eKtorgiectronico

68 -page supplement ofconstruction projects

The MAC SystemThe Compact Disc

EE JULY AUGUST 1987

PRODUCTS NEW PRODUCTS NOA new audio-phile qualityhigh fidelityamplifier kitThe GATE ONE amplifier kit is atop quality professionallyengineered amplifier that hasthe sonic performance, buildquality and finish of amplifiersin the £300 - £400 price range,yet costs only £161 inclusive.Available from GatehouseAudio, the amplifier specifi-cation includes a host offeatures common to most mid-range ready built amplifierscombined with various aspectsof design and performance nor-mally associated with moreesoteric products. A ready builtversion is available for £201.25.Features include a 40 + 40 wattoutput, a fully stabilised highcurrent power supply, high cur-rent TO3 power supply and out-put transistors, 225VA trans-former with 6 reservoircapacitors, double sided earthplane pcb, minimum capacitorpassive RIAA and tone controlequalisation, sub -sonic filter,low end bass boost switch andMM/MC, CD, Radio, Tape 1,

Tape 2 inputs and tape outputphono sockets mounted on anisolated input panel to eliminateeddy current effects in theamplifier chassis.A solder resist and a compo-nent legend on the pcb simplifyassembly. Inputs are connecteddirectly to the selector switchand not routed across anunscreened pcb or subject tomultiple stages of potentiallyunreliable switch contacts (as iscommon with some designs).All resistors are 1% metal filmand film capacitors are usedwherever possible.An earth plane on the pcb aidssonic performance by screen-ing sensitive components andsignal tracks and also allows anideal power supply star feedand earth return network. Thefully stabilised supply has noripple. Other designs requireover complicated prearnpstages to increase ripple rejec-tion. Removal of the cause ofthe ripple is a more elegantsolution.

Specification and design philosophyInputs Phono MM, 2mV into 47K. Input overload 60mV (29d8).

Phono MC, 300gV into 470 ohms. Input overload 9mV (29dB).Radio, Tape 1, Tape 2, 50mV into 100K. Input overload 2V (32dB).CD, 200mV into 10K. Input overload 8V (32dB).

All voltages are RMS, all sensitivities refer to 40 watts output at 1kHz.

S+ N ratios .Phono MM ref 5mV input, 80dB, (input terminated into 1K).Phono MC ref 5000/ input, 70dB, (input terminated into 330 ohms).Line inputs ref 100mV input, 85dB, (input terminated into 10K).

All noise figures are unweighted RMS 20Hz - 20kHz bandwidth. They are a direct measure of theoutput noise when the volume control is set to obtain 40 watts output into 8 ohms from the statedreference input level.

Controls ....6 position Input Selector.Volume, Low Lift, Tone Cancel, Balance, Bass, Treble.MM/MC selector on rear panel.Mains on/off, green LED on indicator.

Features ....Passive RIAA equalisation and low insertion loss tone control stage.Dual action volume control for optimum signal overhead and signal to noise ratio.Fully regulated DC supply to all stages including output stage.Rugged TO3 complementary Darlington output and PSU transistors.High current design. Star earthing arrangement.Automatic switch on delay.Simple construction, comprehensive instructions.Double sided PCB with solder resist and component overlay. Earth plane top layerconsiderably reduces component interaction.

Outputs 40 + 40 watts into 8 ohms. 80 watts into 4 ohms.Buffered Tape Output, 200mV nominal.

Functions ...Treble range +/-5dB at 12kHz. Bass range +/- 5dB at 60Hz.Infra cut facility on phono inputs, -6dB at 10HzLow lift maximum of -3dB at 30Hz, user definable at build stage.

Dimensions .440w x 240d x 85h mm.

The outer case has a high qual-ity black gloss finish and theseparate front panel is printedin gloss white. All metalwork isready drilled and the appear-ance and performance of thefully built amplifier will makeall constructors proud of theirwork.The sonic ability of the ampli-fier is quite superb, the sound isdetailed, articulate yet not overclinical. Dynamics are pro-duced with a bite that bringsgood recordings alive. Unfortu-nately, poor recordings arequite likely to sound evenworse! In this case, the tonecontrols can help.

Gatehouse Audio105 High StreetEVESHAMWorcestershire WRll 4EBTelephone: (0386) 98873

2 SUPPLEMENT

13 Editorial14 News from the world of electronics19 Mobile satcoms for the future: Dr Norbury

of the Rutherford Appleton Laboratory ex-plains the advantages of a highly ellipticalorbit for communications satellites over ageostationary position.

22 Solar power generation: many of us wouldlike to see a real alternative to nuclear and oilor coal burning power stations. Solar energywhich is freely available and in plentifulsupply is, therefore, taking on new import-ance.

27 Lasers: an overview. Since the first lasersappeared in the early 1960s, they have be-come indispensable in such diverse appli-cations as fibre optic communications,surgery, compact disc players and theStrategic Defence Initiative.

32 The MAC system: the European Broad-casting Union-EBU-has adopted a newfamily of television standards called MAC-multiplexed analogue components-developedby the Independent Broadcasting Authority.This article explains the aims of the newsystem.

Solar power generationfx 22

The compact discp. 39

The MAC systemp. 32

39 The compact disc: an introduction to thedevelopment of the CD, how it is made; theoptical system in the CD player; commercialaspects of CD. The article finishes with abrief survey of the products of 20 of the best-known makers of CD players.

46 Telecommunications: news from the worldof the new telecommunications.

50 Filters: theory and practice -1. Although agreat many filters are nowadays availableready made at reasonable prices, there remainoccasions when one has to be designed fromscratch. In this first part of a three-partarticle, A.B. Bradshaw looks at the theoryunderlying such design.

54 Where students make their own chips:the University of Dundee gets its electronicsengineering graduates to design and make in-tegrated circuits in their own laboratory.

56 ATN Filmnet decoder: an update on ourMay article in view of the change in ATN'sscrambling system.

SUPPLEMENT OF DESIGNPROJECTS Opp. page 38

INFORMATION57 Corrections; 58 New products; 64 Readers' services; 66 Terms of business.

GUIDE LINES69 Switchboard; 72 Buyers guide; 74 Classified ads; 74 Index of advertisers.

July/August '1987Volume 13Number 147

In our Septemberissue: Horn loading

revisited CMOS-RAM for

C64 The positive

impedance con-verter

Testing the instru-ments oftomorrow

Recording/playbackamplifier

SSB adapter

The visible fluor-escence from adoped single -modeoptical fibre illus-trates its potentialas a low-cost laserwith possible appli-cations in trans-mission systems andas temperature andliquid sensors. TheOptical Fibre Groupat Southampton Uni-versity is believed tobe the first organiz-ation to develop adoped optical fibrethat can be used inthis way. Normally,such materialcauses large op-tical losses, but thegroup has found away to ensure thatthe new fibre's trans-mission is just asgood as that inconventional tele-communicationsfibre.

