester andsingle floppy drive £1895


for allMSDOS OS -9 FLEX


Supports the following devices1802 809 80496502 8022 80806803 8039 87516808 80C48 63038021 8051 680280C35 8749 68HC058048 68000 80208050 6301 80358748 6801 8040Z80 6805 80C491805 68HC11 80856800 8031 Z86804 80C39

Extensive directives supportmodular, conditional andstructured program-ming. Powerful Macro Pre-processor, xref generator andoutput conversion utilitiesprovided.




PROGRAMMERPrograms the following devices:2508 2516 25322564 27(C)16 27(C)322732A 27(C)64 2764A27(C)128 27128A 27(C)25657(C)256 27(C)512 275132758 27011 2816A2817A 2864A 2825648Z02 52813 52132352833 68732 6876468766 8741 87428744 8748 87498748H 8749H 87518755 9761 CY7C282CY7C292 DS1225AT -ROM PC -ROM XT -ROM

No Personality Modules required.Controlled via RS232 interface.Accepts Intel, Motorola, Ascii-hexand binary data. Ultra -fast, fast andstandard programming modes.Low and high byte programmingsupported.Completely self contained butuncased. Price £295

All prices shown exclusive of VAT and carriage

Micro) Concepts 2 St. Stephens Road, Cheltenham, Gloucestershire GL51 5AATelephone (0242) 510525



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Video frame storeFast look -up table enables the unit to manipulate moving images

in real time for flicker -free special effects.

The frame store is a powerful tool forimage capture, but in its basic form ithas no facilities for real-time image

processing. Manipulation of images musttherefore be done entirely by the - hostcomputer.

The look -up table is a significant enhance-ment because it enables the real-time man-ipulation of pixel grey -levels to be achievedeither by selecting pre-programmed (rom-based) tables or by down -loading computergenerated tables from the host c.p.u. into anon -board high speed ram. These ram -basedtables can be updated during the fieldblanking interval on a frame -by -framebasis.

Look -up tables can be devised forcontrast -stretching (linear or non-linear),histogram equalization, image negation,clipping, noise magnification etc. and theeffect of these operations can be observed onlive as well as frozen images.

The look -up table is constructed on asingle p.c.b. designed to stack with the restof the frame store boards. Installation isextremely simple, involving ribbon cablejumpering to the other boards without any ,

modifications (other than to add appropriateconnectors).

Two memory sockets are provided, one fora high-speed ram chip (typically 2K x 8,6Ons) and one for a high-speed prom (typi-cally 2K x 8, 6Ons). Both sockets can accom-modate slower ram or eprom chips and150ns devices are adequate for the 256 x256

'Earlier articles in this series appeared in Electronics &Wireless World from November 1986 to March 1987. Acorrection to a drawing in the March issue was given thefollowing month at the foot of page 385.


xel datainput





Translated pixeldata output

`*- 8

Page select =MI5



Address CKcounter

AS -12


tit I,Jontr.:1


t I 3

c.p.0 (control)

8 lines

RIffer OE

Address Ao_7or WR






Bypassbuffer OE

11 8

c.p.u.(write data)

Fig.l. The look -up table allows pixel grey -levels to be manipulated in real time. Look -updata can be in rom, or can be downloaded into ram from the host computer.


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100k 100k

2 11

30 U0



IC 401

74HCT 24 4



_4_ -I%4 All

(I3) 2k2 13 7--4-I a


Outputdata (151





28 27 26






IC 404TMM20180-45 etc

(Ram) Alpor

82S191 etc WR /An(Rom)








3 22




23 (Rom)



27(Ram) 1



IC 403

74 LS 244






14 15

Input 7 IC402 6

data 17 74F 374 16

(11) 4 5

18 19




Pixel b Licontrol -`-'2 C1(2

(I4) -02


3_ 4











All 4k7





12k2WRI> 2C)-





19 1

4 3

15 4


74 LS244

2 5

17 6-o-8 11

11 10

6 9

13 8



D 741_5393

A 1C407





Fig 2 All rnmnnncinte fit nn a einala n r h which ran hp iiimnararl to the. nthar haartie A ennrrn of rnm





to ic tritons, eile

configured frame store which clocks atabout 5.8MHz.

The p.c.b. is configurable for several typesof rom and ram devices in 24/28 -pin and300/600 mil packages.


The look -up table is shown in block diagramform in Fig.!. The board is designed to beinserted between the sample bus and thedigital -to -analogue converter on the analo-gue board as shown in Fig.4 (upper). Bothlive and frozen image pixels are then proces-sed in the same way but the image data in theframe store memory always contains truedata. The colour palette can be located onthe look -up table input bus or on thetranslated pixel output bus.

Two other configurations are also pos-sible:1. The look -up table can be positionedbetween the analogue -to -digital converterand the image memory as shown in Fig.4(lower) and the image data in ram will thenbe translated prior to storage as well asdisplay.2. Both configurations can be implementedsimultaneously using two look -up table

boards to achieve both image write datatranslation and image read data translationat the same time.

The latter configuration cannot usually bejustified for normal applications.


The complete circuit is shown in Fig.2.Incoming eight -bit pixel data is retimed byIC402 which latches the data on the rising

edge of the sample clock: a complete clockcycle is then available for memory accessbecause output data is latched by the d.a.c.and colour palette boards on the next risingedge of CLOCK. This extra delay of one pixelcauses the displayed image to be displaced tothe right. and shifts into view a hidden pixelat the left of the picture while 3Ianking thepixel on the right. This is of no consequencefor displayed images since there are severalperfectly valid hidden pixels. but image




I 1f

Fig.3. Sequence for downloading data to the look -up table's on -board ram.


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manipulation software should be designed totake the displacement into account.

The latched pixel data directly addressesthe on -board rom or ram and the resultantoutput data becomes the new pixel value. Itfollows that 256 grey levels can be translatedinto 256 alternative values depending uponthe contents of the addressed table.

Using 8K x 8 memory devices gives thecapability for up to 32 tables selectable byoptional external switches.

Ram or rom-based tables are selected bythe host control signal ROM/M which whenhigh (or open -circuit) selects the rom or, ifa rom is not fitted, the bypass buffer IC4(0.The bypass mechanism enables the framestore to be operated without the host'shaving to initialize the on -board ram.Various control signals are derived by IC408and IC40,; these are 74HCT series devices asis the host data buffer IC401 for ease ofinterfacing and good noise immunity.

The host gains access by assertingwhich enables the address counter IC4,G.enables buffers IC406, IC401, disables latchIC402, disables buffer IC403 and three -statesthe ram/rom output buffers. The ram isenabled by taking liorwW4 low and data written by pulsing wri low. The address counteris incremented on the rising edge of vTrwhich provides for very fast table updating.

Taking s= -r high enables pixel translationby enabling the latch IC402 and either therom or ram depending upon the controlsignal ROM/12/4 and disabling buffers1C401,406. Link 1 normally selects cr8i; Link 2allows two look -up table boards to beindividually programmed by pulsing theappropriate wR line.

Link 3 will normally be in position 1 for2K x 8 ram devices when pin 23 is n. Link 4allows the use of rom devices when thepolarity of pin 20 changes. Link 5 should bein position 2 when a rom is not fitted; thisenables the bypass buffer IC403 (which canotherwise be omitted).

When the look -up table is positionedbetween the sample bus and the a -to -d onthe analogue board, it must be disabledduring c.p.u. frame memory update; thesignal Er is used for this purpose and isselected by Link 6 in position 2.


The sequence for programming the look -uptable ram is shown in Fig.3. The line istaken low, liomiwN is taken low and data isoutput to IC401; vTii is then pulsed low andthe cycle repeated. Finally, si.r is takenhigh to enable the look -up table.

This example program generates a tablefor negative displayed images:




OUTPUT( WR ) := 0;OUTPUT( WR) :=1;



cpu control /data


Pixel control


Lookup tableboard



d- to -a cony

Memory n Analogueboard t board

o -to -d cory


P,xel contro'


cpu control/datn

Lookup tableboard


Into -a cone

Analogue8 board

8 o -to -d cony

Fig.4. Two contrasting arrangements of the look -up table: above, the frame store memoryalways contains true data; below, image data is translated prior to storage.

Table 1: Link programming All are two way change -overlinks

Link Position 1 Position 2

1 normal2 personality (see text)3 TMM2108 ram4 active low5 rom fitted

6 board location(see text)

6264 ramactive high rom selectauto -bypass in rom-lesssystem


Note when installing the look -up table thatthere is an option for separate data buses forthe d.a.c. and a.d.c. on the analogue board,as shown in Fig.11 of the December 1986article. The links which connect these busestogether should be left open -circuit and anadditional connector installed so that sepa-rate connectors are available for d.a.c. anda.d.c. data. There is provision for this on thep.c.bs available for this project.

The ribbon cable carrying pixel databetween the memory board, colour palette(if fitted) and the converter board shouldnow be connected as follows:





memory--Took-upAn additional jumper cable should beassembled and used to connect

look -up (output).palette--41.a.c.

Finally, the look -up table p.c.b. must beconnected (in parallel with the other boards)to the pixel control bus and the host inter-face buses by clamping additional connec-tors to the appropriate ribbon cables.


Eight -bit picture element data input Eight -bit translated data output 256 entries per table Throughput to 15MHz Up to 32 rom-based tables Up to 32 ram -based tables Auto bypass User -configurable hardware options Simple installation

With the addition of a clock generator, aneight -bit counter to simulate incoming pclsand a d.a.c. at the output this design couldalso be used as a programmable arbitrarywaveform generator with time resolutiondown to 65ns. For a suggested design whichavoids the need to modify the p.c.b. send astamped, self-addressed envelope to theeditorial office. Mark your covering envelope 'Video frame store'.

P.c.bs and components are available fromIpswich Electronics Ltd, Hadleigh Road In-dustrial Estate, Ipswich IP2 OHB, tel. 0473-216056; semiconductor devices from Tech-nomatic Ltd, 17 Burnley Road, LondonNWIO lED, tel. 01-723 1177.


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& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (63)

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68020 cache designOn -chip cache memory increases performance but its sizeis limited. An external cache with 25ns rams takes care of

much larger repetitive loops.

Acache is a high-speed memory local tothe microprocessor that holds themost recently executed instructions

or data. Being closely coupled to the micro-processor, cache memory can be accessedmuch faster than main memory.

Studies of modern programming techni-ques show that programs spend most of theirtime repetitively executing a few tight loopsof code. Cache memory speeds up executionby holding loops just executed so that whenthey are used again they can be accessedmuch faster than if they were held in mainmemory or back-up storage.

With the 68020, small loops of code arecaptured efficiently in the 256byte on -chipcache but performance can be increased stillfurther by adding an external cache to holdlarger repetitive loops.

A fast external cache increases perform-ance particularly when low-cost dynamicram is used for main memory. Access time ofthe dynamic ram is relatively long butrefreshing and propagation delays increaseoverall access time even further.

When an external cache is used, amemory -management unit can be added to a68020 system without performance degrada-tion. With no external cache, adding a pagedmemory -management unit such as theMC68851 for example can cause the intro-duction of an extra clock cycle when acces-sing external physical memory.

Adding a large external cache allows theprocessor to execute considerable amountsof code from the cache without having toaccess main memory. Using fast static ramfor the cache, no wait states are needed soprocessor operation is as fast as possible.

Size of the external cache has a great effecton the hit rate, i.e. the percentage of timethat the processor is executing from thecache as opposed to main memory. FromFig.1 you can see that a considerable hit rate

_ 80

1- 40

.o.ammi-; 2 4

CACHE SIZE (K.bytes)

Fig 1. With a 4Kbyte cache, the processorexecutes from cache memory about 80%of the time.



Access address

Tag, M bits

-- M bi ts


If HIT and VALID ore not both active,data is fetched from memory



Fig.2. Each data item in the cache has an associated tag entry to allow the data to beretrieved. In a fully -associative (content addressable) cache, the tag entry holds a fulladdress and control bits.

Set size=2=number of tag entries per index fieldAccess address



Tag Data V



Inde7:zr bits

1 of 211



Tag 1:fa V

Fig.3. Using low -orderaddress bits as anindex :o a group oftag and data itemsmakes set -associativechaches cheaper.Fewer comparatorsare needed and thereplacementalgorithm can besimpler.


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Access address lm bits)

Tag, t bits

of 2



Index, n bits

Decrease number of comparators-split address into tagand index fields



Data to c p


68000 family architecture

68020 architecture

68020 extra instructions68020 display processing68881/68882 floating-point

coprocessors68851 memory -manage-

ment coprocessor

December 1986pp106 109January 1987pp103-106February pp209-212March pp333.334May pp535 -537

June pp614 616

vo=2-11v3114361-68020 addressand control lines A 15 A14 1A2 lAt lAO


1 of 8K entr



Valid bit


ComparatorCACHE HIT

Update control logic


32 bit data

1 of BK long -worddata entries

BufferenableData bus

(32 bits)


6 8 020









32 bit data




32 bit address bus and control bus -

Cache hit situation I Retry cycle request (cache miss) 2 [Cache update (retry cyc el 3








A15 TA2218 16 14 12 9 7 5 3


2 4 6 B 11 13 15 17A15 A22


Tog address bus

1A27 23 TA19

30 -27 -22


TA30 TA31 TF Co -.2 TS1ZE -1

F 244

A23 430 A31 FC0 -2 SIZEO-1


Logical address bus

Control bus


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Fig.4. Direct -mapped caches, top left, useonly one comparator and replacementalgorithms are unnecessary. A block thesame size as the cache is produced by theindex field so there is only one group.

Fig.5. Cache design for the 68020 using32Kbyte organized in 8Kbyte long words,top right Cache entries are held in

32Kbyte of data ram while tag data withvalid bit is held in tag ram.

Fig.6. When a cache hit occurs, data fromcache ram is placed on the bus but when amiss occurs, halt and bus error signals aresent to the processor to make it retry theprevious cycle. This is to allow time forcache updating.

Fig.7. Using 25ns static rams a very fastcache can be made. The tag field consistsof ram accessed by the address andcontrol bus.








FC20 C




Gtid bit ramtag ram)

A2-14 1101

Fig.8. Simplified cache control logic providingenable,disableandclearfacilities.

can be achieved using a 4Kbyte cache.Increasing the cache size further results inonly small improvement.

In a typical cache, each data item, be it 8,16 or 32 bits, has an entry associated with itcalled a tag field, Fig.2. This tag fieldcontains information that allows the data tobe located.

In most caches the tag field contains alarge proportion of the address bus, thefunction codes and a valid bit indicatingwhether or not a data item has been enteredand is valid. Differentiation between userand supervisor address spaces is provided bythe function -code entry.

There are three basic types of cache - fully

5 16






TA 57'




68 020




Logic address bus

Tag address bus

A31 18

FC 0









Contra) bus TFC0 *TFC2








'C 74F521












17A0 BO -4D






47 CA -9 D"

mc7LF 521



associative, set associative and direct map-ped. Figure 2 shows a fully -associativearchitecture in which the tag field containsthe complete address bug and function -codebits.

Each tag entry has an associated compara-tor. When an access begins, the presentaccess address is compared with each of thetag fields and if a match is detected (a hit), itindicates that the associated data item can beused for the cycle. Because every tag has acomparator, the tags can be compared inparallel which speeds up the process.

By using the whole of the address bus as atag there is no interdependence between thedata items, unlike direct mapping, and sothe hit rate of this type of cache will be veryhigh and related closely to the physical sizeof the cache.

When a miss occurs, i.e. there are no tagmatches, the cache must have some means,1f updating the entry so that it will be validthe next time that that address is accessed.To do this a 'least recently used' algorithmdetermines which entry when overwrittenwill least affect overall performance. Whenthis item is updated, the tag field becomesthe information currently on the address busand the valid bit is set. The next time that theaddress is accessed a hit will occur.

Performance of this type of cache dependson efficiency of the replacement algorithmand relies on the fact that there is nointerdependence betwen entries. On theother hand, fully -associative caches are ex-pensive because of the number of compara-tors required and the complexity of thereplacement algorithm.

Set -associative caches are cheaper. In-stead of holding the whole of the address inthe tag field, the set -associative caches use anumber of low -order address bits as an indexto a block of tag and data items, Fig.3. Thisindex selects a tag from each group andcompares it with the current access address.If one of these entries hits, the associateddata entry is extracted.

The advantage of this type of cache overthe fully -associative type is that the numberof comparators required is only equal to the


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number of groups (or sets) and not thenumber of entries. Size of the index field,and hence the number of entries per group,is thus a trade-off between the number ofcomparators and the cache hit rate. A re-placement algorithm is still necessary forset -associative caches but a simpler round-robin type algorithm can be applied insteadof the least -recently -used one.

In a direct -mapped cache the index fieldproduces a block size that is the same size asthe cache itself so there is only one group,Fig.4. As a result, only one comparator isused and replacement algorithms are un-necessary so this is the easiest type of cacheto implement and the cheapest.

Hit rates of direct -mapped caches are stillquite high (proportional to the number ofentries) but their performance is degradedby address interdependence. This inter-dependence is caused by the fact that theindex field produces an offset into the cachewhich remains the same for addresses whichare modulo with this index, i.e. they have thesame index but a different tag field.

In execution this means that an entry canactually be replaced on the next cycle if thenext access happens to have the same index;there is no way of determining when theentry was last used or how frequently it wasused.


A diFect:mapped cache for data, supervisorand user accesses to and from memory iseasiest to implement. Cache size depends onthe hit rate required and how much you areprepared to spend on fast static rams but istypically 4, 8 or 16Kbyte; in practice,32Kbyte is usually the upper limit.

Since the direct -mapped cache can beused for data accesses it should be designedto avoid stale -data retention. Stale data isdata held in the cache from a previous readcycle; it represents data in memory that hasbeen modified by an external processor writecycle. To prevent stale data, data from theprocessor is written simultaneously to boththe cache and external memory on everywrite cycle. Data read from the cache is thenalways the latest data. This method is calledwrite allocation.

Consider a 32Kbyte cache for the 68020organized in 8K long words (32 -bit words),Fig.5. Cache entries are held in 32Kbyte ofdata ram and tag data with the valid bit isheld in tag ram. The tag field could be 22 bitswide consisting of 17 high -order bits foraddressing an individual entry in the 8Klong -word block of memory, three function -

code bits to distinguish between the types ofmemory access, and two size bits for accom-modating misaligned data transfers (mis-aligned data is 32bit data not resident on a32bit boundary in memory). The valid bit isset each time an entry is made in the cache.

On a cache hit, associated data is readfrom the cache data ram and placed on thebus. Logic i.cs control the data transferdirection to and from the tag and data rams.Address lines Ars-31, function codes Fc0_2 andsize values size.0.1 update the tag field andinformation on the data bus is placed in thedata rams.

Ideally, cache updating should occur

while the read cycle is executing. For thispurpose, if there is a cache miss during aread cycle a signal must be produced earlyenough in the cycle to be fed back to thecontrol logic. This signal places the tag anddata rams in write mode, allowing datapresented on the buses to be routed directlyto the tag and data rams as well as to theprocessor.

This entry -update method is practical forprocessors operating between 8 and 10MHzbut for a 68020 operating at between 20 and25MHz with no wait states, the time avail-able for entry updating may be too small. Analternative method could be to use the 68020late -retry facility during cache misses asfollows.

When a cache miss occurs the cache -

control logic sends halt and bus -error sig-nals to the 68020 simultaneously. Thiscauses the processor' to retry the previouscycle, allowing enough time to enable thetag and data rams for writing. On executionof the retired read cycle, data read frommemory is written into the data rams andinformation on the address and control linesis written into tag ram, Fig.6.


The faster the 68020 becomes, the moredifficult it is to design a system operatingwith no wait states. Therefore to gain anynoticeable performance improvement froman external cache, very fast static memoriesare essential. Fast and ALS logic familiesmake it possible to design a 68020 cacheusing 25ns memories without resorting tocustom or application -specific (asic) devices.

Logic required for the cache divides intofour parts for entry updating, general con-trol, tag -ram operation and data -ram opera-tion. Figure 7 shows tag -ram logic with 16Kby Obit 25ns rams. During a read cycle,addresses presented by the processor areused for indexing into tag ram, output ofwhich is the previously described 22bit tagfield. Provided that certain other conditionsare met, if the 32bit comparator indicatesthat tag ram output matches the currentaddress and control lines the cache -hitsignal arrr is asserted.

Conditions that must be met before ciiican be asserted are the true states of the validbit and cache -enable signal and the untruestates of the i/o enable, cpu-space andram -write signals. These conditions feed thelast comparator stage.

On detecting a cache miss the controllogic causes data presented on Da_31 to beplaced in the tag rams. During the cache hitthe F244 latch outputs are high impedance,thus isolating the address and control busfrom the rams to prevent bus contention.Data -ram logic is similar except that fourF245 bidirectional buffers are used for bothisolating and directing ram data for writing/reading; data direction is controlled by iii

Signals produced by the entry -updatelogic are described in the panel. This logiccan be implemented using simple two -inputgates and D -type bistable devices from fast orALS families.

Control logic can be implemented usingthe same simple i.cs; its complexity dependson the cache facilities required. For exam-

















ENTRY -UPDATE LOGIC SIGNALSCMISS. Active when MAT from the tag comparators isinactive, this signal indicates a cache miss. It should besampled during the middle of the 68020 sj clock cycle.For this the 2. CL K input is used since it is twice that ofprocessor clock CL K.

DSACK(EXT)0.1. These are osxoco signals returnedfrom the external device during a read cycle (R.7 high)when there is a cache miss.

RESET. Connecting the processor reset line into theentry -update logic ensures that the cache operates inits correct mode after reset.

DSACKai. Cache control logic sends these signals tothe processor on assertion of address strobe A so theentry logic assumes a cache hit on each cycle.

HALT, BERR. On detection of a cache miss, cmiss isasserted then these signals are simultaneously sent tothe 68020 to make it perform a retry cycle.

WRITEN. Feeding the ram write -enable pin (w i directly.

this signal allows data to be written during the retriedcycle. It is produced from bsAckirno , and asserted onor close to the tailing edge of s4 of the processor clockDuring s4 the processor latches data.

FORCEN Data ram isolation buffers are enabled bythissignal to allow them to route data during the updatecycle.

INHIBIT. Produced within the update logic, this signalinhibits retry cycle for a cache miss.

pie, consider logic providing cache enable,disable and clear facilities. The valid bit isheld in ram with a clear facility which allowsall cache entries to be cleared.

In its simplest form, the control logiccontains a bistable device which can beaddressed by the supervisor when perform-ing a c.p.u. access to an otherwise unusedc.p.u. function (that is not access levels,breakpoints, interrupt -acknowledge or co-processor space). This access is treated justlike a normal memory cycle. Onec.p.u.cycle causes the bistable device toenable the cache through cAcne_g. Anotherlocation clears entries in the cache by clear-ing the contents of valid -bit ram and a thirdlocation causes the bistable device to dis-able the cache.

Figure 8 is a simplified control -logicdiagram. Signal CACItE_E is used in the com-parator section as vAmoirr; both signalsmust be asserted before a cache hit is con-sidered valid.

When the cache is first enabled or a cacheclear command is issued, the valid -bit ram iscleared. Using the address lines shown,cache clear is initiated by a memory cycle ataddress 107000016, cache enable at address207000016 and cache disable at 407000016.When reading or writing to any of theseaddresses, DSACK0.1 are returned to termin-ate the cycle but data on the bus is irrelevant.

David Bums and David Jones are applica-tions engineers at Motorola's East Kilbrideplant.


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-ThECOMMS TOPICSMonitoring theAtlantic Ocean

IntelsatIntelsat has awarded a contractto Mercury Communications Ltdfor the monitoring of IBS trans-ponder usage on one of its satel-lites.

It will monitor the I1/12G1-1zbeam received in Europe fromthe Atlantic Ocean Intelsat Vsatellite and forward the dataobtained to Intelsat's Washing-ton headquarters. The major ser-vice carried on this satellite is theIntelsat Business Service (IBS)which is a totally integrateddigital service allowing carriersto offer voice, data, facsimile andvideo transmission. Mercury isthe largest user in the world ofIBS and its parent company,Cable and Wireless. is the largestoperator of international com-munications satellite earth sta-tion,- in tlir Intrls,it systcm.

Toshiba to enterUK telecoms

marketAs part of its expansion plans,Toshiba has announced that it isto enter the UK telecommunica-tions market. It will he laun-ching Group 3 (sub 1 -minute)facsimile machines and hopes toreceive approval in the Autumnto sell the first of its small keytelephone systems in the UK.

When announcing his corn-pany's entry into the UK businessfacsimile and key telephone mar-ket. Mr Shunki Yatsunami,chairman of Toshiba Informa-tion Systems (UK) Ltd. forecast aturnover of £100 million($150m) by 1990 for its full rangeof office automation products.

Home bankingnetwork forAustralia

Two UK companies are to supplytheir products to the giant West-pac bank in Australia to enable itto provide its customers with fullhome and office banking facili-ties. Known as Handyline. theservice allows Westpac's custom-ers to transfer funds, pay credit

The Royal National Lifeboat In-stitution (RNLI) is to replace itstraditional call out devices,such as explosive flares, withradiopagers. British TelecomMobile Communications hasdevised a suitable system andis supplying 2000 specially

adapted radiopagers over thenext two years. The first hatchof 1000 is being delivered tolifeboat stations which are, atpresent, hampered by poorcommunications or cumber-some call out procedures.

cards, obtain a statement and thebalances in their accounts usinga digitized voice delivery service.

The complete 132 -port net-work incorporatesVideogate network concentra-tors and Langston's P111 soft-ware. and has been supplied bytheir Australian agents. ThornEMI Information Technology.