EE

July AL:gos: 19B7

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ELECTRONIC GUARD DOG KITOne of the best deterrents to a burglar is a guarddog and 11w new kit provides the barking with-out the late! The kit when assembled can beconnected to a doorbell. pressure mat or anyother intruder detector and wel proder:e 3 ran-: -on series of threatening barks mi. -. the

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DISCO LIGHTING KITSDL1CCOK - Tide value -for -money 4 -way chaserfeatures bidirectional sequence and dimming.1kAY per channel E17.5010121000K -A loner cost uni deectional ye -r -Se -I of the aboyw Zero switching to reduce inter.rceence. E9.85DLA/1 DL Er 131271033K) Optima/ opto input

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WAY SEQUENCER KITDON'T CHASE AROUND FORANOTHER SEQUENCERThe oLa...-)3K, on 8 easy sequencer kit erdh!: uift n Opt0 hsofated sound to fold inputMuch comm complete :h a pre.-:Doran-meet EPROM conta. - EGHTY* ES 80. different sequences - stanlard flashing and chase Muth:: KIT in-lodes full Histructrons and a -r-ayanents-ken the PCB connectors! a,-: -a:Jae; onlybras and 3 control knob ro - : ere Other

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VERSATILE REMOTECONTROL KIT

This kit inaudesall components1+ transformer)to make a sersi-live IR receiverwith 16 logic out-puts (0-15V1 which with suitable interface cir-cuitry (relays lilacs, etc - details supplied.can be used to switch up to 16 items c'equipment on or off remotely. The outputsmay be latched Ito the last received code'or momentary fon during transmission) tr,specifying the decoder IC and a isy stabslied supply is available to pewee externscircuits.Supply: 240V AC or 15-24V DC at 10mA.Size lexeluchng transformer) 9 x 4 x 2crnsThe companion transmitter is the MK1Ewhkh operates horn a 9V PP3 battery ansgives a range of up to 60ft. Two keyboardsare available MK9 (4 -way) and MK17.06 -way/, depending on the number of out-puts to be used.MK12 IR Receiver (incl. transformer) 114.85M K18 TransmitterMK9 4 -Way Keyboard 12.00MK10 I6 -Way Keyboard E6_95601 133 Box for Transmitter E2.60

-.,any componentsar designed to re-p -a:: z _ _ z z switch and control ur..to : -TO R:KOK Remote Control Dimmer. £16.451,) K6 Transmitter for above .... E4.95TD300K Touchdimmer E8.50TS300K Touchswitch (8.50TDE/K Exterd6on kit for 2 -way

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AUDIOPHILE QUALITY AMPLIFIER KITThe advent of the GATE ONE amplifier kit gives all electronics and Hi-Fi enthusiaststhe opportunity of building a top quality professionally engineered amplifier. Thedesign incorporates a host of features common to most mid -range ready builtamplifiers combined with various aspects of design normally associated with moreesoteric products.Features include 40+40 watt output, rasive RIAA and tone equalisation, high cur-rent output and fully regulated supply, double sided earth plane pcb, metal filmresistors, superb sonic performance, professionally finished case. The kit is E161.00,a fully built version is £201.25 inc. Send for further details to:GATEHOUSE AUDIO, 105 HIGH STREET, EVESHAM, WORCS. 1.YR11

MNI ELECTRONICSWe stock a wide range of components:transformers, switches, pots, ICs, capacitors, resistors, diodes,boxes, triacs, LEDs, cable, connectors, PCBs -in fact, all you need for your projects.

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Managing Editor: Len SeymourTechnical Editor: J SuitingAdvertisement manager: S BrooksEditorial offices:Steadfast HouseBath PlaceHigh Street. BarnetHerts EN5 5XETelephone:Editorial (UK): 01-441 WA

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Elektor Verlag GmbHStIsterfeld-Strafe 255100 Aachen - West GermanyEditor: E J A KrempelsauerBektor EPEKeraiskaki 1416673 Voula - Athens - GreeceEditor: E XanthoulisElektor Electronics PVT Ltd.Chhotani Building52 C, Proctor Road, Grant Road (ElBombay 400 007 - IndiaEditor: Surendra lyerElektuur B.V.Peter Treckpoetstraat 2-46191 VK Beek -- the NetherlandsEditor: P E L KersemakersFerreira 5 Bento Ida.R.D. Estefania, 32-1"1000 Lisboa - PortugalEditor: Jorge GoncelvesIngelek S.A.Plaza Republica Ecuador2-28016 Madrid - SpainEditor: A M FerrerIn part:Kedhorn Holdings PTY LtdCnr Fox Valley Road EtKiogle StreetWahroonga NSW 2076 - AustraliaEditor: Roger HarrisonElectronic Press ABBox 63182 11 Danderyd - SwedenEditor: Bill CedrumInternational co-ordinatingEt technical manager:K S M WalravenInternational editorial secretariat:G W P v Linden; M Pardo

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Copyright c' 1987 Elektuur B.V.

ABC

tAugust 1987

R&D funding in BritainMuch has been said and written in recent years about the decline ofBritish science, the lack of funds for research programmes, and the newbrain drain. But is R&D funding in Britain really as poor as depicted bymany?

In 1981, Japan launched a ten-year national programme to developwhat are known as fifth generation computer systems. This ambitious proj-ect aims to bring together the necessary elements of clever computerswhich, in the 1990s, will be able to demonstrate artificial intelligenceand simulate human hearing, speech, and vision.

Britain's response to this challenge was to mount its own advancedresearch programme. Known as the Alvey Programme, it was started in1983, and will eventually cost about £350 million, of which £200 millionwill come from public funds, and the remainder from participatingcompanies.

The Alvey Programme consists of pre -competitive research projects whichfit into national strategies in important areas of technology. These involvecollaboration between universities, industry, and research establishments;and between different industrial companies.

At about the same time, the European Economic Community, also fearfulof lagging behind Japanese and American research, started a similarprogramme. This is known as ESPRIT (European Programme of Researchand Development in Information Technology). Again, collaboration be-tween companies and universities is a major feature of ESPRIT. The pro-gramme, in which many British companies and universities are involved,is funded on a fifty-fifty basis by the European Community and the par-ticipating industrial firms.

Another programme, started in 1985, is EUREKA (European Research Coor-dinating Agency), which is aimed at promoting collaboration instead ofcompetition between Europe's research and development organizations.Already, the amount of money committed to research projects under theEUREKA aegis exceeds £2,000 million. More than 100 projects havealready been started, in 41 of which British firms and universities are in-volved. This involvement will cost the British Government about £40 millionover the first five years.

A recent OECD report shows that of western nations Britain allocates abigger share of public spending to research than the United States,Federal Germany, or Japan; only France devotes more. If this were thewhole picture, all would be well. Unfortunately, when it comes to grossexpenditure on R&D, Britain lags behind all other western industrialnations.

This is not the direct fault of the government, but rather because British in-dustry's spending on R&D has fallen way behind that of other countriessince the 1960s. In the intervening period, real spending on R&D by theindustry in the USA, Federal Germany, and France has doubled, while ithas trebled in Japan. In Britain, it has increased by just about 20% overthe same period.

British industry may well need government help in the form of, for in-stance, a high rate of tax relief on R&D spending, or grants for particularresearch programmes, but it would appear highly beneficial if it and itsbackers, the commercial banks, would forgo their current short-termoutlook and adopt a long-term strategy as regards R&D funding.

p-VaiR&_:q.azi Ore 4-1.01..r.7-CNS

EE

July 'August 198714

World's fastestintegrated cir-cuit claimedA world speed record for inte-grated circuits of 18 GHz is be-ing claimed by HughesResearch Laboratories inMalibu, California. The galliumarsenide chip can divide bytwo, a basic processing func-tion, 18 billion times a second -said to be five times faster thancommercially available GaAsintegrated circuits and tentimes faster than commercialsilicon chips.The new digital circuit willmake it possible to raise theprocessing speed and reducethe cost of information handlingfor the next generation of digitalcommunications and signal -processing equipment, sayHughes scientists. Applicationscould include optical -fibrecommunications links, super-computers, advanced radarsand communications satellites.

In Fig. 1 three of the chips arepictured alongside the eye of aneedle.The device incorporates novel

"airbridges", elevated connec-tors that link the logic gates onthe chip (seen in Fig. 2 wherethe white line at bottom right in-dicates 10 µM). The airbridgesminimize the capacitive loadingof the interconnections andkeep energy losses to a mini-mum.

Canon andNationalSemiconductorto cooperateon develop-ment of laserbeam printersCanon Inc. and National Semi-conductor Corporation have an-nounced their intent to coop-erate on the definition and de-velopment of integrated circuitsand software for products to bemanufactured and marketed byCanon. The first productresulting from the agreementwill be a laser -beam printer.The printer market is one focusfor National's Series 32000 fam-ily of 32 -bit microprocessorproducts. Although the inte-grated circuits and softwaredeveloped are initially in-tended for laser -beam printers,the companies will explore abroadening of the relationshipin the future.

IBM licensesMicro FocusCOBOLIBM has licensed Micro FocusCOBOL for the new IBM Per-sonal System/2 range of com-puters, running IBM OperatingSystem/2, and for its existingIBM Personal Computer range.The newly announced IBMCOBOL/2 has an early releasecalled IBM COBOL Version2.00, which supports IBM DOSVersion 3.2 and 3.3. Users ofIBM COBOL Version 2.00 willbe upgraded by IBM to IBMCOBOL when OS/2 becomesgenerally available.IBM COBOL/2 is an ANSI '85compiler with a built-in inter-active debugger that can run onboth IBM DOS 3.3 or IBM Oper-ating System/2. It is ideal forexisting applications from otherenvironments and for develop-ing new high-speed, high -quality business applications.IBM COBOL/2 generates stan-dard object module formatwhich is linkable with otherlanguages and which providesmulti-user support across theIBM PC Network. The widerange of supported COBOLsyntax includes ANSI '85 In-termediate Level COBOL, ANSI'74 High Level COBOL, a subsetof IBM VS COBOL Version 1.00and Micro Focus extensions ofthe IBM Personal Computer.IBM's Systems ApplicationArchitecture (SAA), announcedlast March by IBM, defines astandard for cross -systems com-patibility. IBM COBOL/2 meetsIBM's SAA standards, providinga mechanism for COBOL appli-cations to migrate across theIBM product line. This is IBM'sfirst announcement of a COBOLimplementation which willmeet IBM's SAA standard.

Factron winskey ATLAS orderFactron Schlumberger has justwon a major order for ATLAScompilation facilities from the

UK's Ministry of Defence. Theorder calls for an ATLAS com-piler with a post -processor forMEDIATOR, Factron's own testlanguage. The compiler will beused by the Royal Air Force(RAF) for writing test programsfor avionics equipment.The order signals a major trendwithin the UK's defenceministry away from purchasing'special -to -type' test systems,towards general-purpose auto-matic test equipment (GPATE).ATLAS, in conjunction with theuse of GPATE, provides themeans for major savings in testsystem and software costs,allowing test software to be'transported' across a range ofdifferent test systems from dif-ferent manufacturers. A testprogram will now only need tobe written once during a prod-uct's lifetime, and will be able torun on any new test system theRAF obtains.

Newbury Dataawarded forproductioninnovationNewbury Data Recording Ltdhas won the "Productivity En-hancement in Electronics"category of the ProductionInnovation in Electronics (PIE)Award for 1987.Newbury won this importantcategory of the award againststrong competition from RankXerox, ICI Chemicals andPolymer Group, Kerry Ultra-sonics, Marconi Instruments,BICC Data Network and Lucas,for its use of state of the art Sur-face Mount manufacturing tech-niques to provide a significantand competitive gain in thetechnically exacting disc driveproduction environment.The Surface Mount System isused at the company's 330,000square ft manufacturing plant atWinsford, Cheshire. It consistsof fully automated printed cir-cuit board assembly modulessupplied by Manix (UK) Ltd.

es

NEWS NEWS NEWS NEWS NE*PEOPLE

Brian Loader, BSc (Eng),MIEE., C.Eng., has been ap-pointed director of navalbusiness at Marconi RadarSystems CHELMSFORD.

PAL Components have an-nounced the following promo-tions and appointments. DerekNewport (see photograph)

becomes Development Direc-tor, with Eric Vavasour takingthe post of Technical Manager.

Martin Fray (see photograph)is appointed Director andGeneral Manager and DavidKnowles becomes Manufactur-ing Manager.

Geoff Potts has joined SentryTest Systems, part ofSchlumberger's CAS group ofcompanies and a world leaderin the ATE market, as UKManager.

Toby Warson has been named

vice president and managingdirector of Honeywell Limitedin the UK. He succeeds Dr JimMcGregor, who retired lastMarch.

ERA Technology Ltd have an-nounced the following the fol-lowing appointments: RichardStokes, MSc, CEng, FLEE, andDr Martin Desvaux becomeExecutive Directors of thecompany. jack Donald, BSc,CEng, CDip AF, becomes anAssociate Director, and Dr NeilWilliams becomes Manager ofthe company's Radio Fre-quency Technology Division.

ATE Systems International hasannounced the appointment ofJohn Amos of Amos -Mitchell &Associates of ONTARIO as theirnew Canadian representatives.

High Technology Electronicshas appointed Rex Hanson astelecomms business manager,and Brian Petty as major ac-counts manager to spearhead anew push into the telecom-munications end -user market.

GrampianAmateurComputerSocietyThe Grampian Amateur Com-puter Society was formed aboutten years ago. Its memberscome from all walks of life, areof all ages, and possess a var-iety of machines and a variety ofinterests. Although it is anamateur society, great stress isplaced on the more serious ap-plications of the computer andon the computer itself, as op-posed to games.The society holds regularmeetings on Monday evenings.These meetings aim at pro-viding organized talks, demon-strations, and visits wheneverpossible. There is a two -

monthly newsletter which givesdetails of forthcoming events.Further information from PaulCuthbertson at 18 MorningsideCrescent o Blackhall o IN-VERURIE ABS 9FA o tele-phone (0467) 29030, or fromBruce Edelsten at (0224) 639911.

Marconi forLondon CityAirportMarconi Command and ControlSystems of Leicester has re-ceived an order from LondonCity Airport Ltd for the supplyof a two field site instrumentedvisual range and meteorologi-cal system for the new STOL-port at Newham in the heart ofLondon's dockland.The system will provide METAR(Meteorological Area Report)data in serial format for theAeronautical Fixed Telecom-munication Network as well aslocal displays.These new facilities are to beinstalled by Marconi to enablethe airport to commence oper-ation in October 1987. The air-port will be handling up to 120aircraft movements per week-day and has been designed fora capacity of up to 1.2 millionpassengers a year mainlytravelling within a 400 mileradius in one of the world's big-gest markets for businesstravellers.

London's disused docklands are coming alive again. A huge areaof more than 2000 hectares (about 5000 acres) just down riverfrom Tower Bridge is being transformed into an exciting place forLondoners to live, work, and enjoy themselves. The mostdramatic development will be a Stoloon - a short take off andlanding airport - between the Royal Albert and King Georg Vdocks. This will be serviced by quiet De Havilland Dash Seventurboprop airliners to provide City businessmen with convenientservices to mainland Europe and other British cities. Seen in thephotograph are new office blocks and high technologyworkshops.

EE

July/August 198716

NEWS NEWS NEWS NEWS NEW1

Three-way racefor diamondthin filmDuring the thirty years prior to1977, it began to dawn onvarious members of theworldwide scientific communi-ty that synthetic diamondmaterial might possibly bemade in thin-film form, usingchemical vapor deposition(CVD) techniques, says an IRDreport. Important early workwas done by Angus et al at CaseWestern Reserve in the U.S. andby Derjaguin et al at the Insti-tute for Physical Chemistry(Moscow). A 1977 paper by Der-jaguin might have been thematch which ignited worldwidecompetition (mostly betweenJapan, the USSR and the U.S.) forthe achievement of commer-cially viable processes formanufacturing diamond thinfilm. According to IRD, thereason for the excitement overthis technology, which is now atthe very early stages of com-mercialization, is that diamondfilm possesses unique mechan-ical, electronic and opticalproperties, which have ap-plicability in a wide range ofmilitary and commercialmarkets. For example, it seemsthat Diamond Thin Film (DTF)chips will be superior in speedand in environmental resistanceproperties to Gallium Arsenide.Coatings for lenses andradomes can be made verystrong and, at the same time,

transparent to infra -red andmicrowave radiation.Worldwide activities in dia-mond thin film are still largelyfocused on research and devel-opment, although commercialpayoff of many of these ac-tivities is now in sight, accord-ing to Diamond thin film: thethreshold of commercialization(#733), a new study from Inter-national Resource Devel-opment.In the U.S., IBM scientists havebeen investigating diamondfilms for at least three years,says the IRD report, whichsuggests that IBM's YorktownHeights research facility is in-creasing its efforts in this area.Start-up company Crystallume(Palo Alto, CA) may chip its firstdiamond film products this yearor next. But in Japan, diamondfilmcoated knives for electronmicroscopy are already beingshipped by Shinetsu ChemicalCompany, and Sony ismarketing a loudspeakertweeter which uses diamondfilm. Sumitomo is expected tosoon be releasing its first dia-mond film -based chips for ap-plications involving hostileenvironmental conditions (suchas in spacecraft or automobileengines).