World record565Mbit/s opto

linkTelephone Cables Ltd (ICU hasinstalled, on behalf of MercuryCommunications Ltd. what is

claimed to be the longest, oper-ational. unrepeatered. single -mode optical -fibre network inthe world, working at 565Mbit/sand 1300nm using standard pro-duction fibre.

TCL installed the 10 -fibre toprovide a 51km two-way linkfrom Wolverton to Mercury'sWhitehall Satellite Earth Sta-tion, via Bicester in Oxfordshire.Even though it was expected toneed a repeater at its midpoint.attenuation test results sug-gested that this would not benecessary. As Mercury wished tooperate the cable at 565Mbit/s.further tests were carried outwhich provided necessary con-firmation.

Not only has this assisted Mer-cury on this route by avoiding

the need for a repeater site, it isnow possible that most futureroutes can be planned withoutthe need for repeaters, thus re-

and increasing re-liability.

Renaultsby packetswitching

Renault. the French state-ownedcar company, is to extend itsDirect Vehicle Ordering System(DVOS) throughout Europe. Thesystem. developed in Paris by thecompany itself, has been servingthe company's French dealernetwork for the past two years.Now. at a cost in excess of I

million, the 300 Renault dealersin the UK have gone on thesystem which will now also betaken up in Germany. Italy andother European territories.

The total investment by Re-nault in DVOS runs into severalmillion pounds so far. This in-cludes two Amdahl mainframesin Paris and a Tandem computerin London. Major connectionsare made via X.25 packet -switched networks - Transpac inFrance and British Telecom'sPSS in the UK.

In Britain. it represents justthe first phase of extensive com-putet ized communicationsbeing built into the company'sUK operations during the next

two or three years. aimed atputting the Renault network intothe forefront of communicationsadvances being made in the auto-motive industry over the comingdecade.

Small -dishsatellite trials

Trials of a small -dish satellitebusiness communications ser-vice were started by British Tele-com in May. The service willallow users at terminals at manydistant locations in Europe as%veil as the UK to exchange dataeasily and cheaply by satellitewith their company's centralcomputers.

The trial service is based onthe Very Small Aperture Termin-als (VSATs) and uses dish anten-nas of 1.2m (4ft) or 1.8m (6ft)diameter installed on customerpremises. It will enable links tobe set up quickly, even whenterminals are moved to new loca-tions.

It is centred on BT's LondonTeleport, its central satellitecommunications earth station inLondon's dockland, whereequipment from Comsat Tech-nology Products has been instal-led to act as the network hub forthe service. Any remote site maycommunicate with the hub, or toany other VSAT via the hub.

Applications to be evaluatedduring the six months trial in-clude the distribution of newsand images for information ser-vices. internal company electro-nic mail and other interactivecorporate data communications.

First all-optolaser amplifier

repeaterThe first field trial of a laseramplifier repeater has been suc-cessfully carried out in a 120kmfibre link installed in the BritishTelecom network. All optical sys-tems. when developed commer-cially. promise considerable sav-ings in the cost of optical com-munications links. especially forundersea systems. By avoidingthe need to convert the opticalsignal to an electrical one andthen back to light. they will besignificantly cheaper and moresimple to make. and their power


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jttECOMNIS TOPICSrequirements will he reduced.

Still in the experimental stage.it is the optical equivalent of thetravelling -wave tube used as amicrowave amplifier. When heldbelow threshold, it emits an am-plified light pulse at one end inresponse to an incoming triggerpulse at the other.

It has been further demon-strated in the laboratory that.using wavelength -division mul-tiplexing. it can simultaneouslysimplify separate sets of pulses atdifferent light frequencies. It canalso amplify such pulses whenthey are travelling in the devicein opposite directions at once.These lab. tests were carried outover 50km of fibre withwavelengths of 1525 and1506nm and data rates of 280and 565Mbit/s. The light sourceswere distributed feedback laserswhile. at the receiving end of thesystem. channel filtering wasachieved using fixed -wavelengthinterference filters.

The amplifier is a laser. mod-ified by having its end facescoated to reduce their reflectivity500 times, thus destroying thelasing action. A steady voltage issuperimposed between the upperand lower surfaces to establishan electric field across the cavity.As a result, when a pulse of lightenters the cavity at one end, itstimulates the production of ex-tra photons which leave the cav-ity at the far end.

Expansion insecond phone

serviceResidential customers and smallbusinesses in the Nottinghamand Derby areas will take part intest marketing of the new Mer-cury 2300 telephone service. Inaddition, the company has ex-tended its local call services forits directly connected customersin the Birmingham and Man-chester areas.

The two Midlands cities arekey locations in the Mercury"Figure of Eight" network, andhave been selected to gauge theimpact of the service with re-sidential and smaller businesses.It will offer cost savings averag-ing 15 per cent on long-distancecalls, and up to 10 per cent onselected international routes in-cluding USA. Canada, HongKong and Bermuda. Mercury

will monitor the trial closely.carefully evaluating customerreaction and the degree of take-up as part of its plans for anationwide service to completewith British Telecom.

To use the new service, cus-tomers will need to purchase aspecial Mercury Telephone at acost of £51.99 (inc. vat) and payan annual fee of £8.62 (again inc.vat) for an Authorisation Code.Calls are made using the custom-er's existing exchange line sothat, to place a Mercury con-nected call, the trunk or interna-tional call is dialled in the usualmanner except that, prior tocommencing dialling, the M(Mercury) button on the phonemust be pressed.

The local call service, whichwill be most beneficial to thosecompanies with more than 30exchange lines, was previouslyonly available to directly con-nected customers in London. Itwill enable business customersto make savings of up to 30 percent on local calls.

Fax expansionfor BritishTelecom

With facsimile growing at anaverage of 100 per cent each yearfor the past six years and fore-casts suggest that next year afurther 75,000 terminals will beadded to the 90,000 currently inoperation. British Telecom hasadded two new machines to itsrange. They are a personal com-puter based machine providingstore and forward features for

fax, linked with test processingfor the high volume user andcompact, low-cost, desk -topmachine incorporating an integ-ral feature phone. The former,the MerlinFax PC100 providesthe user with an icon -basedmenu display for ease of opera-tion. At each stage, help informa-tion is available on request toguide the inexperienced user.

The latter, the HS20, is a jointproduct of British Telecom andTeleverket, the Swedish PTT,and has already been launchedon the Swedish market. Lookingrather like a sophisticated fea-ture phone it is claimed to in-corporate sufficient features tosat isfc mast users.

Prudentialapproach to


Prudential Corporation, the in-surance and financial servicesgroup. has taken delivery of theone -millionth line of Plessey'sISDX digital p.a.b.xs as part ofthe process of implementing oneof the country's largest and mostsophisticated private digital net-works. Based on ISDXs of varioussizes it will extend from Scotlandto the West Country.

To date, the number of exten-sions at Prudential's five Londonand Reading head office estab-lishments and another selectednine offices around the countryis 4.250 in the network featuringthe latest d.p.n.s.s. (digital pri-vate network signalling system)

technology. This allows manyfeatures such as call diversionand call-back when free to beavailable between offices. Inaddition. Direct Dialling In(DDI I routes an incoming calldirectly to the called internalextension. At the present time.the company's 24 regional officesare being equipped with smallerISDX-SN exchanges on a stand-alone basis. In due course, whenthis replacement programme iscompleted. they will he con-nected to create one of thelargest and most sophisticatedprivate digital telephone net-works.

Since being launched as theIDX (Integrated Digital Ex-change). and now offered withISDN features. Plessey has soldover 3.000 of these switchesworldwide and achieved a salesrevenue of around £250 million.

Packetswitching cutsbank security

costsLargest clearing bank. NationalWestminster. is to use its privateX.25 packet data communica-tions network to carry alarm datafrom branches all over the UK.This will enable it to dispensewith the central alarm monitor-ing stations of security companyChubb Alarms Ltd. Chuhh is re-sponsible for the security of 350out of the banks 2000 branches.

Chubb engineers and NatWestd.p. experts worked together onthe system developed by Chubband already in use by two otherEuropean banks.

Under the programme. bankbranches are being equippedwith a specially developed inter-face unit which accepts signalsfrom intruder alarm systems andthe electronic security devicesprotecting Automatic TellerMachines (ATMs). When regular-ly polled by one of the sevencentral monitoring stationsaround the UK. an interface in-serts encrypted data packets intothe private network. Chubbclaims to have reduced thenecessary data traffic by 90 percent without sacrificing the levelof security.

Telecomms Topics is written byAdrian Morant.


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RESEARCH NOTESIntensive carebiofeedback

What is probably the most soph-isticated biofeedback systemever invented has been developedby John Packer of the Depart-ment of Electrical and ElectronicEngineering at the University ofMelbourne. It's an automatic.computer -based device for stabi-lizing the blood pressure ofseriously ill patients. This is nor-mally achieved manually by reg-ulating the infusion of differentdrugs, a task that involves takingblood pressure readings usuallyevery 30 seconds.

An obvious electric alternativewould be to have a continuousblood -pressure sensor and con-nect it to a dispenser for twodrugs, one to increase bloodpressure and one to lower it. Thiswould in theory eliminate anyneed for manual intervention bynurses. It isn't as simple as that.however.

Mr Packer says that there areseveral reasons why researchersin Britain, the USA and Australiahave found difficulty in im-plementing such a biofeedbacksystem for blood pressure con-trol. One is noise from the bloodpressure transducer caused bymovement or by coughing:another is the variation inpatients' response to a drug atdifferent blood pressure levels.

These problems have nowbeen taken care of by the de-velopment of a computer prog-ram that can distinguish signifi-cant changes and convert theminto an appropriate response.The system adapts to variationsin patient sensitivity andincorporates a wide range of safe-ty alarms. Patient data is display-ed graphically on a v.d.u. andstored on disc for subsequentanalysis by medical staff. Doctorsand nurses can interact with theprogram through a standardkeyboard.

Clinical trials involving morethan 80 patients have been suc-cessfully carried out in intensivecare and cardiac surgical units.

How the brainis wired

Speculation about how the hu-man brain works has been apreoccupation since time im-

memorial and never more sosince the advent of the compu-ter. But whilst nerve cells orneurons behave in some wayslike silicon switching elements.the similarities are in other waysquite limited. The switching rateof a neuron is, for example.thousands of times less than thatof a typical c-mos gate. Neuronalarchitecture is also markedlydifferent from that pioneered byvon Neumann, being massivelyparallel. But of course, it isn'tquite as simple as that or wewould already be well on the wayto suitcase -sized computers withhuman intelligence and con-suming only a few tens of watts ofpower.

One of the most puzzlingaspects of the brain is how itwires itself up in the first placeduring foetal development.Obviously hidden away in thegenes there must be a sort ofwiring diagram written inmolecular code. But it can't bejust like a computer circuit dia-gram because there simply isn'tenough space on the genes for allthe data. This has led molecularresearchers to speculate that thebrain must in some way 'selfwire' itself.

Dr Adrian Aitken of the Uni-versity of New South Wales hasnow provided a little more evi-dence that this is exactly whatdoes happen. His first achieve-ment was to make a preparationof an intact foetal rat brain with-out disturbing the structure.Hitherto brain researchers haverelied on making microscopeslides from thin slices of tissue.In computer terms. Dr Aitkenhas discovered how to take thelid off whilst others are attackingthe innards with a chain saw.

Having got inside the foetalbrain, the next step was to followthe growth of the neuronal ax-ons, the links or wires by whichneurons connect themselvesinto the circuit matrix. The pre-cise method employed was de-tailed and complex but it led DrAitken to some fascinating andsignificant conclusions.

Neurons, it seems, have mole-cules that cause the growingaxons to follow a sticky trail inthe brain tissue. It's as if the pinof an i.c. were to sniff outanother i.c. and begin growing awire link. Dr Aitken says that the'stickiness' of the top of a grow-ing nerve fibre governs the direc-tion in which it \ill grow. In this

way the nerves do not necessarilyhave to 'know' which other cellsof the developing brain to con-nect to. All they have to do isfollow the adhesive trail.

These findings, recently pre-sented in a paper to the Austra-lian and New Zealand Society forCell Biology are significanttheoretically and also clinically.In future research. Dr Aitkenintends to examine more closelythe mechanism of nerve -fibreguidance and he hopes that, withadditional information. it may bepossible to direct the growth ofnerve fibres and ultimately de-termine their networkarchitecture. This has applica-tion in the treatment of severalnerves and also in the under-standing of degenerative neuro-logical conditions such as multi-ple sclerosis and Parkinson's Dis-ease. Conceivably it might alsofacilitate brain transplants!


Implanting dopants directly intoa silicon substrate is an attractiveproposition for the manufactureof v.I.s.i microcircuits. Apartfrom avoiding the need for amask such a technique wouldpermit variations, either in thelocation or degree of doping.

A research programme involv-ing Manchester University. theUniversity of Manchester Insti-tute of Science and Technology(UMIST) and IBT-Dubilier is cur-rently looking at practical waysof implementing the Cu. ham-Dubilier liquid metal ion source,

Dopant ions

I Accelerator

Liquid metal(reservoir


shown in the diagram. The ionsource consists of a positively -charged needle of less than10p.m diameter placed near anion accelerator electrode. Liquiddopant is fed by capillary actionfrom a reservoir behind theneedle and is then emitted as abeam. Focussing is achieved byelectrostatic or electromagneticlenses.

For the system to work prop-erly, the dopant material mustmeet certain tight constraints. Itmust flow over the needle with-out dissolving it. It must alsohave a suitable low vapour press-ure. Unfortunately neither arse-nic nor boron, the most commondopants. meet these criteria.

What the group have found isthat certain alloys of the dopantsdo meet the criteria and thatonce the alloy has been ionized,the unwanted component can beseparated by a technique analo-gous to mass spectroscopy. (Re-member the ion traps on oldcathode ray tubes?)

Where arsenic is concerned.an alloying material that workswell is platinum together with atungsten needle. With boron,platinum is also employedthough rhenium is the preferredneedle material. Computer stu-dies are now going on at Man-chester University to try and findthree -component alloys that per-form even better.

Flying powerstation

A new slant on power generationis a flying windmill being de-veloped by Associate ProfessorBryan Roberts at the Universityof Sydney. The Gyromill, as it'scalled, is a cross between a wind-mill and an autogyro and fliestethered by steel cables to theground. These cables not onlyprovide anchorage but also con-tain power cables and controlcircuits for ground commandsignals.

If the whole idea of putting apower station in the sky seems alittle eccentric. ProfessorRoberts explains that there aretwo major advantages from thisapproach compared to the use ofground based windmills. Con-ventional windmills of the sortnow springing up around theshores of Britain are so close tothe ground that the wind is bothslower moving and more turbu-lent than higher in the atmos-phere. Since the extractablepower is related to the cube ofthe windspeed. the advantages ofa few extra mile/h are obvious.Turbulence is a different andaltogether more serious problemand has led to at least one wind-mill in the USA breaking upcompletely. If you doubt the im-


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RESEARCH NOTESpact of turbulence on largestructures near the ground, justrecall how bumpy it gets as anaircraft is landing.

The Gyromill prototype hastwo contra -rotating blades, each4 metres in diameter and eachdriving a 3kW generator. Profes-sor Roberts has already done thesums to show that this can easilybe scaled up to several mega-watts at least. Tests on the pro-totype have also shown thatthere are no serious problems.

When the windspeed exceedsabout 25km/h, the Cyromill willtake off from the ground andhover like a kite, generating elec-tricity as it does so. If the wind -

speed near the ground isn't quitestrong enough for an unassistedtake -off, then the generators canhe employed in reverse as motorsuntil the Cyromill is airborne.The motors then revert to theirnormal role as generators.

The mechanics of the machineare extremely complex, to ensurethat it will fly stably in all windconditions up to gale force. If thewind does become dangerouslygusty, then the Cyromill canadjust its blades so as to landsafely and switch off. ProfessorRoberts hopes eventually tobuild a fully automatic versionthat will take off and land underfull computer control. The com-puter would respond not only tothe prevailing wind conditionsbut also to the needs of theelectricity utility. Gyromillscould be kept on the ground andthen launched automatically atperiods of peak demand.

At the moment, flying power -stations on this grand scale maybe a little way off, even in Austra-lia. But Professor Roberts be-lieves that the idea may haveimmediate applications in areaslike Antarctica where the prob-lem of ground turbulence is ex-acerbated by icing and wherediesel generators pose difficul-ties of their own. Flying at about300 metres above the icy waters,a Cyromill would be fed by asteady stream of air, largely freefrom drifting snow.

Major researchgrants forantennas

Over the past few years theAntennas Group in the Electro-nic Laboratory at the Universityof Kent has been awarded sub-stantial research grants from theScience and Engineering Re-search Council and BritishAerospace for work on satelliteantenna systems. Recently thegroup has received two furthergrants, from the SERC and theRoyal Signals and Radar Estab-lishment, each of more than1100,000. The work of thegroup, surpervised by Dr TedParker, Reader in Radio Com-munications, and Dr R.J. Lang-ley, Lecturer in Electronic En-gineering, is concerned with stu-dies of frequency -selective sur-faces.

These can be used to constructcomponent parts ('subreflec-tors') of communications anten-nas. which can then becomecapable of operating on severalwavebands simultaneously,thereby improving the efficiencyand cost effectiveness of the sys-tem. In some of these applica-tions, the surfaces have to bequite tightly curved, and theaims of the project funded byRSRE are to improve the designprocedures for curved surfacesand to develop manufacturingtechniques.

In other applications, two ormore surfaces are stackedtogether in cascade, or the sub -reflectors have partly metallicand partly frequency selectivesurfaces. The grant from SERC issupporting a study of these morecomplex structures.

Electrolumine-scent blues

A paper published jointly by ateam of applied physicists atDurham University and a groupof chemists from UMIST de-scribes what they claim is thefirst ever room -temperature blueluminescent device based onmetal -insulator -semiconductor(m-i-s) technology. This offersan alternative configuration tothe more common p -n junctionused in opto-electronic devices.

The latest m-i-s diode employs


Silicon phthalocyanine




zinc selenide (ZnSe) as a 11 -VIsemiconductor. This is on a gal-lium arsenide substrate fabrica-tion using metal organic che-mical vapour deposition(m.o.c.v.d.) at room tempera-ture.

The 'insulator' part of the m -i-s structure is a Langmuir-Blodgett (molecular thickness)film made of a silicon phthalocy-anine compound. At an appliedvoltage of around 2V, a current ofapproximately lmA flows; this isthought to be limited by theinternal resistance of the siliconphthalocyanine layer. Undersuch conditions the researchersreport a blue -white emissionfrom beneath the gold contactlayer. Such light is said to beclearly visible under normal in-door lumination.

Further research is now inprogress to establish the opti-mum thickness of the 'insulator'layer.

Magnetohydro-dynamics to

beat pollutionA research team at the Universityof Sydney has developed a prac-tical means of improving theefficiency of existing coal-firedpower stations, using a novelmagnetohydrodynamic conver-ter. Magnetohydrodynamics isthe process whereby hot gasesfrom the burning fuel can heused to generate electricitydirectly.

In essence, the m.h.d. gener-ator works by taking the hotgases and ionizing them with aseed material to make them elec-trically conducting. The gasesthen pass through a magneticfield in which charge separationoccurs, resulting in a currentflow between pairs of collectorplates and an external circuit.

The Sydney m.h.d. generatordiffers from the usual approachof feeding the gases along astraight channel; instead it em-

ploys a disc structure in whichthe flow is radial. This makes thesystem more compact and en-ables it to produce much morepower per unit volume thanlinear designs. It is also substan-tially cheaper because the mag-net used is simpler in design.Where the researchers, led by DrSteve Simpson, have made sub-stantial advances is in the de-velopment of insulating mate-rials capable of withstandingtemperatures of around 2000°C.

The disc m.h.d. generator, oneof only three of its kind in theworld, has now been runningsuccessfully for almost a year atWhite Bay power station in NewSouth Wales. Tests show that it isperforming beyond expectations.The team is particularly pleasedwith the generator because theyclaim that the other two discm.h.d. generators at StanfordUniversity in the USA have notproduced such encouraging re-sults. Also encouraging are theresults of a computer studywhich predicts that it should bepossible to scale the design up.

Although m.h.d. is still in itsinfancy in terms of development.many countries are now lookingat the technology as a means ofreducing pollution and gettingmore electricity from a givenamount of fuel.

Electricity is generated


CoalcombustorExhaust power plant

I Steam

Where m.h.d. scores is that itmakes use of very high tempera-tures at which conversion effi-ciency is high. And because theexhaust gases are still extremelyhot by normal standards they canbe re -used to boil up water anddrive a turbine in the conven-tional way. The most practicalway of employing an m.h.d.machine is therefore as a sort of'front end' to an existing station.But whether extensive use ofm.h.d. would improve efficiencyto the point where coal-firedpower stations are as competitiveand free from acid rain as nuclearstations remains to he seen.

\otsv tie\6

Disc channel

Research Notes is written byJohn Wilson.


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Minimal epromprogrammer

Special protocols devised to suit last month's hardwareallow software to take over all the tasks in reading or

writing eproms.

The simple hardware described in theJune article can be controlled by anycomputer with a serial interface cap-

able of communicating at 9600 baud. Creat-ing the necessary software is not an enor-mous task, but is made vastly easier by thehelp of a high-level language such as Basic,Pascal, or C. Most of the procedures neededare available from such languages, with theexception of a few low-level functions whichmay require either machine code or systemcalls depending on the operating system inuse. I have used the C language to imple-ment the procedures for two different com-puters and three different operating systemsand found the source code was portable in allcases with only the need for a few differentassembly language routines to be bound inat link time.

Features of the program break down intothree classes: the necessary, the fairly essen-tially useful, and the nice. Necessary are thefeatures required to write and read epromsfrom and to disc files. The useful features addthe capacity to display eprom contents, toverify eprom contents against files and todisplay informative screens and warningmessages. The nice features may includeprovision of progress reports during pro-gramming, verifying and copying, dif-ferentiation during verification between re -programmable and erasure -requiring faults.and file name and file size buffers to elimin-ate the need to retype the file identification ifmultiple copying and/or verification is re-quired.

The necessary features are built from thefollowing software functions:1. initialize serial communication to 9600baud, no parity, two stop bits. eight data bits:2. open a disc file for reading or writing, andclose it again:3. flush the computer's and/or uart's serialreceive buffer:4. output an eight -bit character through theerial port with no handshake:

5. wait for an eight -bit character to arrivethrough the serial port, input it, with nohandshake:6. do nothing for 50 milliseconds (± 5ms).

Some of these functions may not requireprogramming: for example, on my CP/Mmachine dip switches set up the serial portparameters. Some functions may come aspart of your language, and some may requiremachine code or assembly language pro-gramming.


Table 1. Hardware settings for different communica-tion parameters (uart type 6402, 8017 8502 etc.)

Pin High Low

35 No parity Parity enabled36 Two stop bits One stop bit39 Even parity Odd parity

A detailed discussion of these functionswill follow, but first let us assume they areprovided, and consider the program fromthe top down. The two essential functions ofthe eprom maker are transfer of rom con-tents to and from disc files. These use thefollowing program flows.

For reading: initialize. flush the buffer,open a disc file to read into, then repeat thefollowing as many times as there are bytes tobe read:

send a dummy byte (say. 0).input a byte and store it as next in the

file,send another clib Imy byte,input a byte and discard it.

After all bytes are read close the input file.For writing: initialize, flush the buffer,

open a disc file to write from, then repeat thefollowing as many times as there are bytes towrite:

fetch the first/next byte from the fileand output it,

unless the fetched byte is FF1h. delay50ms

input a byte and discard it,output the fetched byte again.input a byte and discard it.

Finally inform the user writing is done andclose the output file.


If serial communication parameters are notavailable as listed above you may use differ-ent parameters and change the hardware inaccordance with Table 1, perhaps with moredividers after the 4520 in the bit -rate gener-ator.

Opening and closing disc files are tune -


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tions of any high-level language, and withmost you can use buffered file i/o to saveconsiderable execution time.

If a serial communication flush functionis not provided it can be implemented by asoftware loop that repeats as long as there isa byte to be read from the serial port -reading in a byte, discarding it, and tryingagain.

Outputting and inputting with no hand-shake may require an interface directly tothe hardware of your uart, as operatingsystem calls (for example under MS-DOS)may scan Dm or other signals before sendingor receiving serial bytes. The (not recom-mended) alternative to taking the troublewith software is to wire up a special DB25serial plug involving pins 4,5,6 and/or 20 andperhaps others with the right combinationof shorting links.

On a simple computer, like my CP/Mmachine, the delay procedure is im-plemented by simply entering a loop tocount up to a constant number, uselessly.This is not practical with IBM p.c.-typemachines for several reasons. One is thatprocessor speeds vary greatly. Somemachines use two or even three differentprocessor speeds selectable by the user, andsome turbos don't even have the standard4.77MHz as one of their options. Added tothis is the difficulty that the various mem-bers of the Intel and NEC families of proces-sor used in p.c.s queue instruction in aninternal pipeline in differing ways, so thatthe time required to run a delay loop is notproportional to processor speed from onemachine to another. Finally, a p.c. runningDOS is not strictly a single thread machine,for the foreground task is stopped at inter-vals to allow d -ram refresh and for a systemclock interrupt which may be trapped bymemory -resident software.

The solution to these problems is to let thesoftware figure out the delay parameters foritself. As in the simple case, a delay loopcounter is used, but the counter goes up to avariable limit rather than a constant one,and the variable is adjusted each time theprogram is entered.

The assembler and C functions given inTable 2 show how this can be done. Thedelay(n) function is tested 50 times by theadjust( ) function using an initial value for nwhich is about right to produce a 50ms delayon an XT using a 4.77MHz clock. DOSsystem calls 2Ch and 2Dh to set and read thetime are bound in using assembler routineszerosec( 1 and readsec( 1. These allow thenumber of seconds elapsed during the 50in -line iterations of delay(n) to be measured.The resolution of these system calls isworse than 50ms, but repetition of the delaymeans the timing of each delay call ismeasured to about ± lms, five times asaccurate as is required for eprom program-ming.

Table 2 shows how time informationobtained from readsec( ) can be re -formattedto an integer from the mixed binary anddecimal format supplied by DOS (the highbyte of the data word is seconds, the low byteis hundredths of seconds), then cast into afloating point form, and then divided intothe expected number of 2.5 seconds to

Table 2. Two C and two assembler functions to adjust the delay function del(newfac) to 50ms Functionszerosec and readsec should be declared -public. assembled and then linked to the C program.

delay( timer)int timer;

int n;for ( n=1; n< = timer ; n++) ;


int timer,readsec(),factor,timfac,newfac;float correct,timff;factor=2200;

zerosec(); /*zeroes seconds, leaves minutes

delay (factor);delay (factor);delay (factor);

and etc to fifty times

timer= readsec();/*returns sec in hi byte, hundreths

timfac=(100*(timer/256) + (timer&Oxff));/*corrects this to an integer*/

timff=timfac;/*casts this to a float*/

correct = (250/timff);newfac = (correct * 2200.0);

printf ("The speed factorreturn (newfac);

rosec : pushpushpushmovintmovmovintpopspoppopret

bpdxcxah,2ch21h ;read timedx,0 ;zero secsah,2dh21h ;set timecx -


& hours*/

in lo byte*/

of your PC is %f.\n",correct);

readsec_: push bppush dxpush cxmov ah,2chint 21hmov ax,dxpop cxpop dxpop bpret

obtain a correction factor for the originalguess at the delay constant. A correctedconstant is then returned to the calling mainprogam for use in the 50ms delay loop whenrequired. The entire process takes 2.5seconds at most, and (for the sake of simpli-city) resets the seconds counter of thesystem clock once to cause a 'loss' of at most59 seconds.

Now we turn to useful aspects of thesoftware. Menu screens can be designed tocontrol of the various modes of operation. Itis also useful to add a mode to display thecontents of an eprom while they are beingcopied to a disc file.

A verify function is very helpful. It readssequential bytes from the eprom but opens afile for reading rather than writing, andcompares the eprom contents with sequen-tial bytes from the file and displays anydifferences found.

The first of the nice functions memorizesthe identity and size of the last file used toallow the re -use of the same data. Thisfeature has certainly saved me enough in'time and temper (and typing errors) to havemade the tussle with string processing in itsimplementation worthwhile.

Another function puts blobs on the screenin blocks indicating 1Kbyte processed, togive a progress report. One blob per 64 bytesgives just enough information during pro-gramming to give comfort that something ishappening without wasting too much timedoing screen writes. It is also useful that the

number of bytes to be programmed can beselected to be less than the full epromlength, allowing partial programming wherethis is suitable. To program the popular 2764eprom fully takes eight minutes (less if thereare 'blank' areas with FFs in them). A 27256can take half an hour to program.

A final nice feature is an addition to theverify function that reports whether epromerasure is required when there is a mismatchbetween a file and the eprom contents.Erasure is required when an eprom bit is lowthat should be high. The software reportseach such mismatch with a message and anaudible signal. This makes checking thesuitability of an eprom for overwritingwith agiven file a matter of listening rather thancareful watching. Silence during the verifyfunction means overwriting is possible be-cause all mismatched bits are high.

The author can supply executable soft-ware, a brief manual on disc, and a programuseful for comparing two binary files. Thebasic version is available for a Morrow MD2or MD3 CP/M system, or a Morrow with SWPcoprocessor under CP/M86 or PC -DOS for£10 plus s.a.e. disc mailer froth B.J. Sokol,47 Grafton Road, London NW5 3DX. Thefully featured program as described here isavailable for PC compatibles with a COM1:serial port for £15 plus mailer.Jerry Sokol started his design consultancyin the U.S. in the early 1960s. He alsolectures in renaissance literature at LondonUniversity.


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MACA new way of getting more tele-vision signals through a givensatellite transponder bandwidthfor tv signal distribution or d.b.s.has won an international prizefor a British researcher. CalledD-SMAC, the system is the workof W.H. Dobbie of British Tele-com Research Laboratories,Martlesham Heath, Suffolk. MrDobbie has won the $10,000Piero Fanti international prizefor 1986 given by the Italiancompany Societa TelespazioS.p.A. It honours the late DrPiero Fanti, who was Telespa-zio's first director general, and isawarded to the winner of a com-petition open to all students andresearchers in countries whichare members of INTELSAT. Theprize was presented at a

Washington, DC meeting of IN-TELSAT signatories in April thisyear.

The new D-SMAC systemallows four tv signals to be car-ried by a 36MHz transponderchannel, compared with the cur-rent maximum of two signalsusing the PAL standard. It is

based on the existing D2 -MACsystem which has already beenproposed for d.b.s. and cable tv inEurope. In the name D-SMAC,the 'D' indicates that data is

multiplexed with the video signalat baseband, the 'MAC' is theaccepted abbreviation for multi-plexed analogue components,while the 'S' means that theseanalogue components are sub -sampled.

Basically the four tv signalsare transmitted through a36MHz transponder by frequen-cy division multiplex (f.d.m.) -that is, one tv signal in 9MHz.The techniques used to achievegood bandwidth efficiency in-clude a non-linear pre- and post -filtering process, the sub -sampling mentioned above (cal-led modified quincunx sub -sampling) and a method of adap-tive interpolation which allowsfor practical analogue transmis-sion. The system uses samples inthe current tv field for interpola-tion and so avoids an immediaterequirement for frame delay/stores and motion information.

Apart from signal distribution,Mr Dobbie's prizewinning paperstates that the same techniquecould be used in d.b.s. to allow a

This antenna at British Telecom International's Goonhilly earth station,Cornwall, is to be used for the BTI Skyphone service -a satcom schemeallowing air travellers to make in-flight telephone calls from aeroplanes.The scheme follows from INMARSAT's 1985 decision to offer aeronautic-al mobile satcom services through its L -band maritime satellite network(January issue, p. 32). BTI Skyphone is one commercial system set up toexploit this new form of public telecommunications and will operateinitially on transatlantic routes through INMARSAT's Atlantic Oceansatellite (MARECS B2) at 26° W. International direct dialling will bepossible for passengers. Voice signals will be digitally encoded, initially at9.6kbit/s, and data transmission will be available through the system,initially at 600bit/s. Standard airborne equipment will have up to fourtelephone channels per aircraft (four simultaneous calls). Avionicsmanufacturers are at the moment considering wall -mounting cordlessunits and integral seat -back units. Eventually the BTI Skyphone servicecould be extended to work through the INMARSAT comsats over theIndian and Pacific Oceans.

doubling of broadcasting capac-ity "without significant loss ofquality compared with PAL inthe short term, with the optionof trading the increased capacityin a compatible manner for en-hanced definition and aspectratio in the future." The sub -sampling method "allows the en-hancement information to beoverlaid in an effective and sim-ple manner."

Mr Dobbie works in a groupconcerned with terrestrial inter-faces and baseband processingwithin the Radio and SatelliteCommunications Division atMartlesham. This outfit is nowbuilding a prototype codec basedon the D-SMAC principle. It willbe used for signal distributiontrials over a typical satellite linkprobably later this year, to in-clude subjective comparisonswith current distribution sys-tems.



Digital television, high -definition tv, telecommunica-tions to aircraft. adaptive chan-nel coding, correlative phasemodulation, simulated on -boardprocessing and countermeasuresagainst fading are among themany advanced radiocommu-nication experiments booked forthe ESA Olympus satellite after itis launched next year.

This large multi -purpose com-sat, weighing about 1.5 tonnesand measuring 26 metres fromtip to tip of its solar arrays, isreally an orbiting test-bed foranything that the EuropeanSpace Agency and other orga-

nizations may want to try out forthe future. In geostationary orbitat 19° W, the first flight modelwill carry four distinct payloads.One is for direct broadcastingprojects, another is for special-ized services (such as education,newsgathering, business), athird is for advanced com-munications experiments at 30/20GHz, while the fourth is forpropagation studies.

At a recent lEE colloquium on'Satellite communications above18GHz' an overall picture of theexpected utilization of thesepayloads was given by C.D.Hughes of ESA, Noordwijk,Netherlands. Probably of mostinterest to E&WW readers is theintended advanced communica-tions work at 30/20GHz - whichof course is on the verge of themillimetre -wave region. Thepayload for this comprises three30W t.w.t. transmitters and twoindependently steerable spotbeams with a beamwidth (to the3dB contours) of 1°. The e.i.r.p.at beam centre is about 54dBW,allowing the use of small dia-meter antennas for earth sta-tions.

Altogether this payload pro-vides one wideband channel of700MHz bandwidth and twonarrow -bank channels of 40MHzeach. Uplinks are at 30GHz anddownlinks at 20GHz.

ESA will use this payload fordata relay experiments. Thesewill be to and from the Eurecaorbiting scientific platform dueto be launched in 1989. Thislow -orbit vehicle will carry aninter -orbit communicationsmodule which will send and re-ceive signals to and from thegeostationary Olympus trans-ponders. Eureca will be trackedby the steerable antennas ofOlympus and the data originat-ing from the platform will betransmitted and received by anESA earth station in Europe.

In broadcasting, said Hughes,there is a plan to demonstratethe ability of Olympus to relayhigh -quality television picturesand sound from remote parts ofthe world to European locationsfor broadcasting. In particular.using the steerable spot beamsand ESA's air transportable earthstations, it will be possible torelay items of topical interestfrom, say, South America to astation in Europe, from wherethe Olympus d.b.s. payload canhe employed to distribute the


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SATELLITE SYSTEMSprogrammes. The EuropeanBroadcasting Union has showninterest in doing high -definitiontv experiments using the 30/20GHz payload.

The wideband capability ofthis payload will be used to makemeasurements of phase correla-tion in very wide band transmis-sions at millimetre -wave fre-quencies. There will also be anumber of scientific experimentsconcerned with countermea-sures for fading. These will in-clude experiments with diversi-ty, both in frequency and space,and with digital techniques foralleviating the effects of fading.Most of the more general experi-ments, for example a BritishAerospace video conferencingproject, will investigate fadecountermeasures as a necessarypart of radiocommunications at30/20GHz.

Many of the planned experi-ments are in the field of businesscommunications using smallearth stations, continuedHughes. The Canadian Com-munications Research Centrewill set up an experimental net-work of stations for such busi-ness communications. It willalso investigate the potential ofon -board processing systems.using double -hop techniquesand equipment on the ground tosimulate a future satellite signalprocessor.

British Aerospace and the ESAare to run a business com-munications experiment in theUK involving data, voice andvideo conferencing. Initially theESA's TDS-6 earth stations willbe used for this experiment atthree UK locations. Telespazio,in collaboration with thePolitecnico di Milano and otherItalian organizations, have alsosaid they want to carry out busi-ness communications and tele-conferencing experiments.

In data transmission, a num-ber of European scientific orga-nizations including the Universi-ty of Graz (Austria), RutherfordAppleton Laboratory (UK) andCNUCE (Italy) will operate aninter -networking experiment.This will link together computernetworks in the various coun-tries to demonstrate the possibi-lities of high-speed operation ofsuch systems. A further experi-ment called CODE (CooperativeOlympus Data Experiment) hasbeen devised by an earth stationworking group consisting of rep-

resentatives from universitiesand sceintific establishments.This will involve linking togetherscientific and educational estab-lishments using very small aper-ture terminals (February issue,p. 160, on v.s.a.ts) throughoutEurope.

Also using near mm -wave fre-quencies is the Olympus payloadfor propagation studies men-tioned above. The general ideahere is that the satellite providesa platform for source of electro-magnetic radiation in space.These are in the form of beacontransmitters. Olympus carriesthree such transmitters, withfrequencies of 12, 20 and 30GHz.They are all linearly polarizedand accurately aligned with eachother in polarization.

The 20GHz beacon can beswitched by telecommand be-tween two orthogonal polariza-tions or made to switch automa-ticaly between polarizations at arate of about 1kHz. This featureallows accurate measurementsto be made of differential polar-ization. The 12GHz beacon has aglobal converage with a mini-mum e.i.r.p. within coverage of10 dBW. The 20 and 30GHzbeacons have European cover-age, each with a minimume.i.r.p. of 24dBW. They aremutually coherent, being de-rived from a single oscillatorsource within the satellite whichis duplicated to ensure long-term reliability.

These beacon transmissions,said Mr Hughes, not only allowabsolute measurements of atte-nuation and cross -polar effects at20 and 30GHz but also permitdirect comparison simul-taneously between 12-, 20- and30GHz phenomena. He felt thisto be very valuable because it willenable the considerable amountsof propagation data already col-lected at 12GHz to be scaled tothe higher frequencies.

Offshore multi-channelsatcoms

Winds in the North Sea oftenreach speeds of over 100 knots(185km/h), so the dishes of anysatellite earth terminals usedthere have to withstand heftywind loadings which can deflecttheir radiation beams away from

the satellite position. In a newoffshore terminal, claimed to bethe first multi -channel satellitesystem used in the UK section ofthe North Sea oilfields, this prob-lem is dealt with by sophisticatedposition -control servos whichrespond to the wind buffetings.

The new satcom terminal,built by Ferranti, is installed in afloating production vessel work-ing at the Balmoral oilfield,225km north-east of Aberdeen. Avery demanding specificationmeant that a radome could notbe used for protection. Toachieve the required pointingaccuracy of 0.05° for the antennatracking and pointing system inthe fierce wind conditions theantenna mount is made veryrugged and position -controlledby a servo system using multipleprocessors.

This system receives error sig-nals from two sources. Dynamicvariations are sensed by an atti-tude and heading reference unitwhile slow drifts are obtainedfrom a step -track pattern. Aninput to the step -track system isprovided by a receiver picking upsignals from a beacon on thesatellite. The two correctionsobtained through these detec-tion systems are combined andthen used to control the anten-na's azimuth and elevationmotor drives.

Overall the floating satcomterminal provides voice and datacommunications at Ku bandthrough the European ECS-2space segment to a British Tele-com shore station at Bridge ofDon, Aberdeen. Transmitter r.f.power is 250 watts. Multiplechannels are obtained by thes.c.p.c. (single channel per car-rier) transmission method, a sys-tem widely used in satcoms forsending a large number of differ-ent voice or data signals througha single transponder. Modula-tion is by companded f.m.

Ten voice channels are initial-ly available, with an option forexpansion to 25 channels with-out alteration to the equipment.Data is transmitted in 64Kbit/scircuits but with a Viterbi systemof coding which results in anactual transmission rate of about132Kbit/s. Considerable use ismade of voice digitizing and sta-tistical multiplexing to achievethe highest possible transmis-sion efficiency. Equipment re-dundancy is applied throughout.

It seems that the Balmoral

oilfield is a 'marginal' one fromthe business point of view, with aprospect of high recovery costsand small returns. Combinedwith the recent oil price drop,this makes a difficult situationfor the suppliers of communica-tions equipment, as the oil com-panies don't have much moneyto spare for capital investment atthe moment.


INTELSAT has elected His Excel-lency Susanta De Alwis, the SriLankan ambassador to the USA.as the new chairman of the inter-national cooperative. He is sup-ported by Juan Ciminari ofArgentina, who was elected vice-chairman at the same time. MrCiminari, who has a degree inelectronic engineering, hasworked for Motorola in Argen-tina and served as that country'sSecretary of Communications.

After the somewhat dramaticdismissal of its previous directorgeneral (and his deputy) follow-ing an audit, INTELSAT has nowappointed Dean Burch of theUSA to this important post for aterm of six years. A lawyer byprofession, Mr Burch has had 30years' experience in telecom-munications, including chair-manship of the FCC and lead-ership of the US delegation to the1985 WARC at Geneva.

Newly elected chairman of thecouncil of INMARSAT is a Britishcommunications engineer, GeoffHall. He is currently head ofsatellite systems (planning andpolicy) in British Telecom Inter-national. In 1966 Mr Hall was incharge of the early UK satcomservices operated through thecountry's first earth station atGoonhilly. Later he worked forthe Comsat Corporation in theUSA and was involved in theestablishment of the INTELSATorganization. After his return tothe UK, Mr Hall was given re-sponsibility for all BT earth sta-tions in this country.

He served as the INMARSATcouncil vice-chairman in 1986.Taking over this position now isHideo Nagata, director of thesatellite and radio communica-tions department of KokusaiDenshin Denwa of Japan.

Satellite Systems was written byTom Ivall.


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Crossover distortion inclass B amplifiers

Detailed tests on three modes of amplifier operation, includinga non -switching class B type, using the same basic circuit

produce a few surprises.

Ever since the publication of my circuitideal I have received questions as towhat extent the circuit was an

improvement over the traditional arrangement. Nearly every question emphasized thesubjective sensation of distortion reductionachieved'.

At the time I had measured the circuitperformance and found that the circuitdefinitely posessed certain advantages tojustify publication, but enough data wascollected to give a precise answer (other than"come and listen for yourselves").

Now I can give some answers regardingelectrical performance and offer some hintson what can be perceived. There are stillunknowns however and further experimentsare encouraged to throw more light on thesubject.


Historically, crossover distortion was thefirst distortion mechanism encountered intransistorized audio amplifiers ("transistorsound"). It was considerably reduced byemploying the now common bias technique'sand it is surprising how little attention it hasreceived in literature since. By the discoveryand explanation of other distortionmechanisms it eventually faded into thebackground until the famous feedback vsfeedforward error -correction debate.followed by the subjective evaluation debate.Although subjective evaluation wasrecognised to produce statistically unusableresults', there remained an impression thatnot everything could be measured tocorrelate with the descriptions of what hasbeen perceived by the "golden eared" ones.In fact there are many works that stress theoutput stage non-linearities as the majorsource of problems (refs

Various methods have been developed toevaluate amplifier distortion. Most of themuse steady-state signals to aid analysis.Several forms of distortion, however, havetheir origin in conditions that are variable bydefinition ("What have sine waves to do withmusic?").

Having experimented with different

Sync in



Signal in


Amplifierunder test

Trigger Plot xTransiert

Signal recorde-

Datalab OL 905; X



ionI See appendix In

Phase tuning


334 /











Fig.1. The "subtraction" test set-up due to Baxandall can be used with both steady-stateand transient signals and does not require a precision reference.

methods I finally decided that the'subtraction' methods' could offer most inflexibility as it requires no precision signalreference and can be used with both steady-state and transient signals.

Fig. 1 shows the test circuit. while Fig. 2shows the experimental amplifier built toenable comparative measurements betweenstandard class A and class B circuits and thecircuit proposed' which will be referred to asclass NSB (non -switching Bl. The circuitshown in Fig. 2 has the advantage of usingthe same devices in all the three modes, thusenabling direct comparison of test results.The front-end was built around a 5534operational amplifier with open -loop gain of60dB. unity -gain compensated by 22pF. a20dB closed -loop gain. 40dB overallfeedback and 200kHz closed -loop roll -off.The experimental amplifier performance iscompared to another 5534 as its basicperformance was considered acceptable by

power amplifier standards. This amplifierhas also a high -frequency single -polenetwork which matches its high -frequencyroll -off and phase to the experimentalamplifier. The output signals of bothamplifiers are summed together by aresistive network. Being of opposite phase.the output signals are effectively subtracted.leaving only noise and distortion at thenulling point. A further 5534 is used toprevent nulling point loading by other testequipment and to amplify the error signal( x 10) to increase the level as required by theinput sensitivity of the test equipment.

Using a sine -wave generator at first to testthe class B performance it was noted that ifthe level of distortion was changed thehigh -frequency single -pole control had to bereadjusted to give minimum output fromthe subtraction amplifier (Fig. 31. Toinvestigate the pattern of the change thegenerator was replaced by the circuit shown


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in Fig. 4, consisting of a square -wavegenerator driving two tunable band-passfilters both with independent Q -factoradjustment. At high Q settings the filtersproduce exponentially decaying sine wavessimulating a real -life transient (Fig. 5, toptrace). Such a signal offers the advantage oflooking simultaneously at both distortedand undistorted amplifier response andmake direct comparison.

By trying to get minimum output fromthe error amplifier it was noted that if thephase was nulled in the high signal levelregion where crossover spikes occured thereremained considerable phase error in thelow-level region where no switchingdistortion was being produced (Fig. 5,middle trace). And vice versa: if the phasewas nulled in the undistorted region a lot ofuncompensated phase error appeared.broken by the crossover spikes (Fig. 5.bottom trace). This means that only whenthe output signal amplitude falls below thelevel of transistor cut-off both amplitude andphase effects can be cancelled completely.Increasing quiescent current considerablyreduced both phase error and crossoverspikes, but they could not be entirelyeliminated until the quiescent current wasgreater than the peak output current(essentially class A operation).

The obvious explanation is that when theclass B output stage generates distortion thevoltage gain stage is having a hard job torebalance the error sensed by feedback, butit can only react with its own open -loop

Fig.2. The experimental amplifier circuitdiagram function in three modes, A, B andnon -switching B.


bandwidth and gain7. Also, the outputimpedance, being not near -zero underdistortion conditions, forms an attenuator.together with the load which becomes partof the feedback loop. This is confirmed byFig. 6 which shows error increase undercapacitive load.

The degree and nature of distortion inclass B configuration was a real surprise forit was expected that high distortion wouldshow up at levels where the inactive outputdevice becomes unbiased and eventuallyreverse biased (Fig. 7, top trace). That is alsowhy it was expected that class NSB bias mode(Fig. 7, bottom trace) could be a bettersolution. In fact, in Fig. 8, where voltagesacross the output emitter resistances arerecorded, the distortion threshold is reached

when the output level falls below 100mV (on4 ohm load, 0.4 ohm emitter resistances and100 mA quiescent current).

It was also found that distortion falls asthe voltage gain stage bandwidth rises,which was expecteds. This throws a bit morelight to schemes of alternative frequencycompensation networks9 and local errorcorrection techniques19.11. While thosemethods reduce the errors considerably, theproposed circuit eliminates them inprinciple, enabling the overall feedback to bealways effective. Comparing the recordedclass B performance with class NSB recordedin Figs 9 & 10 shows the distortiongenerated with class NSB operation is veryclose to the noise floor. These figures are thesame as can be achieved with class A

Fig.3. Class Boperation: Outputsignal, top trace.2V/div. Errorsignal, middletrace, 10mV/div.Decreasingquiescent currentfrom 100 to 20mAincreasescrossover spikesand phase must bereadjusted.bottom trace,10mV/div.Recorded withresistive load.timebase 2ms fullscale.




Systems p

measurement I 'T




3k 30k


BC 212









BC 287



BC 182

BC 212


BC 286



S 04

e w 68


BC 287-"\AA.,

7k5.12F7 :5

BC 286 1k


62 S1B

BC 286




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operation. Such performance speaks foritself.

The proposed class NSB circuit has severaldistinct advantages over similar circuitspresented before''. First, it uses onlynegative feedback (in contrast to positive orcombined positive and negative in similarcircuits) to sense and prevent switching off(Fig. 7, bottom trace). Secondly, thequiescent current is sensed directly, thus nothermal feedback is needed to achievethermal stability. Third. thermal stability ofthe circuit does not rely mainly on highvalue of emitter degeneration resistance, sothose resistances can be made small (lessthan 0.1 ohm) and so improve outputimpedance linearity in dependance of outputcurrent.

2 Hzsquare





5k Hzlow-pass

f! [ter

Fig.4. Test signal generator block diagram.

50 m\

Fig.5. With exponentially decaying sine wave both distorted andundistorted class B response can be compared simultaneously.Top trace: test amplifier output. 2V/div. Middle trace: phase nulledin distorted region shows uncompensated phase in undistorted



50u re-

Fig.7. In class B operation the inactive output device becomesreverse biased: the output voltage is compared to the bias voltageunder quiescent condition and with input signal applied, toptraces. 2V/div. No such condition is allowed in class NSB operation,bottom traces, 2V/div. Resistive load, timebase 0.5ms full scale.

201. H


0(decayadj I



2k Hzband-pass



1.-L F amplitude






50 mV





50 J)1 VV I 4.114

I\region, 50mV/div. Bottom trace: correct phase nulling, 5OmV/div.Resistive load, timebase 0.5ms full scale.Fig.6. above. Same as in Fig. 5, except bottom trace recorded withcapacitive load. showing increased phase error.


50 mV--




Fig.8. Class B output transistor currents (recorded as voltagesacross the emitter resistors) with zero current level shown forcomparison. Vertical sensitivity 50mV/div., R(e) = 0.4ohm. R(L)4.Oohm. 1(q) = 100mA. Bottom trace shows the error signal at2OmV/div. Time base: 2ms full scale.


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-0. If I

Fig.9. Class NSB operation with 100mA quiescent current shows notrace of phase error and no crossover spikes. Top trace: 2V/div.,middle trace: 0.1mV/div., resistive load, bottom trace: 1.OmV/div.,capacitive load, timebase: 0.5ms full scale.


Fig.10. Same as Fig.9 except bottom trace 0.1mVicliv. recordedwith capacitive load: timebase 5ms full scale.


Although further investigation is neededseveral conclusions can be readily drawnfrom the data presented:

Class B amplifier generates crossoverdistortion until the output signal currentfalls below the level determinated by theratio of load impedance to emitterdegeneration resistances and quiescentcurrent setting.