ITT InstrumentappointmentITT Instruments, whose prod-

PlAroun THIN FUN HORIDWIDE PROSPECTIVE comicial_

SEAETS FOR SEIECTED PRODUCTS

(S MILLION)

1987 1520 1995

LOUDSPEAKERS S 5 $ 30 S 50

COATED TOOLS/KNIVES 10 40 150

LENS/WINDOW COATINGS 2 1,43 70

OPTICAL DISK COATINGS 5 70

UV LASER COATINGS 25

CIEtERCIALAICONDUCTORS 5 400

TOTAL' S17 5120 5765

FOR THESE MARKETS ONLY; THIS IS HOT A COMPREHENSIVE LIST OFDIAMOND THIN-FILM APPLICATIONS.

ucts include oscilloscopes,multimeters and related ge-neral purpose test & measure-ment equipment, has appointedthe newly created Test &

Measurement Division of Feed-back Instruments Ltd. as its firstUK distributor.

Products covered by the newagreement include realtimeand digital -storage oscillo-scopes, and bench power sup-plies in addition to the estab-lished digital and analoguemultimeter range. Most of theproduct range is manufacturedat ITT's plant in Annecy, France,and marketed in the UK via therecently established ITT Instru-ments operation at Slough,Berks.Feedback Instruments has astrong market base in theeducational and researchmarkets, resulting from manyyears' experience in supplyingits own manufactured productsto these markets - and it is nowexpanding on this success byadding other companies' prod-ucts to its range via its new Test& Measurement Division.Photographed after the signingof the agreement are (left toright): Peter Rummer, GeneralManager of ITT Instruments inthe UK, and Tony Morris, Feed-back's Test & Measurement Div-ision Manager.

Light -showmultiscanA laser graphics/effects con-troller developed by Laserpoint

Ltd. of Cambridge can projectbeams, patterns, words, pic-tures, logos and animated se-quences. It is claimed to be thefirst capable of presenting acomplete light show by con-trolling both laser -effects out-put and other effects deviceswithin a room.With the 'MultiScan' system, ac-cording to Laserpoint, it is poss-ible to involve the whole activearea of a venue with amemorable lighting and laserspectacle.

The projection unit (effectshead) is particularly suitable foran argon -ion laser and/or akrypton -ion laser. Respectivelyemitting blue/green and redlight these will, when com-bined, produce a full range ofcolours including white light. Inthe projection unit are a pair ofXY scanners and a prism as-sembly which is used for coloursection.An interface with its ownseparate microprocessor linksthe effects from the MultiScanto the motion of remote reflec-tors. Further options includedisk storage of effects, tapecontrol for preprogrammed se-quences, a digitiser for enter-ing artwork, and anoscilloscope output monitorpermitting complex sequencesto beset up without the lasersource being switched.

New Franchisefor BraburyBrabury Limited has been ap-pointed international distributorfor the full range of televisiontest -chart products manufac-tured by Porta-Pattern Inc. ofLos Angeles. The tradingagreement between the twoCompanies gives Brabury theexclusive franchise for sales ofthese products in mostcountries outside the Americancontinents.

1111 EE

July/August 1987

NEWS NEWS NEWS NEWS NEVEVENTS

The Electronics Publishing &Print Show will be held in Lon-don from 29 June to 2 July.Further information fromOnline International Ltd o

Pinner Green House o AshHill Drive o PINNER HAS 2AEo telephone 01-868 4466.

The Light and Sound Show willbe held at the Novotel Hotel inLondon (W6) from 30 August to2 September. Further infor-mation from ProfessionalLighting and Sound Associ-ation o 1 West Ruislip Stationo RUISLIP HA4 7DW o tele-phone (08956) 34515.

Multivariable control for in-dustrial applications from 5-10July at the University ofStrathclyde. Glasgow.History of Electrical Engineer-ing from 10-13 July at Trinity Col-lege, Dublin.Computer -aided tools for VLSIsystems from 19-24 July atUniversity of Lancaster.Transmission for Telecom-munications from 19-24 July atthe University of Ashton.Satellite communicationsystems from 26-31 July at theUniversity of Surrey.Software engineering for mi-croprocessor systems in July.Radio frequency techniques atthe University of Bradford dur-ing the summer.Details of the above vacationschools may be obtained fromThe Secretary, IEE o SavoyPlace o LONDON WC2R OBLa telephone 01-240 7735

Fibre optic communicationsystems and application areasat the Caransa Crest Hotel,Amsterdam, 13-15 July.Microelectronics packaging atthe Crest Hotel, Amsterdam,14-17 July.

Microelectronics interconnec-tion and surface mounting atthe Crest Hotel, Amsterdam,2024 July.Information about thesecourses may be obtained fromAnne Thomas at the Centre forProfessional Advancement oPalestrinastraat 1 a 1071 LCAMSTERDAM c telephone(020) 623050.

1987 Innovationcompetitionprize winnersannouncedDr Anthony Barker, a MedicalPhysicist at the Royal Hallam -shire Hospital, Sheffield, hasbeen announced as the 1987winner of the IEE Prize for Inno-vation Competition. Dr Barkerwon the award for his develop-ment of a magnetic nervestimulator for use in the diag-nosis of disorders of the centraland peripheral nervous system(see Elektor Electronics, June1987, p. 26).

MP forWokinghamopens newPrintronix UKheadquartersConservative MP for Wok -Ingham, Sir W Van Straubenzeerecently opened the new UKheadquarters of Printronix Ltd.,a subsidiary of Printronix Inc.,the third largest computerprinter manufacturer in theUnited States.Occupying part of the LoddonVale Centre in Woodley nearReading, Printronix have nowmoved from their temporarybase in Wrexham to be closerto their main OEM businessclients in the South East.

The new offices in Woodley in-clude a comprehensive demon-stration facility, available foruse by sales personnel ofPragma and the distributors ofPrintronix non-exclusive prod-ucts sold through Keytech inthe north of England and Riva inthe south.Seen in the picture are Sir WVan Straubenzee (centre) with athis left Wendy Lindley, PA to theManaging Director. Other Prin-tronix staff in the picture are:Martin Phillips, Sales Manager(left), and John King, Accoun-tant (right).

HawkerSiddeley buysanother US in-strumentcompanyHawker Siddeley, the London-based international electricaland mechanical engineeringgroup, has bought Modutec Incin the US from Thorn EMI for£5.1 million in cash. It is thefourth US company acquired bythe group this year.Modutec, which will retain itsdistinct identity, is the US'sleading supplier of analogueand digital panel meters.Customers include manufac-turers of power generation anddistribution, process controland portable electronic equip-ment. Based in Norwalk, Con-necticut, Modutec also has

manufacturing sites in NewHampshire, Pennsylvania andBarbados.The acquisition of Modutecmarks a further expansion ofHawker Siddeley's control andinstrumentation activities,which include the manufactureand supply of electrical in-dicating instruments, electroniccontrol and protection prod-ucts, sensors and poten-tiometers and advanced dataacquisition and control systems.The Modutec purchase followsthe acquisition of Metermasterin January (US$9.8 million) andFlight Accessory Services(USS6.0 million) in March.

HTE acquiredby venturecapitalcompanyHTE (High Technology Elec-tronics Limited) has been ac-quired in a ELI million deal byAlan Patricof Associates (APA),the venture capital arm of theMMG Patricof Group plc.HTE supplies computer -basedequipment for a wide range ofmarket sectors, including pro-cess control, telecommuni-cations, city informationsystems, defence and broad-casting. Started up in 1979 andpurchased a year later by GrandMetropolitan, the company hasmaintained an impressivegrowth rate and is nowrecognised as a market leaderwith a current turnover around£5 million.Immediate plans for thecompany include extensive in-vestment to broaden the prod-uct base and address newmarkets. Further penetration ofthe UK and European telecomsmarkets are early objectives.An expanded product line insystems level and finishedproducts, with new emphasison distribution and addedvalue, is set to yield a projectedannual growth rate of 40% forthe next four years.

EE

July/August 198718

NEWS NEWS NEWS NEWS NEWManagementbuys Norwichcapacitor div-ision from STCA team of senior managers hasacquired the Norwich -basedcomponents division of STC,the international electronicsgroup, with financial supportfrom institutional investors ledby the Cambridge office of 3i,Investors in Industry.The other major institutional in-vestor supporting the buyout isCIN Industrial Investments,while substantial bankingfacilities have been provided byBarclays Bank.The company, which has beenrenamed Syfer Technology Ltd,specialises in the manufactureof multilayer ceramic capaci-tors - small components madeup of layers of conductiveprecious metals and ceramic in-sulator. The capacitors are usedmainly in computer memorieswhere they store the energyneeded to allow the RandomAccess Memory (RAM) to func-tion. About a quarter of thecompany's sales go abroad.

Complex chipspromise betterTV picturesTwo Very Large Scale Inte-gration (VLSI) silicon chips, de-signed by a group of ninefinal -year students at Kent Uni-versity could lead to theelimination of fuzzy pictures ontelevision screens and crackl-ing interference on telephones.These are the firstundergraduate chip designs tobe carried out with the facilitiesof Kent's recently establishedElectronic Computer -AidedDesign (ECAD) Laboratory. Kentis one of the few universities inthe UK where students canundertake this kind of work.Graduates of this degree pro-gramme are in much demandby industry.Each chip, which measures a

mere 3 mm by 4 mm, contains15,000 transistors. The studentsbegan their project in October1986 and completed it in fourmonths on schedule in January.The design of a 15,000 transistorchip requires powerful designtools. The work was carried outon the Apollo Workstations inthe ECAD Laboratory with a var-iety of software tools, some ofwhich were designed in Kent,the rest provided by industrialpartners.The students' chips are at pres-ent being fabricated byEuropean Silicon Structures Ltdon their Californian productionline. Their designs will bedeveloped by members of theDigital Systems Group at Kent'sElectronic EngineeringLaboratory with a view to amarketable product beingproduced.

Industrialcomputer salesin WesternEuropeOwing to the decline in theEuropean data processingmarket, large computer firmsare forced to look outside officeautomation for growth-and in-

dustry is where they will beturning, according to Com-puters in the Industrial Environ-ment in Europe (#E893), a newreport from Frost & Sullivan.The study claims that FederalGermany will remain largest innational sales volume, followedby the UK. The French em-phasis on communications inthe computer field is somewhatmarginal to mainstream in-dustrial computers.Industrial computer sales inWestern Europe amounted to$751 million in 1986, and theyare likely to reach $897 millionby 1991 (in constant 1986 dol-lars). If expressed in units. themarket is growing faster-from22.000 to 61,000 over the sameperiod. This is because a highproportion of the installationswill be small systems. andbecause the current averageselling price of most systems(hardware only) of 533,000 willhave dropped to less than$15,000 by 1991.

A.F. Bulgin ft Co PLC have appointed Orbitec as their officialrepresentatives for France. Seen in the picture are Orbitec'sMademoiselle Isolde Jenal (centre) and Monsieur Larrouy (2ndfrom right) during a tour of Bulgin's Barking ,factory. Also seenare Bulgin Chairman, Ronald Bulgin (3rd from left), DavidHarrington (2nd left), Sales Er Marketing Director, and SteveChapman (extreme right, Works Director.

StandalonePoint of Salewins Marks andSpencerbusinessTHORN EMI Micrologic has re-ceived a major order fromMarks and Spencer PLC for itsStandalone Point of Sale systems(SPOS). The order follows a suc-cessful pilot of 300 terminals,which took place in nine storesduring the peak Christmasshopping period. The order toequip a further fifty stores is for1400 sales points to be installedby September this year and isvalued at f3.7M. This order ispart of Marks and Spencer'soverall plan to install POSsystems in all their stores dur-ing 1988. The system is part ofTHORN EMI Micrologic's TEM2000 product range.Details of each day's trading arerecorded at each sales pointonto a CMOS cartridge, whichis removed from the control unitat the end of the day, or as re-quired. It is plugged into amultiple memory unit (MMU)along with the cartridges fromall the other sales points withinthe store.The MMU, also designed anddeveloped by THORN EMIMicrologic, is polled by an in-store computer which collatesall the transaction data beforetransmitting it during the night,using the public switch net-work, to Marks and Spencer'sown central computer facility.Updated prices, productchanges and credit card infor-mation are then transmitted tothe MMUs, in each store for thefollowing day's trading.

19 EE

July/August 1987

MOBILE SATCOMSFOR THE FUTURE

by Dr John R. Norbury, Rutherford Appleton Laboratory

We have come to regard the geostationary satellite as the normfor communication between fixed stations and mobile stationssuch as ships and aircraft. Recent studies show the advantages

of a highly elliptical orbit when planning satellitecommunications with land -based mobile stations, offering much

better coverage at higher latitudes.

Nearly all recent proposals forsatellite communications sys-tems to provide a service tomobile stations have commonfeatures. They include the useof geostationary satellites,operating at radio frequenciesaround 900 MHz or 1.5 GHz;either low -gain omnidirectionalantennas or higher -gain steer -able directional antennas forthe mobile terminals; and com-munication on narrow fre-quency bands which permitsonly a single channel to be car-ried on each allocated fre-quency (known as singlechannel per carrier, or SCPC,access techniques, whichmeans restriction of data trans-mission rates to the low figureof some 16 kilobit s-').Communication via geostation-ary satellites gives globalcoverage from a threesatelliteconstellation, which is ideal formost maritime and aeronauticalapplications, but it suffers fromsomewhat severe propagationproblems when the line -of -sightpath from the ground station tothe satellite is at a moderateangle of elevation. This is es-pecially so with land mobilesatellite services (LMSS), wherethe low angle may lead tomultipath propagation effects,attenuation by trees andblockage of the signal bybuildings or uneven terrain.These factors place con-siderable constraints on thetype of system that can beplanned. For land mobile sta-tions, there has to be a toler-ance of fading of the signalpower by a ratio of about 30:1,which in the communicationsengineer's parlance is a 15 dB(decibel) fading margin, to en-

sure a 90 per cent probability ofacceptable speech communi-cation over 90 per cent of theterrain covered in suburbanand rural areas of NorthAmerica.Europe, with its more northerlysituation and its mountainousterrain both in northern andsouthern regions, may need aneven greater margin if there isto be a good enough service.Cost considerations of landmobile stations call for simple,low-cost antennas; that in turnmeans the satellite should havea very large effective transmit-ter power to provide a serviceof commercial standard. Thiscriterion could be met by usinghigh -power transmitters andlarge satellite antennas, butonly at a considerable penaltyto the overall system cost.