When crossover spikes are present aphase error is also generated'.

Phase error is inversely proportional tothe open -loop bandwidth of the voltagegain stage.

Phase error is also dependent on the ratioof the amplifier output impedance to theload impedance.

The envelope of the phase error signalstays in fixed proportion to the outputsignal envelope until a threshold isreached and it suddenly disappears(switching phase modulation).

In complex signals the individualcomponents are differently affected: thehigher the frequency, the greater thephase error. This, and the previous pointmean that phase coherence is lost duringthat part of a musical signal which bearsdominant localization and 'definition'information.

A cost and bias level compromisecombined with thermal stabilityrequirement has forced many designersof commercially equipment to underbiasthe output stage (for comparison, see ref.8).

As a consequence, comparing amplifiers ofdifferent design shows differences thatdepend on open -loop bandwidth and gain aswell as on output impedance and quiescentcurrent setting. Also, using the same loud-speaker load doesn't guarantee freedomfrom load -induced differences.

Regarding audibility of the describedperformance bear in mind that manysubjective evaluation sessions have reportedobjections which could be attributed to lost

phase coherence. Unfortunately, I have nomeans of performing a well -controlledlistening session; someone with moreexperience in this field is invited to contri-bute. Of course, when listening tosome digitally recorded piano I coulddefinitely express my preference for classes Aand NSB performance, even though notbelonging to the "golden eared" category,but the opinion of a single person land astrongly biased one who also knows what tolisten for) can hardly have statisticalmeaning.

In fact, the phase errors recorded are ofthe order of 0.05 degrees at middlefrequencies increasing up to several degreesat the top of the audio range, measured witha resistive load. Reactive loads and/orreduced open -loop bandwidth produces evengreater phase error but to standardizemeasurement a reference reactive load andbandwidth are required to be defined.

But equally important, a statisticallymeaningful definition of the audibilitythreshold to switching phase modulationwould be welcome. Only in regard to thisthreshold can the data presented hereundergo relevant evaluation.

Finally, it has been demonstrated thatboth class A and class NSB are free from theeffect described, thus highlighting theinherent quality of the NSB principle as asolution for crossover distortion.

References1. E. Margan. Add-on current dumping,

Electronics & Wireless World. 1985, October,p.40.

2. G. Nalty. Feedback letter. Electronics &Wireless World. 1986. February. p.42.

3. M. Clogolja, "Biasing circuit for the outputstage of a power amplifier - the Vh.multiplier". RCA application note AN 6297.

4. S. P. Lipsh*tz and J. Vanderkooy, "The greatdebate: subjective evaluation", Journal of theAudio Engineering Society. 1981, July -August, p.482.

5. P. Blomley, New approach to class B amplifierdesign, Wireless World. 1971, February, p.57,March. p.127.G. C. Haas. Design factors and considerationsin full complementary symmetry audio power

amplifiers, Journal of the Audio EngineeringSociety, 1968, July, p.321.N. S. Pass, Active bias circuit for operatingpush-pull amplifiers in class A mode. USPatent 3 995 228.1976, November 30.

6. P. J. Baxandall, Audible amplifier distortion isnot a mystery, Wireless World. 1977.November, p.63.

7. M. Otala, Nonlinear distortion in audioamplifiers, Wireless World. 1977. January,p.41.

8. J. Lohstroh & M. Otala, An audio poweramplifier for ultimate quality requirements.

acoustics, 1973, December, vol. AU -21. no. 6.p.545.

9. E. M. Cherry, Nested differentiating feedbackloops in simple audio power amplifiers.Journal of the Audio Engineering Society.1982. May, p.295.

10. M. J. Hawksford. Distortion correction inaudio power amplifiers, Journal of the AudioEngineering Society. 1981. January -February, p.27.

11. M. J. Hawksford. Distortion correctioncircuits for audio amplifiers, Journal of theAudio Engineering Society. 1981, July -August, p.503.M. J. Hawksford, Optimisation of theamplified -diode bias circuit for audioamplifiers, Journal of the Audio EngineeringSociety. 1984, January -February. p.31.

12. S. Tanaka, New biasing circuit for class Boperation, Journal of the Audio EngineeringSociety, 1981. March, p.148.

13. E. M. Cherry, a new distortion mechanism inclass B amplifier, Journal of the AudioEngineering Society. 1981. May. p.327.

Appendix 1 - Phase error calculationThe error signal undergoes phase modulationduring the first rising edge of the output signal.Fig 5. whereupon a fixed phase relationship isestablished. If we neglect the exponential ampli-tude decay term as it is present in both the inputand output signal as well as in the error signal, andlabel the input signal as sine, then the error signalis clearly a cosine. Looking at the amplitudenulling network under the correct nulling condi-tion:

reference signaloutput signalerror signal

turn to page 709

x=Asinwt= B sin bot+e)

z = C cos wt


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NEW PRODUCTSSynthesizedfunction generatorA fully programmable 2MHzsynthesizer/function generator withhigh 30V peak -to -peak output andeight -digit resolution has beenintroduced by Philips Test &Measurement.

High output accuracy andrepeatability is guaranteed in thePM5191 by direct synthesis of anoutput signal from a crystaloscillator reference, ensuring thatthe stability is as good as that of thecrystal. Phase noise is less than80dBc/Hz.

Sinewaves, triangular signals,pulse trains and positive and negativeramps are the five outputs provided,with amplitude modulation beingpossible both internally andexternally. The high output voltagecan be set in r.m.s, peak -to -peak ordBm. a.c. and d.c. settings arecompletely independent within the± 15V window.

Manual operation is designed to hesimple, with logical grouping of frontpanel controls and clear led readoutof waveform, frequency and outputsetting. Frequency -related settingscan be made precisely with numerickeys while preset frequency and levelsteps can be accessed by up/downbuttons. The instrument can beoperated remotely through a GPIBan incorporated into an automatictest system. Pye Unicam Ltd. YorkStreet. Cambridge, CBI 2PX. Tel:0223 358866.

Spectrum and logicanalysers for hireInstrument Rental now have two ofthe newest offerings from Tektronix.The 2710 is a low cost highperformance spectrum analysercovering the range 10101z to1.8GHz. Due to the user-friendlydisplay and no less than five separateparameter menus, the instrument'soperation and set-up procedure isboth quick and easy. Featuresinclude a marker mode to give directreadout of frequency and amplitude,automatic signal centering, userdefinable key steps, and waveformstorage of up to three separate traces.

The Tektronix 1225 is a new logicanalyser. It consists of 48 channelsrunning at speeds of up to 100MHz inasynchronous mode. Like the 2710,the 1225 is extensively menu drivenwith the bArt. Illitlir111111 vr«,ntrnl,

for data entry and function selection.Features include glitch capture.multiple time bases, 2K of memoryper channel, built in battery backed,real-time clock and non-volatilestorage for eight front -panel set ups.Instrument Rentals (UK) Ltd,Dorcan House, Meadfield Road,Langley. Berks. SL3 8AL. Tel: 075344878.

Static testerreaches 25kVSchaffner EMC's latest electrostaticdischarge tester, the NSG 432, willgive test voltages of up to ±25kV.Part of the expanded NSG 430 seriesof test equipment, the new tester hasa multi -turn potentiometer to enablesetting the voltage with betterresolution, from a minimum value of2k1': hot rther than rely (.n the

potentiometer's linearity, thedesigners of the 432 haveincorporated a digital voltmeter. Allmajor test standards are catered forby the increased output available.

The instrument is supplied with ahuman -body model simulation toIEC801-2 (150 ohms, 150pF), butother models can be simulated onrequest. The purchaser may specifypositive or negative polarity (positiveis standard), an E -field adaptor or anH -field generator which produces anassociated burst of electromagneticradiation. For semi -automatictesting. there is an optional counterwhich produces a preset number ofdischarges in succession. The NSG432 has been designed so that futurechanges in standards can be met bysimple modifications. SchaffnerEMC Ltd. Headley Park Area 10,I leadley Road East, Woodley,Reading. RG5 45W. Tel: 0734697179.

NEXT MONTHOptical fibres. Short -haul optical-tihi edata communication is an essential partof modern communications systems.This feature presents an overview of thetechniques employed and the hardwareavailable.

Pioneers. Next in this gallery of thefounding fathers of electricalcommunication is Oliver Heaviside, theirascible genius whose insight into thephysics of cables made long-distancetelephone calls a practical possibility.

Tone generation system. Amicrocomputer scans two electronicorgan keyboards and a pedal board,controlling up to 15 generators, whichcontain eproms holding the waveformscorresponding to 16 different stops.Attack and decay times are appropriatefor each frequency and tone colour.

Q and stability. A further look at Q, withreference to the stability of oscillatorsused in timekeeping.



Short -hauloptical fibres

Heaviside -champion ofinductance

Curls, divs,vectors andscalars


Variable -speed, C -format v.t.rs


(Allis and divs. Having mentionedMaxwell recently, /W finds himselftaken to task for not explaining vectorfields. It turns out to be not too difficultand certainly not stodgy.

A new look at gain/bandwidth product.The received wisdom is that the gain/b.w. product of a feedback amplifier is aconstant, with reduced bandwidth athigh gains. Is this true, or is it simply amatter of circuit design?

Variable -speed video. In the three yearssince our original series of articles onthis subject appeared, the technique ofreplaying C -format professional v.t.rs atvariable speed has advanced. JohnWatkinson deals with the newdevelopments.

Image localization. Using the wavefrontreconstruction approach to predictimage position in stereophonic soundsystems with interchannel phasedifference.


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Credit card memoryThe Aston Card has been given manyadditional applications. This credit-card sized memory plugs intoequipment designed to use it or intoa special adaptor to provide additionram. rom or eprom to a computer orother digital device. An adaptor andplug-in p.c.b. has made it suitable forthe IBM PC in addition to theadaptors already available for anumber of other computersincluding the BBC, Commodore andAmstrad micros. Originally foundedaround eproms. the range has nowbeen extended to include lithium -hacked static ram (up to 1Mbyte) andeproms. either of which can be usedas a removable. solid-state, disc -likestorage medium. Software providedwith the system allows the cards to beformatted and the computer willtreat them as if they were discs.Masked roms for specific applicationscan he produced.

A 4-4, too

Some applications are securityaccess, remote data capture andevent recording, font and characterchanging in printers, software forprogrammable machines and so on.Further details from Cumana Ltd.The Pines Trading Estate. BroadStreet. Guildford. Surrey CU3 3B11.Tel: 0483 503121.

1Mbit dynamic ramsHigh speed and low power are thelatest developments in Toshiba ramswith packaging in standard dual -in -line. plastic SOJ and ZIP formats forapplications flexibility.

The new TC5110110P/185 featuresan access time of 85ns and a page -mode cycle time down to 50ns. Thedevice is suitable for high-speedmicroprocessors operating at up to16MHz.

The TC514256PL has an operatingpower figure of 358mW reducing to5.5mW on standby. Access time is10Ons. As the standby current is lessthan 11)(11.1.A this device can replacec.mos rams in large battery -hackedmemory arrays. Toshiba (UK)Limited. Semiconductor Division.Frimley Road, Frimley. Camberley,Surrey. (a116 511. Tel: 0276 62222.

Spectrum analyser fromRohde & SchwartzThe FSA (Frequency SpectrumAnalyser) from Rohde & Schwartzoffers a dynamic range of 150dBm ina 611z resolution bandwidth.Covering a frequency range 100Hz to1.8 or 2GHz, the FSA meets mostrequirements for the measurementof spectral distribution of signals.The quasi -continuous i.f. resolutionand synthesiser tuning render theinstrument suitable for both sweptand fixed frequency analysis. Allfunctions can be remotely controlledvia the GPIB bus: thus ensuringsimple integration into larger testsystems.

The FSA facilitates the highestavailable frequency accuracy by theuse of synthesisers throughout theinstrument. With bands above5M11z; synchronized start and stoptechniques are employed - smallerbands use phase synchronizedfrequency steps. The FSA offers anintermodulation-free range of>100dB together with low s.s.b.phase noise of < -114dBc at 1KHzfrom the carrier. The resolutionbandwidths: typically 611z to 3M11z;the frequency span 1001Iz to 2GHz

and the level display range of 175dB( -145 to 30dBm) make the FSA idealfor all applications of selective levelmeasurement.

The FSA offers high operatingconvenience with parametervariation via step keys, direct entry.spinwheel or menu -dependentsoftkey operation. Automatic testroutines include correction routinesfor level, frequency and bandwidth,internal self -test, adjustableautomatic coupling for resolutionbandwidth, video bandwidth andsweep time, help functions,autozoom and autoranging. The FSAincorporates a 9in (228mm) colourmonitor with free choice of coloursfor traces; graticule; softkey labellingand background. Further features ofthe FSA are a.c./d.c. coupling;integrated a.m./f.m. demodulatorand loudspeaker; Centronicsinterface and user port. Alsoconnectors for external monitor;headphones and keyboard. Rohde &Schwarz UK Ltd. Roebuck Road,Chessington. Surrey KT9 1LP. Tel:01 397 8771.

Tailor-made connectionsFlexicon have set up a full-timespecial -projects team for bespokeconnectors. Among their recentproducts is a low -profile chip -carriersocket which uses elastomericinterconnections to provide up to224 ways. The socket projects only2mm above the surface of the p.c.b.and can be surface mounted. Holesare needed for the fixing andorientation of the socket. Mountingthe chip exerts a minimum of stressand distortion to the p.c.b. Thedesign ensures correct polarity andorientation during assembly.

Other specialist connectors havebeen a zero -insertion -forceinterconnection system for flat -screen display panels and a high -density low -profile connector for theexpansion modules of the CambridgeComputer's (Sir Clive Sinclair's) Z88computer.

The company believes that there isan increasing market for bespokeconnectors which are designed into asystem rather than being added as anafterthought. Flexicon Systems Ltd.Hitchin Street, Biggleswade, BedsSG18 8BH. Tel: 0767 312086.

GTO snubbercapacitorsSnubber capacitors are designed tocarty the full load during the turn-offperiod in gate -turn-off thyristors.The capacitors produced by LCRComponents have a peak currentrating of 2000A. The very short turn-off phase of some applicationsrequires the capacitors to have a lowinductance of about 30nH, highr.m.s. current carrying capacity of75A and a high dv/dt pulse rating of2000V/p.s. The capacitors areavailable in the range 1.5 to 4mFwith tolerances of ±5 and ± 10%.LCR claims to produce the largestrange of capacitors in the UK. LCRComponents. Woodfield Works.Tredegar, Gwent NP2 4BH.Tel: 049525 3131.

Surface -mountedresitors andinductorsBICC Citec have produced a numberof surface -mounted resistive andinductive components.

The 3204 is a fully sealed chippotentiometer, suitable for dip orwave soldering. Range available isfrom 5000 to 1MO. with a powerrating of 0.1W at an operatingvoltage of 20V.

Resistance in the 3305 trimmerpotentiometer ranges from 10 to2M0. It is believed to be the first fully0 -ring sealed chip trimmer. It has apower rating of 0.25W at 70°C withan input voltage of 20V. Temperaturestability is within 100p.p.m.

Also available on 12mm-tape reelsis the 3600 range of chip inductors.with a range from 0.22p. to 220mH.with an operating temperature from-25 to +85°C. A tolerance of 10% isoffered on values above 3.3mH.

Citec has also produced chipresistors and resistor networks forsurface mounting. BICC-Citec Ltd.Westmead, Swindon. Wilts. SN57YT. Tel: 0793 478301.


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FORTHSFor IBM PC and CompatiblesModular Forth - award winning Forth 83 £475.00very fast, multitasking, GEM, modules, 8087 fpWorkFORTH

Viewtrace DebuggerSoftware Floating Point80 x 87 Floating PointWindows & GraphicsDocumentation Tool Kit

WorkFORTH Development Kitincludes ViewTrace, SoftFP, Doc Tools

For 680 0 SystemsMPE-Forth/68K 0S9/68K - fastMPE-Forth/68K CPM/68K - fastGEM-Forth/ST Atari ST - GEM i/f, fastMVP - Forth AmigaMM MasterForth MacintoshOthersUniForth for RT11, RSX11, VMS

(inc micro)







aTel: 0703 631441

Software & Tools for EngineersCROSS -COMPILERSFor PCDOS, MSDOS, 0S9/68K, CPM/68KCPM80. OS9/6809, FLEXfor generating new Forth applications, includingROM based turnkey systems fast, interactive,debuggable code, high or low level interrupts,technical support, source code, debug &download tools, cross assembler included.Practical solutions to real problems.Cross Compiler core £250

Targets include source, RAM and ROM versionsForth -83 targets £225

Z80, 80 x 86/8, 680 x 0Fig -Forth targets £175

6502/110, 8080/5, Z80/64180, 80 x 86/8,1802, Z8, 6800/6303, 6809, 680 x 0, 99xxx

Forth -79 targets £350Bryte Forth 8031/44/51

HARDWARE for PCsEPROM Programmer 2716-27512 £145PAL Programmer MMI, NS, TI 20/24 pin £325GALJEPLD Programmer Lattice/Altera

20/24 pin £350NOVIX 5Mips co -processor - ready for

NC5000MVP Microcoded - includes microcode tools £1225


ENT12.1t 51 ON It F.I'LY CAM)

'Ac sell all types of test equipment fromthe simplest to the most sophisticated andspecial ised.

All of the high quality second userequipment we supply is fully calibratedand meets the manufacturers originalspecification. All equipment is fullyguaranteed.

We also buy good quality under utilisedequipment.


Used Test Iguipmern

Mock lionAutumn 19114

01-4) lonry





For further details contact

HARRISON ELECTRONICSCentury Way March Cambs PE 15 80W Tel 10354151289

IC OMCommunications

ICOM introduces the II' F. )oc advanced technology cciitiiiiiocscommunications recer:--! With 99 programmable memories he IC-P7C,Ycovers aircraft marine FM nroadcast Amateur radio television and weathersatellite bands For simplified operation and quick tuning the 1C -R7000 featuresdirect keyboard entry Precise frequencies can be selected by pushing thedigit keys in sequerce of the frequency or by turning the main tuning knobFM Nide FM narrow AM upper and lower SSB modes with 6 tuning speeds

I 0 5 10 12 5 and 25kHz A sophisticated scanning system provides instantaccess to the most used frquencies By depressing the Auto -M switch theIC -F7000 automatically mertorises frequencies that are in use whilst it is in thescan mode this allows you /o recall frequencies that were in use Readout isclearly shown on a dual-col bur fluorescent display 0p' -7., PC -12infra -red remote controller voice synthesizer and HP -

release rush me details of the IC -R7000 and my nearest ICOM dealerName



LHerne Bay, Kent CT6 8BR. (no stamp) Tel 0227363859. -F:NTrAt 29 ON IO:PLY ('.\ Itl)


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LANGREX SUPPLIES LTDClimax House, Fallsbrook Rd., Streatham, London SW16 6ED

RST Tel : 01-677 2424 Telex :946708 RSTSEMICONDUCTORS IP// 11


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('rice ruling al time of despatch.In sonic cases prices of Mullard and l'SA salves will he higher than those ads ertised Prices correct u hen going to press.Account facilities aallable to approsed companies with minimum order charge 1111 Carnage and packing 11 .non credit orders(her 111111101)pes of s als es. tuhes and semiconductors in stock Quotations for any Is pes mil listed. S A E.

Telephone 01-677 2424 7Telex: 946708E. & 0.E.Open to callers Monday -Friday 9 a.m. - 5 p.m. WW



& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (85)

STEW PRODUCTSPiezoelectric filmPolyvinylidene fluoride Ipvd0 in apolarized form, with metallicconductive surfaces applied, offersremarkable piezoelectric propertiesand may be used for a seeminglyunlimited number of applications intransducers. It acts as a self -chargingcapacitor with the signal taken fromthe metal electrodes. Like piezo-ceramic material, it produces anoutput voltage when stressed andwill change its physical dimensionswhen a voltage is applied across it: soit can he used both for microphonesand loudspeakers. As a load cell it canhe used in pressure. strain, vibrationand impact measurement. and inaccelerometers. It has been used toprovide touch sensors forexperimental robots. and respirationand heartbeat sensors for babies. Thesimplest example is its use as a switchand with 20 times the output of aceramic transducer, proportional tothe applied stress, it can drive aliquid -crystal display directly. Thefilm can be incorporated intokeyboards where the switches havethe advantage of dirt and moistureresistance, bipolar output and theability to be used in battery -poweredequipment. One specific successfulapplication has been in itsincorporation into a pressure -sensitive graphics input tablet withan x -y accuracy of 0.1mm.

1 he film also responds to infra -redradiation and can be used fortemperature measurement. It issensitive enough to detect a humanbody at 16 metres and beincorporated into intruder alarms.Further details, samples.experimentation kits and the filmitself are available from the PennwaltCorporation. 74 Great King Street.Edinburgh E113 6QU. Tel: 031 5581144.

Solder reworkstationA new 11 cl ler multi -function hot gasworkstati. in is suited to rework andreflow soldering/desoldering ofmicro components. The Al 11700station features a hot -gas pencil.giving a variable rate of gas flow, thetemperature of which is adjustablebetween 10°C and i50°C. Gas flow isturned on and off by means of afootswitch. A hand-held vacuumpick-up tool, connected to the workstation. enables components to hepositioned or removed during reflowor desoldering. A temperaturecontrolled hot plate. adjustablebetween 30 and 250°C provides pre-heating for ceramic or othercomponents with poor heatconductivity. Weller equipmentcomes from Cooper Tools Ltd.Sedling Road. Wear. Washington.Tyne and Wear N38 9132. Tel: 091 416


Fast charging of NiCadsAfter extensive research into thebehaviour of nickel cadmiumbatteries under various pulsedcharging conditions. Rediffusionradio systems have developed aprocessor -controlled battery chargerthat is capable of sensing thecondition of the battery andrecharging it accordingly. It isintended for use with the smallerNiCd batteries commonly used inhand-held radios and other battery -operated equipment as used bypublic and emergency services.

At the heart of the BC25 charger isa patented system for recognizingthe fully charged state of a battery.Having this ability, the charger canhe used to rapidly charge each

battery safely with no risk ofovercharging. It can also he used totrickle -charge batteries only partlydischarged. A full condition charge.i.e. a controlled discharge followedby a rapid recharge. is used forbatteries that have failed or may hesuspect. I.eds are used to indicate thestatus of each battery under chargeand, in the condition mode, thecapacity of the battery as apercentage of its rated capacity. TheBC25 is fully automatic and onlyneeds the batteries to he loaded andremoved. A manual switch alternatesbetween normal or conditioncharging. Rediffusion Radio SystemsLtd. Newton Road. Crawley, WestSussex. RI110 2PY. Tel: 0293 518855.

Pulse/echo cable fault locatorThe first truly hand-held. battery -powered, pulse -echo cable faultlocator with I.c.d. read-out is claimedby Cossor. It has been designed to hecomfortable and easy to use by anyoperator. The CFI. 510 us&microprocessor technolgy and theI.c.d. is a dot matrix type with fourranges: 100m. 300m. 1000m and3000m full-scale. with 1.6%resolution and a nominal 3%

accuracy.The pulse width is selected with

each range and velocity factor set to0.67 at switch -on and is adjustablebetween 0.01 and 0.99. With a weight(4 only 1 kg. the CFL 510 is poweredby six AA cells with a battery life of upto three months normal usage.Cossor Electronics Ltd. ThePinnacles. Harlow. Essex CM I9 31313.Tel: 0279 26862.

Graphic chip setNew from Ili-Tek Electronics is theNational Semiconductor advancedgraphics chip set, a v.l.s.i. systemwhich utilizes parallel processingtechniques to enable handling of anunlimited range of colours with noreduction in performance.

The chip set comprises individualmodules which enable the user todesign a system to meet specificrequirements. Modules can heintegrated with a general-purposemicroprocessor for black and whitedisplay or used to support unlimitedcolour planes for a highperformance, high resolution colourgraphics workstation. plotter, orprinter.

Modules in the chip set include a20MHz raster graphics processortr.g.p.) which has line drawingspeeds of 10 million pixel/s in anydirection and a powerful instructionset, enabling the user to incorporateproprietary graphics algorithms intothe system: a 20MHz 'habit'processing chip which, dedicated to asingle parallel memory plane.enables additional planes of colour tohe added without degrading systemperformance: a video clock generatorwhich uses a low -frequency crystaloscillator and an on -chip digitalphase -locked loop to produce a pixelfrequency of up to 225MHz: and a225MHz video shift register whichhas a 4 -word 16 -bit fifo buffer to easetiming problems.lii-Tek Electronics.Ditton Walk. Cambridge. CB5 8QD.Tel: 0223 214722.

Low -profile toroidsTo meet a demand for compact powersupplies and audio equipment. DrakeTransformers have developed a rangeof low -profile toroidal transformers.The PWL range has about half theheight of conventional toroids withequivalent ratings hut have a greateroutside diameter. They havepolyester tape insulation and sleevedflying leads. The PWL transformersare offered in a range from 100 to800VA.

Drake is now an independentcompany. having bought itself fromits former parent. BlagdenIndustries. This has resulted inmaintaining employment for 76skilled workers. while moving to anew address near their formerfactory in Billericay. DrakeTransformers Ltd. Bruce Grove.Wickford. Essex SS11 8BT. Tel: 0268560040.


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (86)



High-speed 10 -bitd -to -aTwo ultra -high-speed digital -to -analogue converters have beenproduced by Datel. The ADC -510and 515 can complete a 10 -bitconversion in 425ns and 650ns.giving sampling rates of 2.35 and1.54MHz respectively.