The Molniya OrbitAn alternative to the geostation-ary orbit is the 12 -hour Molniya

orbit, used extensively by theSoviet Union and illustrated inthe first diagram. It is a highlyelliptical orbit which provides asatellite position giving anglesnear to that at zenith, whenviewed from Earth at moderatelatitudes, for eight hours of itsorbit time. On alternate orbits itprovides a further eight hoursfor a region at the same latitudebut 180 degrees different inlongitude. For 24 -hour coverageover one region means usingthree satellites in three orbitalplanes separated by 120 de-grees. Obviously, any such con-stellation of satellites also givescoverage for a region 180

degrees different in longitudefrom the originally plannedregion. Elevation angles forEurope and polar regionswould be high, as is shown bythe 'beam footprints' in the sec-ond diagram.The left-hand part of thediagram shows the view ofEarth from a satellite in aMolniya orbit with its apogee at

Fig. 1. The Molniya satellite orbit compared with thegeostationary (circular) orbit.

3.5°W. To the right is the viewfrom the equivalent geostation-ary position. coverage of thepolar region is seen to be ex-cellent using the Molniya orbit,in contrast to that provided bygeostationary orbit where theelevation angle to the satellite iszero at about 81 degrees Northor South. This means that to pro-vide complete polar coverage,even for fixed point-to-pointcommunications services, satel-lites in non-geostationary orbitsare needed.Several satellite configurationsare possible for LMSS, selectedto reduce the overall powerneeded in the satellite and,thereby, the overall system cost.Constellations of satellites inlow orbits have been proposedin the USA. and Canadian scien-tists have studied 12 and 24 -hour elliptical orbits in detail.British studies, published bythe UK Institution of ElectricalEngineers, have investigatedthe application of Molniyaorbits to provide UK coveragefor LMSS. Such systems haveseveral advantages for Europe.The elevation angles aregreater than 60 degrees andthere is the possibility of usinghigh -gain non-steerable anten-nas for the mobile stations.Furthermore, the reduction ofmultipath propagation withsuch an orbit adds to these fac-tors to remove many of the con-straints imposed by a geo-stationary orbit system. It meansthe fading margin that has to betolerated is reduced to a fewdecibels, and the gain of themobile station antenna could beas high as 15 dB, so the link canbe engineered taking into ac-count a starting advantage of

EE

July August 1987

some 100 times more antenna -to -antenna power being avail-able, from base station tomobile, than in the geostation-ary system. And, although it isnecessary to provide a three -satellite constellation forcoverage over 24 hours, thelaunch energy needed to placea satellite into a Molniya orbit isroughly half that for a geo-stationary equivalent.The capital cost of a satellitesystem tends to be relateddirectly to the amount of radio -frequency power needed forthe link. So any configurationthat reduces the power neededper voice channel, as in thecase of the elliptical orbit satel-lite, makes the system a greatdeal more commercially attract-ive. The provider of a satellitemobile service would have thechoice of an initial system ofsatellites working at relativelylow radio -frequency power pervoice channel, or have manymore revenue -earning channelsfor the same capital cost as in ageostationary system.Studies conducted recently inthe UK favour a 12 -hour ellip-tical orbit, because it would bethe lowest cost option for ademonstration satellite. But theorbit does pass through the VanAllen radiation belts, whichcould degrade electronics de-vices and solar panels. A so-called Tundra orbit, taking24 hours, enables this highradiation environment to beavoided. When deciding on thebest orbit for an operationalsystem, it will be necessary tocompare the threesatelliteMolniya constellation, using alow launch energy and smallsatellite antenna, with the two -satellite Tundra system where

20

Beam footprint for 1-5-rnantenna, L -band

Fig. 2. Comparison of coverage by (left) a Molniya orbit and (right) a geostationary orbit.

launch costs are higher, anten-nas are bigger but the radiationenvironment is better.

TransmissionFrequenciesProcedures for allocating fre-quencies for radio systems areco-ordinated through the Inter-national TelecommunicationUnion (ITU). Radio transmis-sions do not respect nationalboundaries, so agreeing usesof the radio spectrum tends tobe rather lengthy. A series ofWorld Administrative RadioConferences (WARC) are heldat suitable intervals to agree in-ternational usage. However, atthe last major conference,WARC 79, no pan of the spec-trum below 20 GHz was allo-cated to land mobile satelliteservices in the European re-gion (Region 1), whereas a smallallocation at UHF was allocated

Table

Members of a consortium of university -based and other laboratoriestaking part in the mobile payload study.

Member of consortium Area of study

Bradford UniversityKing's College, London UniversitySurrey University

Loughborough UniversityManchester UniversityPortsmouth PolytechnicQueen Mary College,London UniversityRutherford Appleton Laboratory

Mobile system; system designMicrowave systemOn -board processor!'system designModulation/demodulationCoding/decodingDoppler correctionAntenna

Co-ordinationisystem concepts

for use in the Americas (Region2) and Asia (Region 3).This lack of spectrum is a bigstumbling block for any com-mercial satellite land mobileservice. A special conference,WARC MOB 87, has been or-ganised to take place during1987 to tackle the problem.Several solutions seem poss-ible, with frequency slots in theregions of 1.5 GHz, 2.5 GHz and5 GHz being topics for dis-cussion. Although the con-ference might be mainly de-voted to considering geo-stationary systems, some atten-tion will also be given toelliptical orbit systems.

Payload StudyFor several years a universityconsortium in the UK, whosemembers are listed in the ac-companying table and whoseactivities are co-ordinated byRutherford Appleton Labora-tory, has been studying ad-vanced ideas for satellitecommunication systems underthe banner of CommunicationsEngineering Research Satellite(CERS). Two ideas that havegenerated considerable in-terest are the use of on -boardprocessing of signals in satellitesystems and the application ofthe Molniya orbit. This group isnow in the middle of a two-yearproject in which an electronicmodel of a mobile payload withfull on -board processing isbeing built.The design of the proposedpayload is outlined in the finaldiagram. A simple reflector of1.5 m diameter is planned for

the antenna, the necessarysteering to point to Earth in aMolniya orbit to be achieved bymanoeuvring the satellite. De-pending on the data rate, atransmitter power of between10 W and 20 W will be needed.Full demodulation and decod-ing of the received signalswould be included, using a var-iety of schemes. There areseveral modulation schemes tobe considered, including onein which the carrier is phase -shifted by the data keying pro-cess. Decoding would be poss-ible for a variety of codingschemes. An on -board micro-processor would control anelectronic buffer store to allowre -formatting of data and re-transmission using modulationand coding schemes that wouldbe independent of the up -linkchannel.Access schemes for communi-cation with the satellite are, first,time division multiplexing(TDM) on the down -link tomobile stations with time div-ision multiple access (TDMA)on the return path from mobilestation to satellite; second, TDMon the down -link to mobileswith SCPC on the up link. Thepayload, by using dual chan-nels for each system of access,allows full duplex (simul-taneous two-way) operation.Both up and down channelswould operate in the L -band (1.5to 1.6 GHz), with data rates of 64.128, 256 or 512 kilobit s-1.The motion of the satellite in theMolniya orbit causes a dopplershift in the transmitted and re-ceived signals. It is intended tocompensate for this on boardthe satellite by controlling the

111 EE

July/August 1987

3

Mobge-to-satelhte channels

Base station -to -satellitechannels

C)

Cr)

T-MUX

T MUX

Demod/Decode

41.Demod/Decode

Demod/Decode

On -boardprocessor

TDM/SCPC system

A'

2

_ad Mod/ le._

Encode

HPA

Demod/Decode

)

Variable clock rate

H Mod/Encode

TDIVUTDMA system (64. 128.256 Kbits/s)

Dopplercorrection

U

Fig. 3. Proposed scheme for the satellite -borne payload to be used for communication with mobile and base stations.