Features include initial errorsof 3 I.s.b. maximum for offsetand 51.s.b. maximum for gainerrors, different codingselections, indication of signalsbelow and above the full-scalerange and the means to improvethroughput by putting a sample -hold hack into the sample modebefore the existing conversion isfinished. There is a facility toprogramme the input voltagerange. Other specificationsinclude a maximum nonlinearityof ± 0.5 I.s.h, a minimumharmonic distortion below fullscale of 60dB, and hightemperature stability. Moreinformation from: Datel UK,Intec 2 Business Park, WadeRoad, Basingstoke. Hants.RG24 ONE. Tel: 0256 469085.

Eraseableprogrammablelogic arrayAn eeprom-based programmablelogic device from Exar is claimed tohave logic capabilities comparablewith gate arrays and allows the use ofmulti -layer logic. The XR-78C800contains the equivalent of 600 to 800gates. Advanced logic architecturepermits umlimited Boolean levelswith up to ten flip-flops at any levelwithout using i/o pins. Term sharingat any level and logic -controlledinput latching are other features.The devices are designed to integratea wide variety of user -defined logicfunctions onto a single package andoffer a fast turnaround to save timeand hoard space. The device is addedto a wide range of electricallyeraseable proms including two high-speed c.mos eeproms. ExarCorporation. 43 Moorhridge Road.Maidenhead. Berks. SL6 8PL. Tel:0628 783066.

Multi -purpose logic analyserThe Gould K50 can he configuredfrom the front -panel keyboard from32 channels at 25MIlz (1k samplesper channel) to eight channels at100MIlz (4k samples per channel). Itcan capture complex timing. stateand microprocessor- orientedsoftware events. including glitchesdown to 5ns. which are stored in aseperate memory and can heunambiguously displayed alongsidetiming data.

Three external clock inputs withqualifiers are provided to allow thedemultiplexing of complex events.while Gould's 'Trace Control' featureoffers four levels of complex -eventdefinition with four trigger wordsplus one glitch word.

The K50 features a high -resolution, non -glare 7 -inch(178mm) c.r.t. which can show up to17 channels across the completememory or he expanded for detailedviewing.

Channels or channel groups canbe labelled. and two independenton -screen cursors and a triggermarker are used to indicate absoluteand relative data position and value.The major instrument functions are

controlled by dedicated front -panelkeys, while soft keys guide the set-upof individual parameters. The'search' and 'compare' functionsdisplay their results as highlightedevents.

The K50 is supplied with eight -channel, high -impedance probe pods11 megohm, 5pF I. which eachprovide a t.t.l. or ±9V variable -threshold range and are protected to+50V.

The analyser is supplied completewith IEEE -488. RS -232 andCentronics ports, plus trigger, re-start and video oulputs. Alsoincluded is a battery -hacked non-volatile memory which saves thecurrent stored data. three referencedata sets and 16 set-upconfigurations.

A range of microprocessor analysispackages is available, includingdisassembler software and interfaceadaptors for the Z80. 8085, 6502,6809, 8086/8 and 680(K) processors.Price of the K50 is 12950 (plus tax).Gould Electronics Ltd.. InstrumentSystems. Roebuck Road. I lainault.Ilford. Essex. IG6Tel: 01-500 1000.

Image processing on a PCA I \vo hoard plug-in for the 1101 l'CIA RT) can create an imageprocessing workstation ideal forapplications such as machine vision,image enhancement, scientific,medical, sonar and geophysicalimage analysis, high -end graphicsarts systems and simulation/trainingsystems. Design innovationsincorporated into the MVP -ATinclude 'area -of -interest' processing.real-time image operations. non -interlaced output and a 32 -hit planeimage buffer comprising four flexible512 by 512 by 8 image buffers whichcan he used in all possiblecombinations. When combined withthe capacity to performconvolutions, averaging andsubtraction, pattern matching andmorphological transforms, this will

give the user performance previouslyavailable only at a much higher price.Other functions offered by the hoardare pan, scroll and zoom, real-timecolour frame grab from a variety ofinput sources such as RGB or NTSCColour. RS 170 monochrome. andmultiple input and output look uptables.

The optional Matrox Imager -ATpackage is specifically designed tocomplement the MVP -AT andprovides a cost-effective solution for0.e.m's planning to develop theirown software. This package containsover 150 library routines and iscallable from 'C. Fortran and PascalMicrosoft compilers. DensitronComputers I.td, Unit 4. AirportTrading Estate. Biggin I till, KentTN16 311W. Tel: 0959 76331.

Maths on a personalcomputerA new software package (MathCAD)allows the entering and solution ofmathematical equations exactly asthey would he written or printed in amaths text. In addition it can he usedlike a programming language tocompute with variables. and toproduce graphs and tables and addtext. Greek characters can be used aswell as all mathematical symbols.The software handles real andcomplex numbers and computes unitconversions and dimensionalanalysis. Functions not provided canhe defined by the user, althoughsome advanced functions such asintegration, differentiation. FastFourier transforms, cubic splineinterpretation and statistical analysisare already included. MathCADchecks for errors before it processesthe equations, looking for undefinedvariables. mismatched units.missing parentheses and the like.

MathCAD runs under MS -1)0S 2.0or higher and is therefore suitable forIBM PC (XT orAT) and compatibles.It requires 512K of ram and IBMcolour or enhanced graphics or aI lercules monochrome card. Outputis to a dot-matrix or laser printer.MathSoft International 1.td.Tamworth. Staffs, B79 713R.Tel: 082786 239.

Contact cleanersUsed to clean, lubricate and protectcontacts and edge connectors platedwith precious metals (gold, silver.palladium etc) gold Electrowipes arelint -free pads impregnated with ablend of contact -cleaner fluid andsafety solvent. Packed in sachets. thedisposable pads use a non-flammablesolvent which is claimed to he safe ondelicate components and 'sensitive'plastics. As well as removingcontamination from contactsurfaces, the pads leave a residualtrace of lubricant which increasescontact area and reduces contactresistance to a low and stable level.Another advantage is that with thelubricating properties of the wipes. itis possible to reduce the thickness ofthe precious metal plating.Electroluhe Ltd. !flakes Road.Wargrave, Berks. (;10 8AW. Tel: 073522 3014.


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (87)







PRICES RANGE FROM £79.95 to £125Call now for more information





Superb integrated Mosf et aniplitier kits with an unbeatable pedigreecircuit design by Join Linsley -Hood and engineering by HARTUltra easy assemb:y and set-up with sound quality to please the mostdiscerning listener Ideal basis for any domestic sound systems if

quality matters to jou Buy the complete kit and save pounds off theindividual component priceK300-35. 35 Watt Discount price for Complete Kit £98.79K300-45 45 Watt Discount price for Complete Kit £102.36RLH485 Reprints of Original Articles from HIFI News £1.05 no VAT

LINSLEY-HOOD SYNCHRODYNE AM RECEIVERVery high quality kit for this recent deskgn featured in Wireless World Advanced constructionsystem approved by the Author uses 3 double sided PCBs In a stacked layout for total s:ability easeof construction and minimal wiring This module will 101M the AM section of an ultra high qualityAM,FM switched bandwidth tuner to match our 300 series amplifiers Power supply and tuning gangwill be included with the FM sectionK450 JLH Synchrodyne Kit Special Price £59.95

LINSLEY-HOOD SUPER QUALITY FM TUNERThe long awaited ultra high quality FM companion to the Synchrodyne AM receiver Novel circuitleatures ready butt pre -aligned front end phase locked loop demodulator and advanced sample andhold stereo decoder Circuits featured in Electronics Today International magazine February andMarch 1987 Complete kits for FM only Of combined with the Synchrodyne are cased to match our 300Series amplifiers Send for detailsSpecial Introductory Prices. FM only version £111 69 Version to add Synchrodyne f 18.13 Bothprices roc VAT Ai post Send for details

HIGH QUALITY REPLACEMENT CASSETTE HEADSDo your tapes lack treble. A worn head could be the problem Tapeheads are constantly improving and fitting one of our latestreplacement heads could restore performance to better than new'Standard mountings fit most decks and our TC1 Test Cassette will Citmake it easy to set the azimuth spot on As we are the actualimporters you get prone parts at lowest prices All our heads aresuitable for Dolby machinesHC20 Permalloy Stereo Head Good quality standard head fitted as original equipment on manydecks £7.66HS16 Sendust Alloy Super Head Dude simply the best Longer Ide than perma boy higher output thanferrite, fantastic frequency response. E14.86H05514. Track head for auto -reverse or quadrophonic use Full specification record and play head £14.60Special Offer Stereo Fi/ P Heads £2.494 -Track Auto -Reverse Play Head £3.50HS9510 2,4 Stereo DC Erase Head £6.70H0751 E 4'4 Erase compatible with H0551 £39.70Full data on these and other heads in our range are contained in our free list

HART TRIPLE -PURPOSE TEST CASSETTE TC1One inexpensive test cassette enables you to set up VU 1Dolbyt level head azimuth antitape speed without lest equipment Vital when fitting new heads Complete with instructions £4.66

JLH DUALITY AM RADIOSets of Parts avallaale now including Short Wave coils Full kits ready later Send for list

Send for your FREE copy of our lists with full details of our complete range of KIK CorivsinentsPCBs. Cassette Heads and Decks Overseas please send 5 IRCs for Airmail Post

add V4 T ro rn once. Piistage Oflfvders up to f 10 50p f 10 to £49 I f Over f.50 II hi

ELECTRONIC KITS LTD1, Penylan Mill, Oswestry, Shropshire SY10 9AF24 hr SALES LINE (0691)652894 Please add VAT

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& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (88)


Tel: 021-474 6000

Telex No: 312242




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ECC88 200 ML8536 275 00 NAT 48 00 6608 200 7586 1 1 50ECC91 200 ML 8741 265 00 4CX350A 8700 6L6GC 4 10 7587 35 00ECC189 200 NI SERIES 45150A 33 70 6106 6 25 7591A 4 65ECF80ECF86ECF801ECH81ECL82ECL86EF80EF85E F86

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HP18IA Storage mainframeTEK7603 Mount rome 100MHz,


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TEK 7880 Delayed Timebase 400MH/TEK 7685 Delaying Timebuse


DVM'sDalton 1051 5' Digit AutorangingSolartron 1765Solomon 7065 6' : digitSolartron 7075Solartron 7050

VARIOUS TEST EQUIPMENTHP5345A Counter TimerHP3400A RMS VoltmeterHP5326A Counter TimerHP5370A Counter Tinier 100MHzFluke 895A Differential VoltmeterMarconi TF2162 Attenuator

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WINCHESTER DRIVES 51/4"1.2J3 I uMb Full Freight ST506 (New> LI50£400 CORVUS 10MB/M for Apple £220

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DAISY PRINTERSDiablo 630R0 SerialDiablo 630R0 Sheet FeederOlympia ESW3000 ParallelTEC Starwriter F10/40 (New) 12BitOlivetti PR430 Serial




MATRIX PRINTERSTexas Silent 700 Serial 80 Col C125Texas Silent 800 Serial 132 Col C350Dec LA36 KSR Serial 132 Col £120Dec LA36 with Datosouth Board £l75Memorex 2073 Serial 80 Col £110A.1650 Ink Jet £120


HP722IC, HPIB, 8Pen A3 £875HP9872C £575HP9872S with Feed 8 Cutter C720Colcomp 1012 Serial 4 Pen L120

VDU'sTelevideo 925 £160Televideo 950 £220Pericom 7800 C125Pericom 6803 E125HP2624 with Thermal Printer £275HP2621 E150HP2647A Graphics Terminal £350

OPSU'sGould MGI2-10 Switch Mode £25Gould MG24-5 Switch Mode £25Gould Triple Output 15VI IA,

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FROMCHANNEL MICRO PRODUCTS LTD Maximum circuit board size greater than 2' x 2'. Powerful zoom facility and fast screen re -draw. Full on -screen editing. Mouse & Trackball compatible. Hard copy at 1:1, 2:1 & 4:1 from Epson F X or RX Plotter drivers for most popular plotters available. Low cost BBC Micro hardware keeps system cost below £1500.

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& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (89)

Multimeter includestransistor andfrequency tests

testing and frequencymeasurement ranges are the lesscommon additional functions on anew multimeter. The Metex M3650offers a large I.c.d. with auto -zeroand a 30 -position range selectionswitch. The meter offers f.s.d.measurements of voltage up to 751)V.alternating: 1000V. direct: 20A director alternating current, resistancefrom 200 to 20%1 capacitancefrom 200pF to 20pLF and frequenciesup to 200kIlz. Crotech InstumentsLtd. 2 Stephenson Road. St. Ives.I Iuntingdon. Camhs. PE174WJ. Tel:0480 30181.

Two processors inoneArguments between engineers overwhether to use 6502 or 780 expertisein company projects are resolved atonce with Rockwell's dual processorchip. More seriously. the dualarchitecture c.p.u. combines the fasti/o handling of the 6502 architecturewith the versatile Hock moveinstructions of the Z8(1 onto onechip. the two processorscommunicating through tri-portram at locations 0020 on the 6502and FE00 on the 7.80. This ram is

accessible externally to allowmultiple dual c.p.us to he connectedtogether: bus contention arbitrationis executed with an algorithm thataccesses the tri-port ram to readpreset device numbers. To keep thenumber Of pins down the data bus ismultiplexed with the lower eight hitsof the address bus. leading to 32 pinsfor each c.p.u. rather than the moreusual 40. and the two-sided structurerequires an upper and a lower p.c.h.Rockwell's specialist single -chipdistributor is RCS Microsystems Ltd141 Uxbridge Road. Hampton Hill.Middx TW12 1BL. Tel: 01-9792294.

Sealed rechargeablebatteriesEight batteries have been added tothe Power -sonic range of sealed lead -acid batteries. The new versionsrange from an 80Ah 12V model downto a 500mAh 6V battery which is only58mm long.

The advantages of these batteriesis that they need no topping -up andcan he used in any position. Theyoffer leak -proof cases. suspendedelectrolyte. overcharge protection.cycle or float applications. highdischarge rate and extended shelflife. Power -Sonic Europe Ltd.Cornwallis I louse. !Inward Chase.Basildon. Essex SS14 31313. Tel: 0268293353.

Soft -centred controllerLatest in a series of innovativeproducts from Dallas Semiconductoris what they call a softmicrocontroller. Superficially theDS50110 resembles a c-mos 8051, hutthe package also contains an 8K or32K-hyte static ram 164K ispromised) and a ten-year lithiumbattery. These and some tricks builtinto the processor make the unitproof against power failure, whetherfor a few instants or for much longer.When the supply is restored theprocessor simply resumes executionfrom where is left off. with all dataand registers intact -a feature whichalso makes the device very suitable

for use in portable data gathering.Software updates can he

downloaded to the DS5000 fromremote sources, over the telephone ifneed he. The built-in memory can hepartitioned dynamically intoprogram and data areas by the user.

In addition, a software protectionfeature makes it possible to save andload programs in encrypted form. Ifan unauthorized user tries to resetthe lock hit. the 40 -hit keyword isautomatically erased.

Initial 1000 -off price of the12MI lz. 32K -byte version is $80.Details from Joseph Electronics inBirmingham on 021/64:16888.


Make life easierand save moneyat the same timeby accepting our

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& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (90)

low- cost logic analysisToday's digital circuitry can't be debugged with just a logic probe andoscilloscope. A logic analyser has become an essential tool.The Thurlby LA160 system puts logic analysis within the reach of everyengineer with a wide range of options to suit many different applications.

Prices from £395 plus vat16 or 32 data channels

IBM-PC interface options

Data pods for random logicPersonality modules for uPs

Microprocessor disassemblers

No other logic analyser system approaches the value for money of theThurlhy 1.A160. Contact us now for full technical data.

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designed and built in Britain PE17 4BG, England. Tel: (0480) 63570


Hitachi Oscilloscopes leading the way from C320in performance and pricing! +VAT

The highest yeah-)The Hitachi nam: is synonymous with quality and reliability andis hacked by a 2 s 2ar or 3 year warranty on every oscilloscope.The keenest pricing

ith prices startng at only. (320 for a 20N1H/ dual -trace modelHitachi's price -pt rformance ratio can not he bettered..1 he largest rangeNos% totalling If: models the Hitachi range covers bandwidthsfrom 20MH, to I 50M11/ and digital storage models to 60MH/.'The fastest set -s ice

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EM S Power Systems

EMS manufactures DC Power Supplies andBattery Chargers both linear and switch modein a range from 5 VA to 3.2 KVA.Also a complete range of Standby, UPS andMains Stabilizer Systems 35 VA to 1 KVA. EMSspecialises in the manufacture of customisedproducts and has a full design anddevelopment facility.

EMS (Manufacturing) Limited,Chairborough Road,High Wycombe,Bucks HP12 3HH.Tel: (0494) 448484

Happy MemoriesPart type 1 off 25-99 100 up4164 150ns Not Texas 1.05 .95 .9041256 150ns 2.45 2.20 2.1041256 120ns 2.59 2.35 2.2541464 12Ons 3.35 2.99 2.792114 200ns Low Power 1.75 1.60 1.556116 150ns Low Power 1.40 1.25 1.206264 150ns Low Power 2.40 2.15 2.0562256 12Ons Low Power 8.75 8.50 8.252716 450ns 5 volt 2.95 2.85 2.802532 450ns 5.40 4.85 4.502732 450ns 2.60 2.40 2.252732A 250ns 3.30 2.85 2.752764 250ns Suit BBC 2.65 2.50 2.4027128 250ns Suit BBC 2.95 2.75 2.6527256 250ns 3.45 3.25 3.1027512 250ns 7.45 7.25 6.70Low profile IC sockets: Pins 8 14 16 18 20 24 28 40

Pence 5 9 10 11 12 15 17 24

Please ask for quote on higher quantities or items not shown.Data free on memories purchased, enquire cost for other.

Write or 'phone for list of other items including our 74LS seriesand a DISCOUNT ORDER FORM.

Please add 50p post & packing to orders under £15 andVAT to total. Access orders by 'phone or mail welcome.

Non -Military Government & Educational orderswelcome for minimum invoice value of £15 net.


Herefordshire HR5 3BR.Tel: (054 422) 618

(No stamp required)





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The 3132 solves three requirements atone go. 1) 20MHz; 2 mV/div Dual TraceScope. 2) Triple DC P.S.U. + 5V; ± 12V(Floating common). 3) ComponentComparator, for comparing active andpassive compolents.

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Heard a,out RWC LTD yet? Looking for someone who speaksyour language? When it's radio we have something for everyone!

e supply Companies and Government Departments Worldwidewith Communications related systems and equipment. Some ofour specialities include: All mode Scanning Receivers and antennas 25 MHz - 2 GHz. Achoice of model and option modified by RWC to suit your exacting needsand requirements Custom designed Communication systems. UK MPT TypeApproved equipment designed to meet your requirements. includingBroadcast industry talkback systems. Handhelds. UHF/VHF repeatersystems. Marine Radio. HF point to point links, Radiotelephones andCellular telephones

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UK made Raycom Cost Effective Regulated 13.8 Volt powersupplies. A choice of units 3A to 12A with metered options

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FOR THE BEST CIRCUITSIMULATION C.A.D.Designers are turning to 'THOSE ENGINEERS' software. They keep aheadby knowing what is going on while free to experiment without the costs.delays and uncertainties of physical testing. Those Engineers softwarewhich creates a net list removes the chores and errors in documenting.Ask us too for schematic layout software.


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timing diagrams plotted.DC transfer curves plotted.Bode curves (gain and phase) plotted.also phase delay output.transients output in frequency domainMonte Carlo and Worst Case.Components temperature effectssupportedBreakpoints and polynominals supportedI - lo* (expffv'q)/(n'k't)) -Resistors may have inductance etc. etc.Component characteristics can be made tovary with both time and frequencyaccording to any function. Offset currentsmay be imposed.Up to 64 connections per model to maincircuit, no limit on number or size.Signals may be sampled or injectedanywhere.Interactive mode has powerful editing andinterrupting facilities Batch mode forheavy work allows you to come back.Sparse matrix technique allows typicallyover 500 modes in 5I2K memory. 8087 (or80287) coprocessors supported.A ring -bound reference manual of over 200pages is an integral part of ECA-2.If you need more convincing, ring us fordetails of money -back trialECA-2 costs lust 1695 k VAT. ECA-2compares favourably with well-knownmainframe simulators and is more powerfulthan any other we know available on PCs

THOSE ENGINEERS software which is available from C99 supports IBM PC s andompatibles and the range of BBC microcomputers. As engineers in electronic and

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& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (92)

I0 BROADCASTDigits-not

without tearsDigital audio is rapidly infiltrat-ing into both radio and televisionbroadcasting, although not with-out experiencing difficulties sel-dom foreseen by the early advo-cates of "rugged go/no-go,hands-off operation." Indeed, itis the abrupt change from go tono-go, that replaces the more -certain but more -gradual de-gradation of analogue signals,that is tending to cause unex-pected headaches for transmis-sion engineers. British Telecomengineers have reported en-countering unexpectedly severeproblems during the rare occa-sions when multipathtropospheric -propagation condi-tions exist right down to thelevels of microwave towers.

In an ICAP87 paper, M.C.D.Maddocks and J.H. Stott of BBCResearch describe problems ex-perienced on a new digital u.h.f.link between Stockland Hill,Devon and Alderney intended tocarry a multiplex of radio prog-rammes from the UK to theChannel Islands radio transmit-ters, replacing existing analoguelinks. This was designed to pro-vide reliable, high -quality audio,despite there being at least a50dB fading range on this long,over -the -horizon sea path. Pro-pagation data were availablefrom the existing analogue tele-vision links over this path, re-ceived on the IBA's adaptiveantenna and (for diversity) a

large parabolic dish reflectorantenna.

Predictions suggested thatsignal-to-noise values should besufficient for the digital link to beopen for 99.85 per cent of thetime, free of objectionable co -channel interference 99.7 percent of the time, indicating atotal predicted performance of99.55 per cent of time and a linkoperational time of 99.4 per cent.In practice, measurements onthe experimental link taken overseveral months indicated a linkoperational time of 97.8 per centwith 89.5 per cent error -freeseconds.

The BBC engineers noted thatalthough the majority of linkfailures lasted less than tenseconds, there were a significantnumber of longer failures, sub-jectively more damaging and in-

creasing in frequency in earlyafternoon and late -night periods,both recognised as importantradio broadcasting times. Thelink failures also posed the prob-lem that they were neither soshort as to be disguised in thesignal decoding, for example bymuting, nor so long as to be veryrare. While it is hoped to identifythe reasons for the unexpectedlypoor performance of the ex-perimental link, it seems likelythat a considerably more com-plex digital modem may provenecessary. No doubt all will comeright in the end but it is anotherindication that digital transmis-sion can throw up new problems.


Some years ago the BBC con-ducted a programme of ex-perimental terrestrial broadcast-ing of digital signals using theBand 1 v.h.f. transmitter at Pon -top Pike. Although this wasfound to provide excellent quali-ty reception at most, though notall. domestic locations, portableand mobile reception proved ex-tremely dicey owing to the des-tructive effects of short-termmultipath propagation -a condi-tion that can still cause digitalteletext to display "garbage"(error -prone) pages in someurban standing -wave situations.But teletext is not expected tohave to cope often with the se-vere multipath of mobile recep-tion.

Although both the BBC andIBA are planning to use digitalstereo (plus the conventionalanalogue channel) for televisionsound in the fairly near future,direct transmission of signals indigital form for terrestrial radiobroadcasting in the UK seems tohave been put on the back -burner for the time being.

However, according to theRussian engineer F.I. Vlasov in a1986 article in the OIRT journalRadio and Television. an ex-perimental digital sound broad-casting system was established in1983 in Leningrad. and then in1985 in both Leningrad and Tal-lin using the "newly available"frequency of 102.656 -MHz (untilrecently East European v.h.f.broadcasting has tended to usefrequencies around 70 MHz). No

details are given of the resultsachieved and the extent of anymultipath problems but it is sug-gested that while the band 100 to108 MHz would be suitable foronly three analogue stereo net-works. six stereo digital pro-grammes could be accommo-dated as a multiplex within a4 -MHz band, provided that alltransmitters used the same car-rier frequency and each soundsignal (mono or one of a stereo -pair) is coded in a floating-pointcode with 10 -bit mantissa and3 -level codes. With a samplingfrequency of 32 kHz, the bit -ratewould be 4.096 Mbit/s with dou-ble phase -shift modulation.

F.I. Vlasov concludes that "atthe present time we are partici-pating in a revolutionary processof a radical change in soundbroadcasting technology. Digitalsound engineering is the tech-nology of the 21st century: in ourdays it is making its first stepsand conquering ever new fields."

It is clear from this paper thatthe Russian engineers are care-fully following developments indigital audio engineering outsideof the USSR. F.I. Vlasov regretsthat standardization of encodingparameters has not beenachieved with 48 kHz samplingused in digital studios. 44.1 kHzfor laser (CD) sound, and 32 kHzfor transmission links, with re-peated rate -conversions increas-ing costs and, unless adequatemeasures are taken, reducingthe quality of programme sound.Bit numbers and coding lawsalso differ: 16 bit linear codinghas been standardized for CD.but 14 bit linear and 10 and 9.5bit non-linear codes are used ontransmission channels. Everyattempt, he believes, should bemade to avoid increasing stillfurther the divergence betweencoding parameters.

He notes that CD records havecreated a need for improved re-production systems and lists assuitable for monitoring purposesanalogue loudspeakers havingabout 110 dB dynamic range andcapable of maximum soundpressure levels of about 128 dB.in which category he puts theTechnics B-10. Mitsubishi DS -505 and Junior (Kreisler) louds-peakers, adding "The monitorunits of the English firms Tan-noy (M-1000 and M-3000 units)and Bowers & Wilkins (B&W-801and B&W-868) also approach

meeting the requirements ofdigital."