frequencies of its local oscil-lators, using either an on -boardcontrol system or ground con-trol.Different types of traffic such asshort, coded messages or voiceor facsimile could be accom-modated within the same timeframe merely by varying thelength of the time slot allocatedto each individual service bythe multiplexing system. Thefull capacity of the system,using 4.8 kilobit s-1 voicecoding would be about 50voice channels.For the mobile station, an anten-na with an angle of ± 15 de-grees could be used, mounted

on the vehicle roof with its axispointing vertically. Dimensionsof less than one metre squareare possible for this. The powerof the mobile transmitter wouldneed to be about 20 W. Theonly obstructions that may beexpected to impair receptionare overhead bridges or vegata-tion, or multipath scattering thatmight occur from very tallbuildings. System coverage, intime and space, would be bet-ter than 99 per cent.If the justification for satellitesystems to provide communi-cation with mobile stations isthat they would fill in all thegaps not covered by a terres-

trial -based cellular system, itmight be questionable whethera geostationary service will beattractive enough commerciallyat such a level of coverage. Anelliptical orbit system, althoughresorting to the complexity ofoperating a constellation ofsatellites, offers almost com-plete coverage even in urbanareas and at greatly reducedsignal strength requirement.Further spinoff might be foundif these ideas were implemen-ted in a European mobile sys-tem. The technology devel-oped could equally well be ap-plied to both mobile and fixedservice systems for the equa-

torial regions of the Earthoperating with a geostationarysatellite. If this mobile satellitesolution is commercially viablefor Europe, then the cost of thetransmitter -receiver, producedin quantity, would have to becomparable with those used interrestrial mobile systems,namely of the order of £1000.The potential for such tech-nology, in regions where satel-lite systems offer the mostpractical way of providing masscommunication, seems con-siderable.

OW PRODUCTS a NEW PRODUCTS NE'GMSVO7 singleboardcomputerGeneral Micro SystemsGMSVO7 advanced singleboard computer is now avail-able from UECS.This high-performance CPU forthe VMEbus provides ultra -highspeed data movement, deliv-ering the performance of aminicomputer at a fraction ofthe cost. Based on the 32 -bit68020 running at 20 MHz, itfeatures up to 1Mbyte no -wait -state RAM, optional advanced

lemory management and high-speed floating point maths. Areal-time clock calendar is stan-dard. Mezzanine options pro-vide VSB(MVMX32) compati-bility, as well as a wide range ofI/O possibilities. All systemconfiguration is software -controlled, minimising theneed for straps and jumpers.Universal Engineering andComputing Systems Ltd5-11 Tower StreetNewtonBIRMINGHAM B19 3UYTelephone: (021) 359 1749

(3630-16F)

EE

July/August 1987

SOLAR POWER GENERATION

Research and development info the use of solar energy as analternative source of energy have taken on new importance

since the oil crises of the 1970s. Moreover, many of us are afraidof the spread of nuclear power stations, and all of us want to get

rid of environmental pollution caused by oil or coal burningpower stations.

The sun converts 600 milliontons of hydrogen into heliumthrough nuclear fusion everysecond, and in the process re-leases enough energy to meetour earthly needs for a millionyears. Of course, only a tiny partof the solar energy falls ontoearth, which is readily seenwhen it is realized that the sunradiates equally in all direc-tions. Since the averagedistance from the sun to theearth is near enough 150 millionkilometres, the energy (in theform of electromagnetic radi-ation) takes about 8 minutes toreach the earth. In that time, thetotal energy radiated by the sunhas spread over the insideof a sphere of surface area3 x 10" km'. The total surfacearea of the earth that can be litby the sun at any one timeamounts to 113 x10' km'. Thismeans that only about 4 ten-thousandmillionth parts of the

totally radiated energy falls ontoearth. The rest is lost in theuniverse.The solar energy that reachesthe earth can be converted intoheat or electricity by variousmeans, mainly solar collectors,magneto -hydro -dynamic (MHD)generators, and photovoltaiccells (normally called solarcells).A major drawback to the wide-spread use of solar powergenerating systems is their highcost: at present, solar powercosts £5-20 per watt as com-pared with a few pence forcommercially produced elec-tricity. On the other hand, solarpower generation has a numberof important advantages:

Solar energy is free and inplentiful supply.

Electricity can be generated,directly or indirectly, where

it is needed, which in many

cases would obviate the needfor a distribution transmissionline system. In the case of most solar

power generating systems,there are no moving parts,which simplifies maintenanceand enables unattended oper-ation, for instance, solar cells onboard satellites. It produces no waste or

gases: it is clean.

Although the cost of solarpower generation is at presentsuch that it precludes thewidespread adoption of solarpower generating systems, it isexpected that prices will falldramatically over the next 10-15years.

Solar collectorsSolar collectors are normallyconstructed in a way that allowsthe incident sunlight to be col-

lected and converted into heat.The main types of collector areflat, concave, and heliostat. Theflat type has the advantage ofbeing able to operate from dif-fused light: the other two canonly work from direct sunlight.All solar collectors operate onthe same basic principle:sunlight falls onto a blackenedabsorbent surface and heats thematerial immediately under-neath that surface. The materialis often water, but it can also beair-see Fig. 1. To protect thecollectors from atmospheric ef-fects and soiling, they are com-monly covered by a sheet ofPerspex.Concave (parabolic) solar col-lectors are able to generatetemperatures of up to 4,000 C.

They are usually constructed asa dish similar to satellite TVantennas.Heliostat -type solar collectorsmake use of plane or concave

la

3

45

b

1 incident light2 double Perspex cover3 selective metal structure4 cold air input5 hot air exit

1 incident light2 Perspex cover3 second Perspex cover4 blackened surface5 copper water pipes6 insulation

87107 -la

Fig. 1. Typical solar collectors operating with (a) water, and (b)air.

minors that can be rotated(nowadays usually under com-puter control) to follow the sunacross the sky-see Fig. 2. Thistype of collector affords effi-ciencies of up to 30%.Solar collectors generally have

ItEEJuly August 1987

good efficiencies and are get-ting cheaper. This is particu-larly so in the case of flat types,which are used more and morein the roofs of industrialbuildings as well as in those ofprivate houses-see Fig. 3.

1111111111117

4-main water supply

57107-3

Fig. 3. Flat solar collectors installed in the roof of a privatehouse.

Fig. 2. The immense solar furnace at Odeillo in the French Pyrenees Mountains. The furnace uses a large number of heliostats, whichdeflect the sunlight onto a concave mirror. The total surface area of the heliostats is 2000 m2; the mirror is 39 m high and 54 m wideand its focal length is 18.4 m.

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July/August 1987

MHD generatorsMagneto -hydro -dynamic gener-ators convert thermal energydirect into electricity. A sche-matic representation of such agenerator is shown in Fig. 4.The thermal energy is obtainedby heating a gas to some2500 °C by means of a largeconcave solar collector. Whenthe temperature of the gasreaches 2500 °C, ionization oc-curs. This causes the gas mol-ecules to accelerate to speedsof well over 300 m/s. The gas isthen passed through a mag-netic field, which separateselectrons and ions, whereby anelectric current is generated.This type of generator is still inits infancy, although large pro-totypes are already in operationin the USA and the USSR. Themain problem is the heating ofthe gas to the high temperaturerequired. None the less, theprototypes work well and showefficiencies of up to 55%.

24

Solar cellsSolar cells provide an attractiveand promising source ofalternative energy. Unlike solarcollectors, they provide ameans of direct conversion ofsolar energy into electricity.

Types of solar cellCrystalline silicon, Si. By farthe largest proportion of solarcells currently manufacturedare made from crystalline sili-con. The basic construction ofthis type of cell is shown inFig. 6. Its operation will be dis-cussed later in this article.

Amorphous silicon, a -Si.Amorphous silicon is, accord-ing to many researchers, thesolar cell material of the future,because its production costsare a fraction of the price ofcrystalline silicon.