But he also looks beyond theanalogue systems, noting thatBell Laboratories have developeda system for immediate conver-sion of a digital signal with thedecoding effected directly on thediaphragm. As a third possibilityhe notes the potential of adaptivesystems such as that demons-trated by Acoustical Research in1982 which includes adaptationto the acoustic characteristics ofthe listening room by the use ofmicroprocessors, adding "In ouropinion the development ofadaptive sound reproduction sys-tems constitutes the main trendof development in the near fu-ture, as it will be possible tocreate sound reproduction sys-tems satisfying all requirementsof the prospective digital soundchannel."


The use of digital data carried onsub -carriers of v.h.f. broadcaststations seems likely to increasein the near future. Telerate (UK)Ltd have now launched theirsubscriber radio teletext serviceon the 97.3 MHz LBC channel inLondon, with the similar Tele-met system on the Capital trans-mitter due later this year. TheBBC has launched full test trans-missions of the EBU Radio DataService (RDS) in preparation foran official launch of the systemin September. providing auto-matic location of the strongestsignal. display of station name.alternative frequencies of a givenservice, time and date. This ser-vice is due to be available from allBBC v.h.f. transmitters in Eng-land by the autumn, and RDSmay also soon be available on IBAtransmitters. The successful in-troduction depends to a markedextent upon the willingness ofsemiconductor manufacturersto develop special purpose I.s.i.chips. with the usual chicken -and -egg quandary of firms beingreluctant to incur heavy develop-ment costs until they have someevidence of a market demand:while broadcasters find it diffi-cult to start a new service untilreceivers are available.

Radio Broadcast is written by PatHawker.


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (93)


moveWhile the Royal Signals are stillstriving to come to terms withorganizational and managementrequirements for the Ptarmigantactical Cil line and radio battle-field communications system, ateam at the Royal Signals &Radar Establishment at Malvernhas been busy investigating thepossibility of introducing store -and -forward digital packet -switching technology into com-bat net radio systems operatingon a single narrow -band chan-nel. Following the use of a smallnumber of experimental units,the team intends to expand itswork with the acquisition bycommercial procurement of anexperimental 25 station unit.With this, it is planned to developand further refine the distributedalgorithms so far developedbased on the need for the packetswitching to operate effectivelyin a highly mobile and hostileenvironment.

The current RSRE work isdescribed by B.H. and T.R.Davies in some detail in an in-vited paper in a special issue(January, 1987) of Proc. IEEE.This issue devotes over 150 pagesto the use of packet -switchingtechnology for mobile -radio net-works, mostly for military -typeapplications. The guest editorsapologize for the preponderanceof military -sponsored papers, ex-plaining "This is due to the un-fortunate lack of success that weexperienced in including a paperon the application of this tech-nology to the commerical andamateur sectors. This absence.however, should not underminethe importance of these areas ofapplications. In fact, some com-mercial systems are in use. in-cluding communications to fieldengineers and support of pack-age delivery services."

Meanwhile, the UK Royal Sig-nals officers are still seeking tolearn from early field experienceof Ptarmigan and its radio -relaysector, Treffid, following its rolein the 1986 "Exercise SummerSales" in West Germany. whichwitnessed the first large-scaleuse of Ptarmigan at Corps level.

It is recognised that the RoyalSignals faces the challenge ofmanaging an area system super-imposed on a hierarchical corn-

mand structure, a friction -provoking situation that is notproving easy to solve. Major G.R.Leach has written (J. Royal Sig-nals Institution) "successful de-ployment of Ptarmigan relies ona close understanding of the dif-ference between command of thetrunk system and its electronicmanagements." He stresses thatthe success of Ptarmigan is re-liant on good -quality radio -relaylinks and that the burden ofproviding these depends on theability of junior commanders,including the radio -relay detach-ment commanders, the Reccesergeants and the trunk -networkcommanders. Differences ofopinion between these on suchmatters as the siting of the radio -relay units can jeopardize theeffective operation of a wholePtarmigan battlefield system.

Such large-scale military exer-cises are having increasingly torecognise that Warsaw Pactforces have developed a sophisti-cated concept of offensive elec-tronic warfare (radio electroniccombat support) and would cer-tainly attempt to intercept, ex-ploit and disrupt the com-munications of their enemy.


The recent marked upsurge ofR&D interest in superconductiv-ity has followed the discovery,initially by Bednorz and Miller ofIBM Zurich but now apparentlywith Japanese scientists in thelead. of a completely new familyof "high -temperature" oxide -ceramic superconductors andseen by some observers as "aninvention comparable to that ofthe transistor." For the com-munications engineers, it raisesthe possibility of improved low -noise devices for microwave,millimetre -wave and opticalcommunications. The way seemsopen for improved diode detec-tors and mixers by means ofsuper -Schottky diodes withjunctions having a hybridsuperconductor/semiconductorstructure used with the relativelyinexpensive liquid nitrogencoolant.

Superconductivity. first dis-covered by the Dutch physicistHeike Kamerlingh-Onnes in1911. is the curious property of

many electrical conductors tochange abruptly to a state of nomeasurable resistance whentheir temperature closelyapproaches absolute zero (OK.-273°C). It was not until 1957that a comprehensive theory ofsuperconductivity was formu-lated by J. Bardeen, L.N. Cooperand J.R. Schrieffer (the "BCS"theory). This led to a graduallyincreasing exploitation, or atleast investigations into themany potential applications inthe 1960s, including the con-firmation of some aspects of the"Josephson effect" predicted byBrian Josephson in 1962 andwhich is seen as providing thekey to the application of super-conductivity for super -fast com-puters as well as for low -noiseelectronics.

Most of the R&D on theJosephson effect has been target-ted on the development of com-puters. with IBM concentratingon its use as a switching device(though reportedly largely aban-doning this project a few yearsago) and Bell Laboratories seek-ing ways of using Josephsonjunctions to increase the speedand capacity of central computermemories.

But until the recent ceramic -oxide breakthrough, supercon-ductivity could only he achievedwith the use of costly ('.quidhelium (boiling point 4K) as thecoolant. With the transition to asuperconductive state of barium -yttrium -copper oxide found byMitsubishi scientists to be over90K, the much cheaper andeasier to handle liquid nitrogen(boiling point 77K) can be usedas the coolant.

It could, however, be low -noise communications that maybenefit before computers.Temperature of the coolant is

not the only problem in usingJosephson -junction devices incomputers. It has yet to beshown that it is possible to com-bine large numbers of such de-vices on to a single chip, becauseof the tendency for different sta-bility problems to be found ineach junction. This, however.would not necessarily preventtheir use as discrete devices inlow -noise applications. NEChave reported the developmentof a functioning Josephson de-vice based on two layers ofsingle-phase yttr um -bariumcopper oxide.

It may be recalled that theoriginal low -noise receiver atCoonhilly Downs in the early1960s was based on a helium -cooled maser having extremelylow -noise parameters but, apartfrom expense, this proved tohave too narrow a bandwidth forthe later generations of com-munications satellites.

ICAP87Among the near -950 pages of the(EE's two-part Conference BookNo 274 covering the recent In-ternational Conference onAntennas and Propagation(ICAP87) at Sheffield Universityare no less than 179 papers and47 poster presentations - for-midable tomes indeed. However,they include not only the usualesoteric and highly mathematic-al analyses favoured by special-ists in these fields but also quite anumber of more down-to-earth(if that is the appropriate ex-pression) and practical papers.These range from interestinghistorical surveys of 100 years(dating from Heinrich Hertz) ofantenna development and pro-pagation research to practicalengineering papers on the designof microwave towers with emph-asis on wind hazards. The BBChas also come up with somelessons from the past, includingexplanations of how they tackledsuch unexpected problems as thePenge effect. "ghosts" in Pre-ston. hazard -lamp hazards andthe rusty -bolt effect that can giverise to spurious inter -modulation products. It is alsointeresting to note that MarconiResearch have been doing newdesign work on the 50 -year -plusBruce rhombic antenna relatingbandwidth to apex angle. Recep-tion of v.h.f. signals in urbanareas, including an improvedSwedish model for hilly wood-land from which it seems that aforest may theorectically be tre-ated as a dissipative. lossy dielec-tric slab lying on a half -spaceground. There is also an illumi-nating paper on height -gain atv.h.f. in urban, rural and over -sea paths. The computer hasmade possible the use of the"Method of Moment" techniqueto predict antenna performance.

Radio Communications is writ-ten M' Pat Harker.


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COMPONENTSTheir compact size and low magnetic

interference make Nuvotem's toroidal transformersideal for today's types of power supply and powerrequirements in a wide variety of electronicapplications. The benefits are clear: Significant savings in weight and volume overconventional transformers. Competitive price. No air gaps - hum almost completely eliminated. Nuvotem design and advisory service -customised components for specific applications. Highest standards of quality assurance - 100°/0tested. Also available - a standard range - 15VA-500VAplus a range of filter chokes.

GET TOME CORE OF THINGS -for further information complete and return the couponor telephone Nuvotem today.=NEM, 41/M ILM7


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'Exclusive of V.A.T. and Post and Package'50 50 1. 50

74LS00 013 0 10 6821 1 40 1 00 2764-25 2 40 2.2074LSO4 0 13 010 6502 330 280 27128-25 3.50 3 4074LS08 0 13 0 10 6522 330 2 80 27256-25 390 3 7074LS21 0 15 0 12 65CO2 700 600 6116LP-3 1 50 1 4074LS37 0 13 0 10 6809P 3 20 285 6264LP-15 200 1 8574LS74 0.13 0.10 745138 0.30 0 25 62256-12 11 00 9.5074LS86 0.13 0 10 74S240 0 40 0 35 4164-15 1 00 aso74LS122 020 0 18 8085A 1 40 1.20 41256-15 240 22074LS244 040 0.32 8255-5 1.80 1 65 Z8OACPU 140 1 0074LS245 0.44 032 4 meg Crystal 030 0 25 280ACTC 1 40 1 CO74LS367 0 23 017 LM324 0 25 020 ZEIOAP10 1 40 1 1074LS373 0 40 030 LM339 0.25 020 8253 1 40 1 2574LS374 0 40 0.34 LM386 050 042 6845 1 90 1 3074LS399 0 30 020 LM556 035 025

All memory prices are fluctuating daily please phone to confirm prices.

178 Brighton Road,Purley, Surrey CR2 4HATel: 01-668 7522


Editorial Feature ListAUGUST 1987Short -haul optical -fibre data communica-tions is an essential part of modern communica-tions systems This feature presents an overviewof the techniques employed and the hardwareavailable.SEPTEMBER 1987Microwave semiconductor devices. Thesespecialised components retain an air of mysteryfor many engineers. We present a feature on thephysics of these devices and characterize thetypes now is use.For further advertising details please ringMartin Perry on: 661 3130 or Michael Downing on 661 8640


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (95)


proliferateAt the height of the PAL \ TSC/SECAM controversy in the1960s, at least one large orga-nization issued a firm edict thatit* engineers should not attemptto develop any new colour -encoding systems, but insteadshould concentrate on solvingthe problems of one of the threeproposed systems which wereshowing an alarming tendencyto proliferate new versions.Judging by the number of sys-tems now emerging in the fieldof direct -broadcasting fromsatellite and for wide-screenh.d.tv. perhaps it is time that asimilar ban should be imposed.The basic problem is to decidewhether "compatibility" with ex-isting standards is or is not anessential requirement for possi-ble world standards.

There is at least still time forconsideration, with Americanbroadcasters at the momentmore concerned with financialthan engineering aspects of fu-ture television, partly resultingfrom the financial difficultiesthat have followed companytake-overs or from fighting offsuch take-overs. in which theprocess of issuing "junk bonds"seems to have led to over-capitalization and sparked off adrastic round of cost-cutting. Yetthe increasing practice of usingelectronic production ratherthan film for some of the majorAmerican drama series and sub-sequent up -conversion to 625lines does underline the need foran improved electronic produc-tion standard, whether or notthis is the 1125 -line 60Hz stan-dard that has been opposed byEuropean broadcasters.(although German broadcasters.but not the German Bundespost,have committed themselves tosupport of 1125 as a productionstandard).

William Dobbie of BritishTelecom Research is proposing anew MAC system, designed foroptimum bandwidth efficiency.which would allow two program-mes of conventional quality to betransmitted in a single DBSchannel, or alternatively wouldprovide options for a single wide-screen h.d.tv transmission. Inthe USA, Faroudja Laboratorieshave developed a technique for

improving the images of 525 -lineNTSC. Dr William Glenn is advo-cating an h.d.tv system compati-ble with NTSC which could betransmitted with the aid of anextra 3MHz channel on terrest-rial networks. Richard Iredale(Del Ray Group) has a proposedHD-NTSC system that would befully compatible, depends on a"TriScan" concept of smart scan-ning combined with digital pro-cessing in the receiver and wouldpermit a change of aspect ratio to14:9. Europe is still divided be-tween support for the MAC varia-tions including B -MAC. C -MAC.D -MAC (Eu-MAC ), D2 -MAC etc..with subsequent "evolutionary"progress to wide-screen h.d.tv.


1986 was a boom year for theHigh Street consumer -electronics shops, with no lessthan 3.9 million colour televi-sion sets reaching the retailersand rental chains: with video-cassette recorders recovering tothe 2 million levels achieved afew years ago: and with CD re-cord players up fourfold on 1985to almost 640,000 units deli-vered to the trade. With so manymajor Japanese firms now hav-ing UK factories it is also notsurprising that exports of theso-called "brown goods" are alsorunning at record figures.

But the retail trade is far fromhappy. claiming that profit mar-gins are far too low. Lord Chap -pie, chairman of BREMA. claims"I find it depressing that such anefficient and dynamic industryfinds it impossible to hold pricesat sensible levels which wouldallow reasonable margins to allinvolved." This reflects the rowthat broke out following anannouncement earlier this yearthat some manufacturers werebeginning to cut the £50 -or -soprice differential between setsfitted with the flatter, squarerpicture tubes. now amounting toabout 70 per cent of the produc-tion of large -screen sets. andthose with conventionallyshaped picture tubes.

The BREMA chairman be-lieves that technological innova-tion should be used to induce thepublic to pay "more reasonable"prices. quoting the example of

teletext. Yet my recollection ofthe early struggle to establishteletext as a viable operation isthat it nearly died the death ofpublic apathy until the Depart-ment of Trade & Industry step-ped in, appointed R:c Foot topromote the system energetical-ly and induce the Treasury tomake, at least temporarily,financial concessions that en-abled rental firms to charge vir-tually the same rentals as forremote -controlled sets not fittedwith teletext decoders.

Then again, BSB. in planningto begin direct broadcastingfrom satellite by 1980, havewidely publicized the figure of£200 as the likely "initial" cost ofa suitable dish antenna plus theindoor unit including the MACdecoder, a decidedly optimisticfigure that would not give muchscope for "sensible margins".especially if the public came toexpect that this would includeinstallation costs.

Apart from the controversialdigital audio recorders (DAT)which may finally appear in HighStreet shops later this year.another potential market thathas yet to be developed is forconsumer -priced electronic"stills" cameras. Casio haveannounced that they hope tolaunch the first such cameraintended specifically for the con-sumer in the North Americanmarket very shortly. This camerauses the standard 2 -in video -floppy as standardized for profes-sional cameras. This can hold upto 25 full frames or 50 fields ofcolour pictures. The Casiocamera has an m.o.s. image sen-sor capable of 280.000 -pixel re-solution, shutter speeds fromone -eighth to one -thousandth ofa second and the ability to takefive fields continuously in onesecond. The camera will includethe facility to playback on anytelevision set 1525 -line models)without the need for a separateplayer unit.

The price in Japan is Tinder£500.

Puzzles remainThe publication last November.coinciding with the many 50 -year anniversary events, of the500 -page hook British Television- The Formative Years. by Pro-fessor R.W. Burns - was clearly

intended, and seems likely toremain, the definitive study ofBritish television from the firstBaird experiments in 1923 to theconfirmation of the Marconi -EMI 405 -line system as the UKstandard for Alexandra Palace inFebruary 1937. It covers in con-siderable detail the 1926 to 1934struggle by Baird to make 30 -linetelevision broadcasting the basisof a viable industry, against thewell-founded opposition of theBBC. At first the BBC were sup-ported in opposing Baird by thePost Office engineers, who alsoformed the executive side of theregulatory body. But then, fol-lowing the success of Baird inobtaining political support andthe belief of the Post Office'slegal advisors that the then Wire-less Telegraphy Acts did not cov-er the transmission of visualimages, the Post Office attitudebecame increasingly ambivalentand in the end they virtuallyforced the BBC, albeit reluctant-ly, to agree to provide transmit-ters for experimental 30 -linetransmissions.

Professor Burns has drawnwidely, although at times ratherselectively. upon the BBC andPost Office archives. But I won-der if I am alone in feeling that hehas left a few important ques-tions unaswered.

For example, how did Profes-sor E. Taylor Jones come to writesuch an extraordinarily favour-able report in the highly re-spected journal Nature (18 June.1927) of the crude London/Glasgow land -line demonstra-tions, writing "The image wasperfectly steady in position, wasremarkably free from distortionand showed no sign of thestreakiness which was. I believe,in evidence in the earlier ex-periments...My impression afterwitnessing these demonstrationsis that the chief difficulties con-nected with television have beenovercome by Mr Baird and thatthe improvements still to beeffected are mainly matters ofdetail." It is extremely difficult tobelieve that this support fairlyrepresented genuine resultsachieved in these hurriedly setup 1927 demonstrations. WasProfessor Jones fooled? And if sowho was responsible for "rig-ging" the demonstration?

Television Broadcast is writtenby Pat Hawker.


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (96)

01-208 1177 rh( 1-INOMA VIC L D 01-208 1177BBC Computer & Econet Referral Centre

AME115 BBC MASTER1 tree software £385 fa) AMB12 BBC MASTER Econet 0299 (a)AMCO6 Turbo (65C - 021 E xpansion Module 199(b)ADC06 512 Processor 1195(b) ADJ24 Advanced Ret Manual C113(c)ADF14 Rom Caendge £12.75 (b) ADJ23 Ref Manual Part II £14 fa)ADJ22 Ref Manual Part 1 C14 (e) BBC Master Dust Cover C4.75 (d)

BBC MASTER COMPACTFree bundled software within priceSYSTEM I 128K Single 640K Once and bundled software £385 (a)SYSTEM 2 System 1 with a 12 Hi Res RGB Monitor E469 (a)SYSTEM 3 ystem 1 with a 14 Med Res RGB Monitor £599 fa)Second 3 5 Drive Ka C99 (c) Extension Cable for ext 5 25 drive C10 (d)

View 3.0 User Guide C10 (d)BBC Dust Cover C4.5008ADFS ROM (for 13 with 1770 DFS 5 B Plus C26 (d)ACORN 280 2nd Processors C329 (a)MULTIFORM Z80 2nd Processor £269 (b)TORCH Z80 2nd Processor ZEP 100TZDP 240 ZEP 100 with Technomatic PD800P dual drive with built-i

Viewsheet User Guide C10 (d)1770 DFS Upgrade for Model B C43 (41)

1 20S ROM EIS (d)Universal 2nd Processor Adaptor C75 (b)

ACORN IEEE interlace 1265 (a)C229 (a)

n monitor stand £439 (a)

META Version III - The only package available in the micro market that willassemble 27 different processors at the price offered. Supplied on two 16Kroms and two discs and fully compatible with all BBC models. Please phonefor comprehensive leaflet £145 (b).

We stock the full range of ACORN hardware and firmware and a very wide range of otherperipherals for the BBC For detailed specifications and pricing please send for our leaflet

DISC5.25" Single Drives 40/50 switchable:

DRIVESTS400 400K/640K £114 (b)PS400 400K/640K with integral mains power supply £129 (b)5.25" Dual Drives 40/80 switchable:TD800 800101208K £226(a)PD800 800/K1280K with integral mains powr supply £229 (a)PD800P 800K/1280K with integral mains power supply and monitor stand £249 (a)3.5" 80T DS Drives:TS351 Single 400K/640K 175 (b)PS351 Single 400K/640K with integral mains power supply £95 (b)TD352 Dual 800K/1280K f135 (b)P0352 Dual 800K/' 280K with integral mains power supply 1152 (b)PD853 Combo Dual 5.25'73.5" drive with p.s.0 £229 (a)

EPSONEPSONFX800FX1000EX800EX 1000L0800 (80 col)L01000L02500

PRINTERS & PLOTTERSSTAR Nl_10 (Parallel Interface) £229 (a)

BROTHER HR20 £349 (a)

COLOUR PRINTERSIntegrex Jet Printer 1549 (a)

Dotprint Plus NLO Rom forTAXAN Epson versions for FX, RX. MXKP815 (160 cps) £249 (a) and GLP £28 (d)

£329 (a)£449 (a)£409 (a)£595 (a)£439 (a)£609 (a)£795 (a)

KP915 (180 cps) 1379(a)

JUKI6100 (Daisy Wheel)

PLOTTERsh*tachi 672 1479 (a)Graphics Workstation

(A3 Plotter) 1599 (a)NATIONAL PANASONIC Plotmate A4S £375 (a)KX P 1081 (80 col) 1169 (a) Plotmate A4SM £455 (a)KX P 3131 (38K butter) £249 (a) Plotmate A3 £425 (a)KX P 3132 (32K butler) £249 (a) Plotmate A3M £574 (a)

£310 (a)

3M FLOPPY DISCSIndustry Standard floppy discs with a lifetime guarantee. Discs in packs of 10

51/4" Discs 31/2" Discs40 T SS DD 110.00(d) 40 T DS DD 111.50(`d) 80 T DS DD £18.0080 T SS DD 114.00 (d) 80 T DS OD 115.00 (d) 80 T DS DD £23.00

FLOPPICLENE DRIVEHEAD CLEANING KITFLOPPICLENE Disc Head Cleaning Kit with 28 disposable cleaning discsensures continued optimum performance of the drives. 5' 4" £12.50 (d)

3' 2" £14.00 (d)

DRIVE ACCESSORIESSingle Disc Cable E6 (d) Dual Disc Cable £8.50 (d)10 Disc Library Case £1.80 (d) 30 x 5' :2 Disc Storage Box E6 (c)50 x 512 Disc Lockable Box 09.00 (c) 1130 x 512' Disc Lockable Box E13 (c)

PRINTER ACCESSORIESWe hold a wide range of printer attachments (sheet feeders, tractor feeds etc)

i in stock. Serial, parallel, IEEE and other interfaces also available. Ribbonsavailable for all above plotters. Pens with a variety of tips and colours alsoavailable. Please phone for details and prices.Plain Fanfold Paper with extra fine perforation (Clean Edge):2000 sheets 9 5' x 11" 113(b) 2000 sheets 14.5' x 11' £18.50(b)Labels per 1000s Single Row 3:" x 1 7/16' 15.25(d) Triple Row 2-7/16' x 1 7/16" 15.00(d)

MONITORSRGB 14"1431 Std Res E179 (a)1451 Med Res 1225 (a)1441 Hi Res 1365 (a)MICROVITEC 14" RGB/PAL/Audio1431AP Std Res 1199 (a)1451AP Std Res £259 (a)All above monitors available in plastic ormetal case.MICROVITEC 2e2030CS RGB/PAL'Aucho £380 (a)2040CS RGB/PAL'Aduto £685 (a)TAXANK12SV 62012" 1279 (a)K12SV 62512" £319 (a)MITSUBISHIXG1404 14 Med Res RGB, IBM i3 BBCcompatible 1219 (a)

MONOCHROMETAXAS 12 HI-RESKX117 12 Green P31 185(aKX118 12" P39 £95(aKX119 12' Amber £90 (a

PHILIPS 12" HI-RESBM7502 green screen E75 (a)BM7522 amber screen 179 (a)

ACCESSORIESMicrovitec Swivel Base (DS4 only) E20 (C)Taxan Mono Swivel Base withcl°Ck£22 (c)Phipps Swivel Base £14 (c)BBC RGB Cable 15 (d)

13.50 (d)MicrovitecTaxan 15 (d) Monochrome 13.50 (d)Touchtec - 501 £219 (b)

MODEMSAll modems carry a full BT approval


WS4000 V21/V23 (Hayes Compatible.Intelligent, Auto Dial/Auto Answer) £149 (b)WS3000 V21/23 Professional As WS4000and with BELL standards and battery back upfor memory £265 (b)

WS3000 V22 Professional As WS300 V21/23but with 1200 baud full duplex 1445 (b)

WS3000 V22 Ws Professional As V22 and2400 baud full duplex £585 (a)The price of WS4000 and WS3000modems includes a COMMSTAR II ROMand BBC Data Cable.

WS2000 V21/V23 Manual Modem £92 (b)DATA Cable for WS series, PC or XT £10 (d)Auto Dial Card £27 (d)Auto Answer Card £27 (d)WS2000 SK I Kit £5 (d)

This offer can only apply if it is specified at thetime of placing your order for the modem.

RT256 3 PORT SWITCHOVERSERIAL INTERFACE3 input 1 output or 1 input -3 outputmanual channel selection Inputoutput baud rates. independentlyselectable 7 bit/13 bd. oddieven'nonepanty Hardware or softwarehandshake 256K butler. mainspowered 1375 (b)

PB BUFFERInternal butler for most Epsonprinters Easy to install Ins)suppliedPB128 128K 199(c)

UVERASERSuv1T Eraser with built.in timer and mains indicatorBuikin safety interlock to avoid accidental exposureto the harmful UV raysIt can handle up to 5 eproms at a time with an averageerasing time of about 20 mins £59 + E2 p&p.UV1 as above but without the timer E47 + £2 p&p.For Industrial Users. we offer UV140 6 UV141 era-sers with handling capacity of 14 eproms UVI41 hasa built in timer Both otter full built in safety featuresUV140 t69, UV141 p&p 12.50.


Mains powered convenersSerial to Parallel E48 (c)Parallel to Serial 148 (c)Bidirectional Convener 1105 (b)

Serial Test CableSerial Cable switchable al both endsallowing pin options to be re-routed orlinked at either end - making it possibleto produce almost any cableconfiguration on siteAvailable as M,M or MuF £24.75 (d)

Serial Mini Patch BoxAllows an easy method toreconfigure pin functionswithout rewiring the cableassay Jumpers can be usedand reused £22 (d)

Serial Mini TestMonitors RS232C and CCITTV24 Transmissions.indicating status with dualcolour LEDs on 7 mostsignificant lines. Connects inLine E22.50 (d)


I.D. CONNECTORS(Speedbaock Type)

No of Header Recep Edgeways Plug 'acre Conn

1 110p 1159 1209200 145p 125p 195926 1759 1500 240934 2009 160p 320p40 2209 1909 340p50 235p 200p 390p

SOFTY IIThis low cost inlell gent eprom programmer can program 2716 25162532 2732 and with an adaptor 2564 and 2764 Displays 512 bytepage on TV - has a serial and parallel I/O routines Can be used as an emulator cassette lilted aceSoftyii 1195.00(b)Adaptor for 27642564 C25.00

SPECIAL OFFER264-25 £3.20 (d);

27128-25 £3.50(d)27256 £5.50 (d);27512 £9.00 (d);

6264 LP -15 £2.80 (d).


9 15 25 37MALE:Ang Pins 120 180 230 350Solder 60 85 125 170IDC 175 275 325 -FEMALE:St Pm 100 140 210 380Ang Pins 160 210 275 440Solder 90 130 195 290IDC t95 325 375 -St Hood 90 95 100 120Screw . 130 150 175 -Lock


CONNECTORS2 6 -wan (commodore)2 10 -way2 x 12 way Ivor 2012x 18 way2 x 23 way 1288112x 25 way2 x 28 way iSpectiumt2x 36 wayI x 43 way2x 22 way2 x 43 way

x 77 way2 x 50 wayiSI00conn-

0 1 O156- 3150p


- 3409509- 1

1759 220p2259 220p2009 -2509 -2809 -90939594009 50096009


36 way plug Centronics(solder 500p CC) 475p36 way ski Centronics(solder) 550p (IDC l 500p24 way plug IEEE (solder)475p ( IDC 475p24 way ski IEEE solder)500p (IDC: 500pPCB Mtg Skt Ang Pin24 way 700p 36 way 750p

RIBBON CABLE,grey nwfrel

10 -way 40p 34 -way 160p16 -way 60p 40 -war 100p20 -war asp 50 -way 200p26 -way 1209 64-wai 2909

TEXTOOL ZIFSOCKETS 24 pin 67.6028.pin re 10 40 pin C12.10

EURO CONNECTORSDIN 41612 Plug Skt2 X 32 way St Pin 230p 275p2 x 32 way Ang Pin 275p 320p3 x 32 way St Pin 260p 300p3 x 32 way Anp Pin 375p 400pIDCSkIA+B 400pIDC Skt A + C 400p

For 2 x 32 way please specifyspacing (A + B. A + C;.


Male to MaleMale to FemaleFemale to Female


14 pin16 pin18 pin20 pin24 pin28 pin40 pin


40p 100p50p60p


75p100p 150- p

160p 200p200p 225p

RS 232 JUMPERS125 way Di

24 Jingle end Male24 Single end Female24 Female Female24 Male Male24 Male Female


01000C95009 50

MISC CONNS21 pin Scart Connector 200p8 pin Video Connector 200p

DIL SWITCHES4 -way 90p 6 -way 105p8 -way 120p 10 -way 150p

ATTENTIONAll prices in this double pageadvertisment are subject to

change without notice.ALL PRICES EXCLUDE VAT

Please add carriage 50punless indicated as follows:(a) £8 (b) 12.50 (c) 11.50 (d)


TECHNOLINE VIEWDATA SYSTEM. TEL: 01-450 9764 Using Prestel' type protocols. For informationand orders - 24 hour service, 7 days a week


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (97)

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& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (98)

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"SIN Parallel CaMmelcs CsavoMerIdeally suited for computers that can notsupport Parallel PrintersKit comprising: PCB. Components 36wayCentronics IDC Plug and Patch LeadKIT PRICE 17.95BUILT & TESTED 25.95Sinclair QL 'SERI or 2. Plug 1.4225W D' Type Plug or Socket 0.60Car ICE Warning IndicatorKIT PRICE 5.95BUILT 8 TESTED 8.95

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ASA Ltd.. Dept. Y. Brook House. Torrington Place. London WC I E 7H N.

This space is donated in the interests of high standards of advertising


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Leetronex 87The 24th Leeds Electronics Exhibition (Leetronex) takes place at

the Department of Electrical and Electronic Engineering,University of Leeds, between 30th June and 2nd of July. With over

100 exhibitors and a programme of lectures, the organizers areaiming to re-establish it as the best electronics show outside


The exhibition was created in 1963through requests from a number ofelectronics instrument manufacturers

who wanted to demonstrate their equipmentto the expanding higher education market.The equipment was shown to a selectedaudience of university staff. The event was sosuccessful that it was repeated the followingyear and Leetronix became established. Itgrew to a peak of several thousands ofvisitors from all over the UK in 1979.

The economic recession of the early 1980sreduced the number of exhibitors and visi-tors. Last year, the Department of Electricaland Electronic Engineering took over therunning of the show and made a major effortto re-establish it as "the best electronics

exhibition outside London." The 1986 ex-hibition increased its attendance by nearly50% over the previous year. The presence ofover 100 exhibitors this year suggests thattheir efforts have been rewarded.

The re -introduction of a programme ofseminars, organized by the Yorkshirebranch of the IEE, also helped to restablishthe status of the show, already the longestrunning electronics exhibition in the UK.

The exhibition has several qualities thatdistinguish it from other shows; Any profit isused to improve the undergraduate teachingfacilities; last year's profits were used toenhance the computer teaching laboratory.The show is supported by a number ofleading national and international corn-

panies and offers a link between industry andhigher education.


Lectutes, sponsored by the Department andthe Yorkshire Centre of the IEE, will takeplace in the Lecture Theatre (room 192) onthe first floor.Tuesday 30th June1100hThe changing technology of electronic com-ponents and assemblies.H.W. Ellis, Mullard Ltd.1400hCustomized design of integrated circuits.P. Forshaw, Ferranti MicroelectronicsCentre.Wednesday 1st July1100hDBS receiver architecture and technology.D.W. Walton. Thorn -EMI Ferguson Ltd.1400hSatellite tv - the present and the future.J. Hazell, British Telecom.Thursday 2nd July1100hModern tools for microprocessor softwaredevelopment.L.M. O'Carroll, Computer engineeringgroup, DE& E E. University of Leeds.



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4Mbit chip uses`trench cell'

The first laboratory samples havebeen produced for a dynamicram chip that can store fourmillion bits of data. Produced bySiemens in collaboration withPhilips, the 4Mbit d -ram uses a'trench cell' in which a trenchonly one micron wide is etchedfour microns deep into the sili-con. Each trench cell, with acapacitance of 40fF, stores onebinary digit and occupies an areaof only 5p.m2.

To obtain the more than 4million memory cells on a siliconchip, 450 process steps in c-mostechnology are necessary. Com-pared with the 1Mbit d -ram(54mm2), the storage capacity ofthe 4Mbit device is quadrupledwithout doubling the chip area(91mm2). Typically the 4Mbitchip can store the equivalentcontent of about 250 pages oftypewritten text.

The Siemens part of the pro-ject has been supported by theGerman government to the tuneof DM240 million. Production isexpected in 1989.


broadenedThe Engineering Council has setup a register for people who havegained either a degree, a HigherNational Certificate or a NationalCertificate in engineering as thefirst step towards becoming aqualified engineer.

Up to now the Council, whichhas 300,000 Chartered En-gineers, Technician Engineersand Engineering Technicians onits official register, has reg-istered engineers in those threecategories only after they havecompleted three stages: achievedthe exemplified academic stan-dard (known as Stage 1), com-pleted an approved trainingperiod (Stage 2), and gainedacceptable experience and pro-fessional responsibility (Stage 3).Now the Council's board forengineers' registration hasapproved the first list of candi-dates for registration at the Stage1 academic level.

Professor Jack Levy, the Coun-cil's director for the engineering

[UPDATEprofession, said: "We have thelargest professional register ofmembers in the United King-dom, but the country needsmany more to help us improvethe competitiveness of Britishindustry. We have already per-suaded the Government to pro-vide more engineering studentplaces in universities andpolytechnics but we are pressingfor even more."

He stresses the importance ofregistering as soon as possibleafter gaining a recognised de-gree, Higher National Certificateor National Certificate qualifica-tion so that they quickly proceedto becoming qualified engineersin one of the three categories.The Council and the professionalengineering institutions adviseand encourage young entrants.

"Our titles and designatoryletters of Chartered Engineer(CEng), Technician Engineer(TEng) and Engineering Techni-cian (Eng Tech) are recognisedguides to employers and othersof the competence and standardsachieved by registered en-gineers," says Prof. Levy. "Wenow urge the larger numberswho are completing their educa-tion in engineering and technol-ogy to register with us." En-gineering Council, 10 MaltraversStreet, London WC2R 3ER. Tel:01-240 7891.


Development has been designedto extend the applications of theinteractive video system andDomesday discs developed by theBBC, Philips and Acorn Compu-ters.

A new videodisc provides theusers with a practical guide toecology, taking as its basis thesimulation of a Devon naturereserve. The 'Ecodisc' enablesusers to draft a plan for manage-ment of the reserve and its activi-ties by discovering, learning andapplying ecological knowledgeand concepts.

Floppy -disc software offers en-hanced facilities for the use ofthe Domesday discs. One enablesthe extraction of relevant pic-tures and information which canthen be displayed independently.In autumn a further softwarepackage will enable users to inte-grate their own information with

the maps included on the discs.Next year, an additional disc

for the Domesday system willcontain detailed maps down tostreet level with updated and newdata sets for specific sectors ofindustry and commerce.

Spray -on super-conductors

Scientists at IBM have found away to spray -paint large andcomplex surfaces with high-

temperature superconductormaterial. This raises the prospectof inexpensive, easy -to -applymagnetic shielding, computerwiring and other applicationsthat might benefit from its prop-erties and workability.

IBM has coated items of va-rious sizes using an industrialtechnique called plasmaspraying. Plasma spraying quick-ly heats a material to thousandsof degrees and instantly depositsthe substance on a surface whereit resolidifies. After coating, ob-jects are reheated to anneal thesurface. At this stage the coatingbecomes superconductive. Thematerial's superconductingproperties were discovered lastyear, and the researchers believethey are the first to quickly andeasily coat complex shapes suchas pre -formed wires, contouredand flat surfaces and even tubesmade from ceramic. quartz andmetals.

The materials, combinationsof yttrium, barium and copperoxides, resemble flat black paint.After annealing, they become su-perconducting in the tempera-ture range of liquid nitrogen -'warm' enough to be practical formany scientific and industrialuses. (Liquid nitrogen boils at77K.) Most materials and wiresthat IBM researchers have coatedbecome completely supercon-ducting at temperatures as highas between 60 and 82K. In addi-tion to their ability to pass cur-rent without resistance, super-conductors are impervious tomagnetic fields, and might serveas an easy -to -apply and econo-mical magnetic shielding. Su-perconducting wires for compu-ter chip packages might also bemade by plasma spraying. Coatedthin lines have been added toceramic substrates used for inte-grated circuits and microscopicholes have been successfullycoated.


22 - 26 June 1987Laser 87 Opto-electronics, mic-rowaves.8th International congress andexhibition. Munich Trade FairCentre, F.R. Germany, MMA,Messegelande, Postfach 12 10 09.0-8000 Munchen. FRG.23 - 25 June 1987KBS 87 & Software Tools 87.Knowledge -based systems andsoftware. Wembley ExhibitionCentre, London. Online Interna-tional, Tel: 01-868 4466.24 - 26 June 1987APRS Show, (professional soundrecording) Olympia. London.24 -27June 1987SMT 87 Berlin: Surface mounttechnologies, International Con-gress Centre, Berlin. Details fromAMK Berline, Postfach 19 17 40,Messedamm 22, D-1000, Berlin19, FRG.26-30 June 1987BKSTS 87. 10th internationalfilm and tv technology confer-ence and Exhibition, MetropoleHotel. Brighton, BKSTS. Tel: 01242 8400.30 June -2 JulyLeetronex '87 the 'premier ex-hibition of the North' Leeds Uni-versity. Tel: 0532 431751 ex 328.30 June -3JulyExhibition of electronic musicalinstruments and systems at theLondon College of Furniture,Commercial Road, London El.4 -16JulyElectronic Design AutomationShow, Wembley ExhibitionCentre.7July 1987World final of the Micromousecompetition, Maze -solving, selfpropelled computers will be run-ning round the IEE. Savoy Place,London El at 1730h. Furtherdetails, and rules and entryforms, from Andrew Wilson atthe Institution. Tel: 01 240 1871Ext. 260.28 August -6 SeptemberFunkausstellung; Internationalaudio and video fair Berlin (in-corporating MediaForum), Inter-national Congress Centre, Ber-lin. Details from AMK Berlin,Postfach 19 17 40, Messedamm22, D-1000, Berlin 19. FRG.15-18 September 1987Design Engineering Show, NEC,Birmingham, Cahners Exhibi-tions. Tel: 01 891 5051.EED 87. electronics in engineer-ing design, NEC, Birmingham,Cahners as above.Test and transducer; internation-al conference and exhibition.Wembley Conference Centre,London. Trident International.Tel: 0822 4671


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X-rays can pre-ionize lasers

The use of X-rays to pre -ionizethe carbon dioxide gas of high-powered pulsed lasers is beinginvestigated at the British Aero-space Sowerby Research Centre.

Conventionally, gas preioni-zation is achieved by subjectingthe gas to ultra -violet radia-tion produced by spark dis-charges triggered off within thecavity of the laser. The researchcentre has produced the sameeffect by subjecting the gas toX-rays instead of ultra -violetradiation. Among the advantagesof this is that greater volumes ofgas can be ionized, enabling las-ers of much higher intensity tobe developed.

The area where the pre -ionization occurs can be deter-mined with greater precision,


leading to more efficient ener-gizing of the laser. Laser tubescan be simplified, as only twoelectrodes are needed, and thelaser gas remains purer as u -vradiation can cause the gases todissociate.

Experimental CO2 laser with x-ray pre -ionization is claimed byBritish Aerospace's Sowerbyresearch laboratories todemonstrate greater laserefficiency and less gasdissociation.


23-27 September 1987PCW 87; 10th Personal Compu-ter World Show, Olympia,London.29 September -1 October 1987NAV 87. Navigation data, dis-semination and display confer-ence and exhibition, HeathrowPenta Hotel, Organized by theRoyal Institute of Navigation.Tel: 01-5895021.Semiconductor International:design, assembly, test, materialsand chemicals. NEC Birming-ham, Cahners Exhibition, Tel:01-8915051.5 -8 October 1987HDTV 87; International collo-quium, Ottawa, Canada. Detailsfrom HDTV colloquium. JournalTower North, 300 Slater Street,Ottawa, Ontario K1A OCB,Canada.


A high proportion of this year'sQueen's Awards for Technologyhave gone to electronics com-panies.

Integrated switching. AB Auto-motive Products for theirprocessor -controlled switchingsystem for use in cars. The sys-tem for the Jaguar X.I40 has over200 auxiliary items that requireswitching.

ISO network system. BICC DataNetworks for the development ofthe Isolan system of hardwareand software links for a local -area network that conforms tothe ISO standards. The systemallows the mixing of coaxial andoptical fibre cables within onenetwork.

Computer -controlled looms.Bonas Machine Company forcomputer -aided patterning forJacquard fabric weaving looms.Designs can be programmed in afew hours compared with fourdays for the old punched -cardsystem.

Radio -controlled switching. TheBBC in collaboration with theElectricity Council for remoteswitching of lItctricity timeswitches. Low -frequency signalsare added to the BBC's long andmedium -wave broadcasts with-out affecting the audible signals.

Heat -detection system. RoyalSignals and Radar Establishmentin collaboration with EEV tubesfor the development of heat de-tecting video cameras. Thepyroelectric vidicon tube is cap-able of detecting temperaturedifferences as little as 10-3°C.

Night vision (twice). RSRE/EEVare also responsible for theaward -winning night -vision sys-tem for aircraft, using new imageintensifier tubes. Also The RoyalAircraft Establishment for theirnight vision system uses infra-red sensors, night -vision gogglesand head -up visual displays.

SMC autoplacement. DynapertPrecima for automatic place-ment of surface -mounted com-ponents. Machines can place upto 6000 components in an hourand can be programmed tohandle up to 120 different com-ponents types.

Oil reserve simulation. Explora-tion Consultants of Henley onThames for Eclipse computersimulations of gas and oil re-serves.

Surface -mounted p.c.bs. Fer-ranti Computer Systems formetal -core multilayer p.c.bs thatavoid the problems of thermalexpansion and heat dissipation.

Computer -controlled cam lathe.The Litton UK camshaft systemautomatically compensates forgrinding -wheel wear and

achieves much higher accuraciesthan previously possible.

CD mastering. Nimbus Recordsfor developing their own systemof mastering compact discs, in-volving coating the masters withphotoresist 0.12µm thick, en-coding of digital signals to con-trol the laser writing beam, con-struction and control of themastering lathe and control ofthe plating process. It cost abouta tenth of the alternative system,exceeds the capabilities of thatsystem and meets the expectedrequirements of the next genera-tion of CDs.

Colour radar. Racal Marine Datafor a digital scan converter incolour radar displays. It proces-ses derived from a conventionalradar scanner to be displayed in ahigh -resolution colour tv for-mat. The system combines high-speed computing, video proces-sing and memory managementinto a single small unit.

Self -calibrating data recorder.Racal Recorders for its Store-house tape recorder for data ac-quisition. Its automatic calibra-tion system allows the recordand replay circuits to be set up inless than ten minutes instead ofthe hours previously needed.

Optical -fibre lasers. STC De-fence Systems for 1300m lasersfor optical fibre communication.The devices allow repeaters to be30km apart at a data rate of

565Mbit/s, i.e. twice the rangeand four times the speed of for-mer devices. They are claimed tobe the sub-merged use.

Aircraft simulators. SingerLink -Miles Ltd for functionallydistributed simulation systemfor aircraft training. Processorsare linked to provide real-timecomputing power beyond thescope of super -mini computers.the system is used in the firstsimulator for the new Boeing747-400.

Network manager. Tech-NelData Products Ltd. of Banbury.the NMX Network ManagementEngine which integrates hard-ware and software systems know-ledge for fault detection, restor-ing, and diagnostics in a singleprocessor -based fault -tolerantdata communications.

Magnets for spectrometersVG Analytical Ltd. for the de-velopment of laminated magnetsfor fast -scanning mass spectro-meters. Existing magnets offeredlimitations in meeting the de-mands of capillary column gaschromatography. The companydeveloped lamination andmachining techniques to pro-duce magnets assembled from100 or more 0.3mm thicklaminations. They meet the newrequirements of medical and en-vironmental biochemical analy-sis equipment.


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Advertisem*ntsaccepted up to 12noon June 26 for

August issue

DISPLAYED APPOINTMENTS VACANT: £23 per single col. centimetre i min. 3cm ).LINE advertisem*nts (run on): £5 per line, minimum £40 (prepayable).BOX NUMBERS: El I extra. ( Replies should be addressed to the Box Number in theadvertisem*nt, c a Quadrant House. The Quadrant, Sutton. Surrey SM2 5AS).PHONE: SUSAN PLATTS, 01-661 3033 (DIRECT LINE)

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Britain's premier motoring organisation providesa broad range of services to its 2.5m members.and is committed to new technology in achieving

growth and higher standards.A senior telecommunications engineer with a background inVHF or UHF radio systems. ideally involving data transmissionand aerial site selection. is now required for the new post ofRadio Development Manager. Having technical responsibilityfor the RAC's Computer Aided Rescue Service (CARS) project,the successful candidate will be a key part of the teamintroducing change and technical innovation. Age indicator26-45.Salary neg c.£17K + car, non-contributory pension, life andmedical insurance. Assistance with relocation wherenecessary.For further information and application form please telephone(0753) 867175 (24 hrs) or write to Alex Villiers, 3i ConsultantsLimited, 8 High Street. Windsor. Berks SL4 1LID. quotingref AV/674.

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Professional Career OpportunitiesThe Easy Way to look for your new job from thecomfort of your own armchair. Our well qualifiedconsultants will carefully match yourrequirements againstappropriate vacancies. cAmE

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CLIVEDENPROCESSOR BASEDWEIGHING EQUIPMENTTest 8 repair of food weighing systems£8,000 HampshireCELLULAR TELEPHONE SYSTEMSExperience of fault-finding analogueand digital systems. Training offered onA T.E£12,000 SurreyTELEPHONE EXCHANGESService and maintain PABX systemsthroughout so.rthern England.to £10.000 - car BerkshireTRAFFIC AUTOMATIONFault find and repair of digital controlsystems throughout the U.K.00.060 car MiddlesexCOMPUTER PERIPHERALSRepair a wide range of disc and tapedrives£8,000 BerkshireDOCUMENT READER SYSTEMSExperience in the repair of digital andmicroprocessor equipment both in theU.K and overseas.£12,000 Hampshire

Hundreds of other Electronic andComputer vacancies to £15.000.

Phone or write:Roger Howard C.Eng. M.I.E.E. M.I.E.R.E.

CLIVEDEN RECRUITMENT92 Broadway. Bracknell.

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THE HATFIELD POLYTECHNICSCHOOL OF NATURALSCIENCES. Senior Technician -Electronics. Salary £7,536-£9,441. To beresponsible for a small ElectronicsWorkshop. The successful candidate mustbe an experienced electronics techniciancapable of fault-finding down tocomponent level and with a generalknowledge of scientific equipment. Startingsalary dependent upon qualifications andexperience. Closing date: 15 July 1987.Application forms and further details fromthe Staffing Office, The HatfieldPolytechnic, PO Box 109, Hatfield, Herts.ALIO 9Ab. or telephone Hatfield (07072)79802. Please quote reference: 291. 464

Project Engineering:The Mercury Challenge


In under five yearsMercury Communications,part of the world-wideCable and Wireless groupof companies, hasprogressed from originalconcept to a position where

it offers a viable alternative telecommunications service. But it does notend there. Today we are still committed to continued growth involvingfurther, major, investment in facilities.

With our total commitment to digital technology, high capacity opticalfibre cable and microwave links we can offer the kind of professionalchallenge you will find hard to equal today.

PROJECT ENGINEERSOur London based team now has a few vacancies for Engineers tomeet the challenge of our technology and fully utilise their skills.Reporting to a Senior Project Engineer your role will include workingwith the Design Function both on design work and equipment details,dealing with suppliers in conjunction with other departments onprocurement matters and producing progress and status reports.

RADIO SYSTEM COMMISSIONING ENGINEEROur London team has vacancies for Field Based Engineers.

Your main role will be the commissioning of complex digital radiosystems and testing of alarms on a SCADA network throughout the UK.Extensive travel will be necessary.

Experience - five years' telecommunications experience, a recognisedtechnical qualification and knowledge of digital systems, ideally withhands on experience of microwave power and radio systems. Goodcommunication skills, commercial awareness and time spent in a projectenvironment would be useful. Current driving licence is essential.

In addition to an attractive negotiable salary there is an excellentbenefits package and outstanding prospectsPlease send a full CV to Susan Tomlinson,Mercury Communications Limited, St. Martin's House,140 Tottenham Court Road, London \X/1P 9LN,or for any furher information call on 01-387 9191, ext. 309.

Hardware/Software/SystemsL9,000- £25,000

As a leading recruitment consultancy we hove a wide selection of opportunitiesfor high calibre Design, Development, Systems ond supporting staff throughout the UK.

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Opportunities exist with National, International and Consultancy companies offeringexcellent salaries and career advancement.

To be considered for these and other reguiremeni. contact John S;Stephen Mor ev or forward a detailed CV in complete confidence auot, IRef. WW /66.

A STS Recruitment, 85 High Street, Winchester,Hants 5023 9AP. Tel: (0962) 69478(24 hrs).


ELECTRONICS WORKSHOPTECHNICIAN (Grade 5) required in theUniversity of Reading, Department ofPsychology. From mid -September 1987.The successful applicant will be required toadvise staff and students on electronicsproblems and to design and construct awide range of specialised equipment. TheDepartmental research and teachingactivities depend heavily on the use of

computers. The ideal candidate will havehad a recognised apprentice and at least 2years of varied experienced in electronics.Knowledge of BBC BASIC and of 6502would be an advantage. Salary scale £7696to £9086b p.a. Application form availablefrom the Personnel Officer, University ofReading, Whiteknights, PO Box 217.Reading, RG6 2AH, telephone (0734)875123 ext. 220. Please quote Ref. T.30A.








TELEPHONE: 445 0749/445 2713HENSON LTD.

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Sutton,Surrey SM2 5AS


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BEMUniversity of Wales

MSc in Electronic EngineeringAnalogue and Digital Systems; Computer

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Engineering; Control and Instrumentation;Medical Electronics; Integrated Circuits;

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Diploma in Electronic Engineering(successful completion allowing entry to

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Applications are invited for places on theabove full-time, one-year courses

commencing in October 1987.Further details and application forms may

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PO Box 68, Cardiff CFI 3XA 4S8

INTELLIGENT SELF -MOTIVATING PERSON WANTED inlarge successful CD shop in central London for service andsales of CD players and audio equipment. Relevant City andGuilds, TEC or ONC qualification will be taken into consider-ation. Practical experience in digital equipment would be anadvantage.Please phone in first instance to Mr Hosein or Mr Bullat Covent Garden Records on 01-379 7635/7427


WANTEDTest equipment, receivers,valves, transmitters, com-ponents, cable andelectronic scrap and quan-tity. Prompt service andcash. Member of A.R.R.A.

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On Friday 10th July at 12:00 noonJOHN RUSSELL 8 CO will hold an


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' 01-640 4424 for catalogues.Auctioneers:

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e you looking for a secure snore -based lob whicn offersrewording career in the forefront of modern Tele-

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BRIDGES waveformn/transistoranalysers. Calibrators, Standards.Millivoltmeters. Dynamometers. KWmeters, Oscilloscopes. Recorders.Signal generators - sweep, lowdistortion, true RMS, audio, RM,deviation. Tel: 040 376236. (26161

3 Si " FLOPPY DRIVESMITSUBISHI top quality new 3millisecond 80 track, only 32mm high,standard interface, will directly interfacewith PC's and will give 720K per disc. Veryquiet. Guaranteed in makers packingunopened. These are the best quality drivesavailable. £80 with full specs. Call 010 3532188 8231. Access, Visa, Mastercard.Eurocard. 455


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G.W.M. RADIO LTD40 42 Portland Road. Worthing. Sussex.

Tel: 0903 34897

tiers Receivers lest equipment components etcPye pocketrone PFI TX units with battery and circuitsC12 inc pap En 13T Meters Type r Tester SA 90835V50V'250V DC 250V AC/50rnA500rnA5A DC Lowand high ohms nets trom 2AA batts C9 as pap Type2 I2D 19 ranges 1-250V DC 10.1.000V AC 3 ohmsranges plus 0 05-1A DC 20K ohms V DC 16 ohmsV AC £13 inc pop Type 3 SA 908314 electronic550'2505 DC 059 5 5A DC 2500 AC 3 1low ohms andIM ohm range £16 Inc pap All meter movementschecked and supplied with leather case and jai, leads

P.C.B. ARTWORK DESIGNSERVICES. All requirements from:- SS1DS 1 ML & Screens & resists circuit - logic(redrawing NR) to:- Usts, prototypes &static tests. Liaison W.R.T. observed errors,problems. D.F.Busk Hillsdale, Green Lane.Letchworth SG6 1'40(0462) 682154. 456

P.C.B's DESIGNED. Artworkcapacity available for singledoublesided, P.T.H. and multi -layer P.C.B.'s,also silk screens, solder masks, labelsetc. For C.A.D./Photoplot, artwork &photography, contact Mr. Williams. 49Westbourne. Honeybourne. Evesham.W,01, W1111 5PT Ti.l?0386 s:12 I 7,2


As fromSeptember issueClassified rates

will be!25 per scc.

Lineage £5.50per line.

Box No. £12extra.

TURN YOUR SURPLUS i.cstransistors etc. into cash, immediatesettlement. We also welcome theopportunity to quote for completefactory clearance. Contact COLES-HARDING & CO, 103 South Brink,Wisbech, Cambs. 0945 584188. (921

PRINTED CIRCUIT BOARDSsingle and double sided manufacturedto your specifications. We offer qualitand fast service (same day onprototypes) at very keen prices. Wesupply copperclad material cut to size.Artwork service available. MondoCircuits Ltd. 35 Grossenor Rd,Twirkinham, Middx. 01-891 5412 413


Simple assemblies, PCBs.modules, or complete units.

Wide range of circuit techniquesand power levels.

Support and advice serviceWe offer a careful professional

service. at a careful price.T & B Services.

18 Ashlin Grove. Lincoln. LN1 1LE.(0522)39708

Please telephone or write torFREE HELPFUL INFORMATION.



Particularly medium -wavetransmitters, FM transmitters,

studio links (STL), studiofurniture, affects, cartmachines, AA3 carts.


CAMBERLEY. SURREYTel: 0276 29219 404

BILLINGTON VALVESNEW VALVE& TRANSISTORS tiugerange stocked Rarities our speciality Phone toimmediate qLotation. on any type SAE forcatalogueUSED VALVES - Tested. working c lean. 28day guarante.. KT66 GEC a FICHE (MazdaCV4055) C3. 12E1 C6-90 CV4024 M Alard (WaalO ECC8I 18Co. CV4003 Mullard (sp-ecialECC82) 70p All excluding VAT We will buyvalves compete shop clearance etcUSED TEKTRONIX 465 DUAL TRICESCOPE - 1011MHz As new condition. worksperfectly. mitt probes and lid £750 deliveredexcluding VA!'NEW ELECTROLYTIC CAPACITORS - Goulc10.000 MFD w 50V. 18 7 Amp disci arge Specsalquality for computer use etc Usually C8 -C12Our price C4 VAT deliveredNEW AUTO 'RANSFORMERS - eg

In 0 115 200 210 220 230 240 25(Out - 115V Or 13 05A. or 200-2501 ar 7 5A

C25 deliverec excluding VATMany transformers in stock, constant voltage.autos. multdaps etc. etc. List available duringJuly or phone your enquiry1.000 resistors or 1.000 capacitors - C3 50 VATdeliveredMixed parcel of IC transistors relays...apacdors resistors. potentiometers switches.2 569 - C5 VAT delivered. 10Kg - CIO VATdelivered

Billington Valves, 39 Highlands Road,Horsham, W Sussex RH13 5LS.Tel: 0403 210729: Fax 0403 210108:Telex, 87271 PRODSS G.Callers welcome by appointment.We accept Barclaycard Govt and export orderswelcome


Buyers and Disposal Officerscontact:

COOKE INTERNATIONALUnit 4, Fordingbridge Site

Ma n Road, BarnhamBognor Regis

West Sussex P022 OEBTel: 0243 685111 2

Stock iist available, send 50pto cover p&p.


'.thantity ot manuals sho w1,1' .130,11f0n/ orf'of000py service etc Sanyo 60W IC amps N.

sgh output negative -an generator [45. Audio &Hi generators 14 11 capacitors Vacuum pumpEN. Diffuswon pump 9311. Electrostatic voltmeter00. Ignition Analyser C39. AuloManual 35mmSLR camera C79. electronic flash CIO both usedin colour Photomicrography Hap power strop,scope with sync facility used in hqh speed andslow motion colour video 6 ttlm ecorong photo-graphy 1135. Calibration standard rex (unused)£12.50. Miniature Matsubshe motor generators£2.75, reversible output & rotation dacha speedcontrol etc I Miniature flash A detonator gener-ators single stroke. high speed return. integralgearbox with capacitance 6 auto smith N. handoperated LCR Bridge Centrifuge Record Oise)cumng machines EMI MSS & BBC,Grampan£100ee. Binocular ComParatorrstereo examina-tion equipment £55. Aircraft Radio Test Set 05.lonesabon chamber with 3 -stage ampliker £25.chamber only C20. Record chart recorder withinterchangeable mains and Clockwork dnves [99.Wayne -Kerr RF Generator 5-100 MHz (very com-pact) ShaoweigN Indust.' Balance [45. Muir.head Multi -Ratio RF Bridge £65. DensrlorneterC35. Binocular 6 Monocular rocrscopes 1 Re-cording Tape or NAB spools O. OscilloscopePhaserneter £69. Last few Bkie Steel Rocketsections 5 for £50. NOUSE ,LABORATORvSMALL FACTnny OrrtCF PRFNI,FS for sale in



Dome Tweeters, Dome Mid -Range,Woofers and Sub -Woofers.

Uniquely EngineeredAluminium Voice Coils

For further information, pleasephone: 0473 719212 ,

INTEGRATED CIRCUITS: Largequantities for sale guaranteed in makerspacking, Top quality Hitachi HM65256AP-20 pseudo static RAM, NEC D80C42Cprogrammable microprocessor, INTELP80088 CMOS microprocessor. SMCFDC765AC floppy disk controller. Theseare all from discontinued product of topquality manufacturer. Call 010 35321873304. 457



Quadrant House.


The Quadrant.



To "Electronics & Wireless World" Classified

Rate £5 PER LINE. Average six words per line.Minimum £40 (prepayable).

Name and address to be included in charge ifused in advertisem*nt.

Box No. Allow two words plus £11. Cheques, etc., payable to "Reed Business

Publishing" and cross "& Co." 15% VAT tobe added.


Sutton. Surrey SM2 5AS

for yourADVERTIsem*nT

Advertisem*nt Dept..






& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (106)

MATMOS LTD, 1 Church Street, Cuckfield, West Sussex RH17 5JZ.Tel: (0444) 414484/454377

COMPUTER APPRECIATION, 111 Northgate, Canterbury. Kent CT1 1BHTel: Canterbury (0227) 470512. Telex: 966134 COMPAP G

PLESSEY Model T24 V22./V22 bis MODEM. Compact. automatic modem featuring the latesttechnology and the highest possible data rate over the ordinary phone system Offers both V22and V22 bis compatibility 12002400 Baud operation with auto bit rate recognition. operation on bothordinary phone IPSTNI and private circuit (PC) auto call and auto answer. duplex operationallowing simultaneous transmission and reception of data at 2400 Baud in both directions over asingle phone line, compact size 19 9 2' 2 1 BT approved BRAND NEW £350.00VICTOR SpeedPac IBM PC ACCELERATOR Half -wide 80286 accelerator card for IBM PC andcompatibles With 8kbyte cache memory and 7 2MHz 80286 processor Offers AT:PersonalSystem 2 performance for a traction of the cost Runs up to 7 5 times faster BRAND NEW C199.00ITT SCRIBE III WORD PROCESSING SYSTEM Professional system originally selling ataround 06.000 without printer Now offered with software Included and a variety of differingoptions (including hard disc. comms etc) available This system is available from us ALLBRAND NEW at the cost of current budget systems. but with office -quality performance andfeatures With dual processor workstation ( TI 9995 and Z8OHI 12 green display with slowscrolling. 128kbytes RAM. dual 500kbyte SHUGART 5, a' floppy disc drives and comprehensivesoftware C290.00SAMURAI Model S16 computer 8086 based 128k true 16 bit machine with twin 8" NEC floppydisc drives (total 2.5 mbytes. IBM 3740 compatible). monochrome (green) high resolutionmonitor. 2 RS232 interlace. CENTRONICS parallelinterf aces and MSDOS with lull set ofmanuals We have now sold out of complete machines. but have about half a dozen withoutkeyboards available C95.00TOSHIBA Model T300 PC SYSTEMS 8088 (6MHz) based system with 192kb memory. 2, halfheight DSDD floppy disc drives each of 655kb capacity (unformatted). high resolution greendisplay 25 , 80 characters. RS232 and CENTRONICS parallel interfaces MS-DOS Ver 2 andT -BASIC are included together with a diagnostic disc and manuals We have low cost packagesavailable now, including Word processing. Spreadsheet etc BRAND NEW £295.00AS ABOVE. but with single floppy disc drive C249.00TOSHIBA Model T100 CP/M SYSTEM. With 64kb RAM dual 500kb 5' a floppy disc drives.serial and parallel interlaces. BRAND NEW C149.00MATMOS TERMINAL MATMOS PC with Ver 2 EPROM for terminal emulation Probably thelowest cost terminal available anywhere With set-up menu and with data rates up to 9600 BaudMachine is easily modified for split Baud rate operation 75/1200B. EPROM plugs into ROM socketaccessible from exterior Emulation is VT -52 compatible for cursor addressing. and for characterattributes as far as the MATMOS PC allows MICROSOFT BASIC is still available from thekeyboard (EPROM card on its own. 020.00. EPROM card with socket only for users ownEPROM 08.00 BRAND NEW C69.00HITACHI Model 305S/SX 3" disc drives With SHUGART compatible interface as for 5' 4drives Uncased 125K (single density) or 250K (double density). 40 track, 100 tpi. soft sector.3ms track to track time. standard 34 way edge connector. 12V and 5V powered (standardconnector) with overall 3 7W typical power consumption These drives have been tested by us onthe BBC with DES. on the AMSTRAD 6128 and on the TATUNG EINSTEIN. and are alsoknown to be suitable for the AMSTRAD 664 and as a second drive for the AMSTRAD 464.Single -sided. 250kb unformatted BRAND NEW Data cables are available from us tor theAMSTRAD 6128 and BBC at £7.50. and an installation pack including data and power cables withinstructions is available for the TATUNG Einstein at C12.00 C24.95CANON Model MD0220 TWIN 51/4' FLOPPY DRIVES. Cased BRAND NEW half heightdrives. double sided. double density. 80 track. 640kb capacity per disc Shugart compatibleinterface. without PSU. per pair . C99.50KIMTRON Model ADM 85H VDU 24v80 intelligent VDU with TELEVIDEO 920/925 emulationFeatures include. non-volative set-up with status line. auxiliary port. all Baud rates 50-19200Baud cursor addressing. etc 0185.00

DEC PDP 11/23 SYSTEM with DLV11-J quad serial interface. TANDON 8 floppy with MICRODE V ASSOCS Model MXV-21 controller. FWITSU 8 Winchester disc drive with DILOG00401 controller 256kb memory Contained in 2'19 rack units in portable carrying caseSupplied with XENIX operating system complete with all original manuals and distributiondiscs C1,385.00ATARI Model 1024 STF personal computer with Model SC1224 medium resolutioncolour monitor. With 1101 simulator plus all usual software Originally purchased 1987 and asnew £565.00CALCOMP Model 463 AO graph plotter C325.00TOSHIBA HIGH RESOLUTION COLOUR MONITOR IBM compatible with RGB inputBRAND NEW C169.00TOSHIBA LOW RESOLUTION COLOUR MONITOR IBM compatible with RGB input BRANDNEW £95.00APPLE PROFILE 5mbyte WINCHESTER disc drive for APPLE II computers Complete withProDos operating system aid additional interface for APPLE II C275.00FUJITSU Model M2230AS 51/4 WINCHESTER disc drive 6 66mbyte capacity unformatted16/32 sectors 320 cylinders With ST506 interface BRAND NEWDEC Model VT101 VDU with many features including non-volatile sel-up slow scrolling etc £150.00.DEC Model BA I 1 MF box power supply and 8 slot backplance for 0 -bus BRAND NEW C185.00ADAC Model 1822 128kbyte CMOS memory for 0 -bus With battery backup C175.00TEKTRONIX Model 7603 100MHz OSCILLOSCOPE MAINFRAME with CRT readout £590.00TEKTRONIX Model 7403N 60MHz OSCILLOSCOPE MAINFRAME £250.00TEKTRONIX Model 7A17 75MHz 5mV dual trace amplifier. C175.00TEKTRONIX Model 7A18N As above. but without CRT readout £150.00TEKTRONIX Model 7B53A 100MHz dual timebase 0295.00TEKTRONIX Model 7012 A/C) converter with M2 sample/hold module C550.00TEKTRONIX Model 5403/015 60MHz oscilloscope with 2 5A48 A 5E142 £750.00TEKTRONIX Model 5103/015 2MHz single beam storage oscilloscope with 2 - 5A18N and5B1ON £550.00HATFIELD INSTRUMENTS Type 2105 50 Ohm affenualor £40.00BRYANS Model 45000 UV recorder with 6 45001 amplifiers 1 mV/cm.50V/cm and chartspeeds from 1 mm/min-500mmis Timing line interval is adjustable from 0.02s -10s and RecordDuration 0 5s -20s With remote control facility C195.00TEKTRONIX Model 851 digital tester One knob lets you dial 22 functions 11 functionsmeasure timing two register plus and minus peak voltages three carry out DMM measurements

and one reads line voltage at the outlet the 851 measures its 4 input thresholds to adjust tothe logic levels of the equipment being serviced 5, 2 digit readout 35Mhz frequency/timing.autoranging etcHEWLETT PACKARD Model 59307A dual VHF switch DC to 500MHz 50 Ohm switch for HP -113 C185.00HEWLETT PACKARD Model 5045A digital IC tester with CONTREL H310 automatichandler With IEE interface and print out of test results either pass/fail or full diagnostic includingpin voltages at point of !allure With full complement of pin driver cards and complete withsubstantial library of mag card test programs for 74 series TTL and other ICs CONTREL handlerallows fully automatic tes ing of ICs which are sorted into 2 bins Price includes a secondHP5045A (believed fully operational) for maintenance back-up 01,950.00TEKTRONIX Model 577 SEMICONDUCTOR CURVE TRACER With 5 heads for variousdiodes and transistors In excellent condition £1,900.00TIME ELECTRONICS Model 9810 programmable power supply C190.00TIME ELECTRONICS Model 505 DC current source 0 05°. With leather case 075.00PLEASE NOTE'VAT 6 carriage must be added to all prices. Please enquire for details.'All new equipment is guaranteed for 6 months.


INDEX TO ADVERTISERSAppointments Vacant Advertisem*nts appear on pages 764-767

PAGEAEL CrystalsAdcola Products LtdAdvertising Standards

Authority 760Airlink Transformers 700

Barrie Electronics 694Brigden Technology 749

Cambridge Kits 726Carston Electronics Ltd ....666,745Channel Micro Products Ltd 750Cirkit Holding Plc 669Computer Appreciation 768Crash Barrier 687Crotech Instrumentation Ltd 753

Display Electronics 714/715

PAGE726 E&WW Wall Chart 726669 E&WW Feature List 756

Electronic Brokers IFC,OBC

Field Electric Ltd 676Fluke (GB) Ltd Advert Card

GNC Electronics 694Golten and Verwer Partners 686Guyvale Ltd 686

Happy Memories 752Harrison Electronics 745Hart Electronics 749Henson, R. Ltd 700Henry's Audio Electronics 726

ILP Electronics Ltd. 686ICOM (UK) Ltd 745

E.A. Sowter 749EMS Manufacturing Ltd 752 Johns Radio 694

PAGEKestral Electronic Components

Ltd 756Lab -Volt 670Langrex Supplies 746Levell Electronics 687Livingston Hire 681MA Instruments 726Micro Concepts 720Microprocessor E ngi neeri ng 745Mikro Kit Ltd. 682

Number One Systems 700Nuvotem Teo 756

P M Components Ltd 724/725Pineapple Software 668Process Communicator

Loose insertQuart -hand 750RTT Systems Ltd 676Raedek Electronics 750

PAGERalfe Electronics 682Research Communication 668

Sherwood Data Systems 670Solex International 694Stewart of Reading 756Strumech Engineers 682Surrey Electronics Ltd 686

Taylor Bros (Oldham) 676Technomatic Ltd 758/759Telonic Instruments IBCThose Engineers Ltd 669,753Thurlby Electronics 752Triangle Digital Services 700

University of LeedsLoose insert

Webster Electronics 750Withers, R. Communication 753

Xen Electronics 760

OVERSEAS ADVERTIsem*nT AGENTSFrance and Belgium: Pierre Mussard, 18-20 Place de la Madeleine. Paris 75008.United States of America: Jay Feinman, Reed Business Publishing Ltd., 205 East 42nd Street. New York, NY 10017 - Telephone (212)867 2080 - Telex 23827.

Printed in Great Britain by E.T. Heron I Print) Ltd, Crittall Factory. Braintree Road, Witham, Essex CM8 3Q0, and typeset Ey Graphac Typesetting. 181,191 Garth Road, Morden, Surrey SM4 4LL,for the proprietors. Reed Business Publishing Ltd, Quadrant House, The Quadrant. Sutton, Surrey SM2 5AS. Reed Business Publishing Ltd 1987. Electronics and Wireless World can be obtainedfrom the following: AUSTRALIA and NEW ZEALAND; Gordon & Gotch Ltd. INDIA: A. H. Wheeler & Co. CANADA: The Wm, Dawson Subscription Service Ltd., Gordon& Gotch Ltd. SOUTHAFRICA: Central News Agency Ltd; William Dawson & Sons (S.A.) Ltd. UNITED STATES: Eastern News Distribution Inc., 14th Floor, I 1 1 Eighth Avenue, NewYork, N.Y. 10011.


& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (107)

Low cost electronicmeasuring instruments.TFG 81FUNCTION GENERATORS.


TFG 8101 gives sine, square. triangular, puts and rampoutputs over 0.1 Hz to 2Mz with output voltages up to 20Vpk-pl,TFG 8104 - all the features.of the TFG 8101 with 0-10( %ampl tude modulation and frequency modulation0 + 10.4




8 digit Frequency Counters' TFC 1201 10Hz-100MHz direct.TFC 1204 10Hz-80MHz dr-ect, 50MHz-650.41Hz with pre -scaler; TFC 1207 10Hz-80MHz direct, 50MHz-1000MHzwith pre -e cater.



Inexpensive DC Bench Ppwer Supplies wi h single or dualtracking iutputs or dual racking with fixes - 5 volt rail.Outputs DC to 30 volts orOC to 60 volts win output currents0-1. 0-2. 3-3. 0-6 or 0-10 imps. dependinc on model.

All prices + VAT



TFG 8111 -a combination Function Genera or andFrequency Cot rifer 0.1 Hz to 2MHz sine. scmare, triangular,pulse and ramp outputs. with a 100MHz 6 DV frequencycour.ter.

TFG 8114 - is -he TFG 8111, except 5 digit punter plusoutput frraqt ercies up to 5MHz and sweep, rigger, gate andburst functi



8 digit Univer!al Counter timers with frequency. period,inte-val, rev) and totalise functions. TFC 1211 5Hz-100MHzdirect. TFC 1214 5Hz-100MHz direct, 50Mrlz-650MHz withpre- scaler;TF: 1217 5Hz-100MHz direct. 5DMHz- 1200MHzwith pre-sc aler.




I 14.


Similar to he TPS 2000/4000 range but wth digital voltageand currer t measurement. Digital meter czn also be used asDVM

TopwardElectronic Measuring Instruments




TFG 4613 offers sine, square, triangular, ramp. pulse, A.M.,FM., =weep, trigger, gate, burst over 0.1Hz to 13MHz at upto 20v' pk-pk. Amazing value,




il-17111111 ad)

TM 104 - 3'h digit Bench Multimeter with 1(1 % 1

digit accuracy. Measures DC 8 AC volts and ct rrent andresigance. High 1000M I1 impedance.TM, 105 - 4'h digit true RMS Bench Multimeter with± (02,4% + 1 digit) accuracy. DC 8 AC voltage and currentplusaesistance measurement.



TM / 360 -a single channel AC Millivoltmeter with f.s.d.ran.ges from lmV to 300V and bandwidth 10H: to 1MHz.TM / 380 -a two channel instrument. f.s.d. rar ges 1 Mv to30CV and a 10Hz to 500KHz bandwidth.TM 1381 - also two channel, but f.s.d. ranges 31313µV to 100Vanc 5Hz to 1MHz bandwidth.

Telonic nstruments Ltd.Boyn Valley Road.

Maidenhead,Berks. SL6 4EG,

England.Tel: (0628) 73933

Telex: 849131Fax (0628) 770529

IENTIKII 2 ON 11E1'1,1' EA It I)

& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (108)


PHILIPSPM3302Real time or digitalstorage, withsampling rate20MHz, maxresolution 5Ons,2k x 8 bit memory,2 channels. WithIEEE option £2125.

PHILIPSPM325675MHz, compactruggedised portablescope with shoulderstrap, dual trace,2mV sensitivity,delayed time base,trigger view, 111triggering.

HAMEGHM60560MHz, dual trace,sweep delay,maximum sensitivityI mV, versatiletriggering,Z modulation, X -Yoperation, in-builtcomponent tester.



The world leader in 'scope technology', this 50MHzoscilloscope with true dual timebase offers features that makeit the smart choice for performance and simplicity.Features: True dual timebase, calibrated sweep delay, 16KVacceleration potential CRT, third channel (Trigger view),autoset of amplitude, timebase and triggering, SPECIALLCD panel, easy to use front panel design. OFFER

HAMEGHM205Real time to 20MHz,digital storage to10KHz, 1024 x 256point resolution onX and Y axes, singleand refresh modes,active video trigger.

GRUNDIGM02220MHz, dualchannel, automatictimebase selection,triggerable secondtimebase, hold -offcontrol andZ -modulation,TV triggering.


HAMEGHM203-620MHz, dual trace,2mV/cm maximumsensitivity, componenttester, add andinvert, automatic andnormal triggering,X -Y operation, with2 probes.


Also Available . 15MHz dual traceT 1handar TO315 5MHz battery porte £780 Phiii pmn?nAPhilips PM3267 100MHz dual traceabl£1627 Hameg HM208 20MHz D.S.O.


UK's No.1 Test Equipment Distribution Company0 Lif, 0

i7Electronic Brokers

L'=" Electronic Brokersn- -1 n- 140/146 Camden Street, London NW1 9PB= U Fax: 01-267 7363. Telex: 298694. Tel: 01-267 7070.

All prices exclude VAT and carriage and are correct at time of going to press. ry it 3 (iN tAlt1)

& WIRELESS WORLD...TF 2604 Voltmeter £425 TF 2702 Inductor Analyser £950 TF 2905/8 TV Pulse Generator £650 TF 2915 Data Monitor £1200 TF 2950/5 Mobile Radio T.S. £1350 Philips - [PDF Document] (2024)


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