Amorphous silicon can beformed by a number ofmethods, such as sputtering,pyrolysis, and high -frequencyglow discharge. At present, theglow discharge method ispreferred. In this, a substrate isheld at a temperature of about300 °C in a vessel in which thepressure is about 5 ton. Siliconhydrides, such as Silt! or Si211,5,or silicon tetrafluoride, SiF.; are

4 1 concave mirror2 healing chamber3 gas jet4 electrodes5 heal exchanger6 condenser (cooled)7 condenser pump

(the magnetic field is atright angles to the papersurface)

3 4

7

5

Fig. 4. Schematic representation of the magneto -hydro -dynamicgenerator used in the UO2 plant in the USSR.

Fig. 5. Solar tower installation at Albuquerque in the USA. Thistype of installation is economically viable only where very largepowers are required. It consists of a tower some 300 m high,around which plane or parabolic heliostats are grouped in circles.The mirrors beam the sunlight to the top of the tower where thesolar collector is situated. The solar energy is converted into heatwhich is used to drive a large turbine.

-I

87107-6

antirelleclion coatinggrid electrode

n -region

p n junction

p -region

hack surface electrode

Fig. 6. Basic construction of silicon solar cell.

Table 1 Performance of various solar cells

Type of solar cell Conversionefficiency

(%) Costs

Siliconmonocrystalline 12 fairly highpolycrystalline 15 highamorphous 8-10 very low

Copper(lisulphide-Cadmiumsulphide 7-9 high

Gallium -Arsenide 21 very highCadmium -Selenium 6-7 not known

introduced into the vessel.When an HF voltage is applied,amorphous silicon begins to ac-cumulate on the substrate. Dop-ing of the a -Si is achieved byadding a phosphorus hydride,such as PH3, for n -type, or aboron hydride, such as B2H6, forp -type.

Copper(I)sulphide-Cadmiumsulphide, Cu2SCdS. The elec-trical characteristics of this typeof semiconductor are promis-ing, although research into thematerial is still going on. Fromearly prototypes, it is clear thatboth high efficiencies and highpower outputs can be obtained.

Gallium -Arsenide, GaAs.Although this type of materialaffords a very high effciency, itis expensive to produce. How-ever, it has a non-linear light -power characteristic, whichmakes it particularly interestingfor use in combination withconcave solar collectors.Moreover, compared withcrystalline silicon, GaAs doesnot dissipate so much heat and,therefore, requires less cooling(smaller heat sinks).

Cadmium -Selenium, CdSe.This type of solar cell is still inthe development stage.

Table 1 gives a comparison ofthese various types of solar cell.A number of other materials areactively being investigated inlaboratories all over the world,but at present it does not looklikely that these will find com-mercial application in thiscentury.

Basic operation of asilicon solar cellThe characteristic behaviour ofa semiconductor depends onthe nature of the constituentatoms and on the way in whichthese atoms are groupedtogether. In other words, it is afunction of the atomic structureas well as of the crystal struc-ture of the semiconductor.An atom consists of a positivelycharged nucleus surroundedby negatively charged elec-trons located in discrete orbits(shells) around the nucleus.Electrons can exist in stable or-bits near the nucleus only forcertain discrete values ofenergy, called energy levels ofthe atom. The allowed energies

Conduction band (empty)

Forbidden gap

Fig. 7. Energy level diagram (simplified) of a semiconductor.

of electrons in an atom arerepresented by horizontal linesin the energy -level diagramshown in Fig. 7. Not more thantwo electrons can occupy alevel: this results in electronsfilling up the lowest possiblelevels first.Since the atoms in a semicon-ductor are closely packedtogether, there are very manyenergy levels associated witheach nucleus (because of theinteraction between the atoms).This results in the energy -leveldiagram for the material be-coming an energy -band dia-gram (each band contains verymany levels).The lowest energy band iscalled the valence band: this isfilled with electrons, sincethere is an electron for each ofthe energy levels contained inthe band. The upper energyband is virtually devoid of anyelectrons: it is called the con-duction band. There is a smallforbidden gap between thevalence and conduction bands.Because of the thermal energyof the semiconductor at roomtemperature, some electronscan cross the forbidden gapinto the conduction band. Theconsequent empty energy levelin the valence band is called ahole.The total current resulting fromthe electrons in a filled valenceband is

j = nev = = 0 [1]

where j is the current density, n

the electron density, e the elec-tron charge, and v the averagevelocity of electrons in thevalence band.lithe kth electron crosses to theconduction band,

e in =l. i.kt'l = [2]

from which it is seen that thevacancy (hole) in the valenceband can be considered as apositively charged carrier fullyanalogous to the negativelycharged kth electron. The vel-ocity of the hole is equivalent tothat of an electron in the sameenergy level.At absolute zero, all the elec-trons occupy the lower energylevels, the valence band is filledto maximum energy, and nohigher levels are occupied.This level of maximum energyis called the Fermi level, EF,which is approximately con-stant with temperature. Whenthe temperature is at roomlevel, the electrons in a semi-conductor are distributed be-tween the valence band and theconduction band, and the Fer-mi level lies in the forbiddengap.Since the Fermi level is constantthroughout the silicon, theenergy bands at the junctions inFig. 8 are distorted, whichcauses an electric field accrossthe junction. This field is calledthe built-in field.When the silicon p -n

junction-see Fig. 8a-is inequilibrium (no bias), the cur -

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July August 1987

Fig. 8. Energy -band diagrams of a silicon p -n junction under dif-ferent bias conditions. The net current across the junctiondepends on the strength of the built-in field, which is increased(b) under reverse bias, and reduced (c) under forward bias. Thedepletion layer is directly proportional to the built-in field. Thebuilt-in field, E=Uo/x. where Uo is the potential rise at the p -njunction due to small electron -hole pair movements in the semi-conductor, and x is the width of the p -n junction.

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July/August 1987

rent /1 resulting from electronsdiffusing from the n -side isequal to the current Iz whicharises from electrons leavingthe p -side. If a positive voltageis applied to the junction-seeFig. 8b-the built-in field is in-creased. The number of elec-trons diffusing from the n -region is then much smaller,since only few electrons havethe energy required to over-come the built-in field. How-ever, the number moving fromthe p -region to the n -region isnot affected, because theseelectrons encounter no field.Therefore, a net current flows,but it is limited by the smallnumber of electrons in the p-region. If the polarity of the ap-plied voltage is reversed-seeFig. 8c-the built-in field is re-duced and /1 is large becausethe number of electrons in then -region is so large. As before,Iz from the p -region to the n -

region remains unaffected. Thenet current is then large andcorresponds to the forwarddirection.The net current, I, underforward -bias conditions is givenby the exponential expression

26

1=10 [exp(eVInk7)-1]

where /0 is the reverse satur-ation current, e is the electroncharge, V the applied voltage, na factor between 1 and 2representing the deviation fromideal diode characteristics, kthe Boltzman constant, and Tthe absolute temperature.In a silicon solar cell, in theabsence of incident light(called the dark state). the ex-pression for the dark current, /ais identical to that for I in for-mula [3].When the cell is illuminated, aphoto -generated current, /ph,flows as junction reverse cur-rent. This current is directlyproportional to the intensity ofillumination. From Fig. 11 it willbe seen that the net current, I, isgiven by I = -Iph+ /a =

-lph +1.[exp(eVInitT)-1] [4]

The voltage /A, across the loadand the current h through itproduce an output power Pp,which is equal to Mk or /0/?1,,and is the direct result of the in-cident light falling onto the cell.Finally, Fig. 12 shows that thesensitivity of a silicon solar cellis greatest at a wavelength ofabout 0.8 pm, i.e., at the lower

Fig. 9. Photovoltaic effect in unbiased p-n junction.

Fig. 10. Current -voltage characteristic of silicon solar cell.

Fig. 11. Basic circuit of illuminated solar cell connected to load.

Fig. 12. Spectral response of a typical silicon solar cell.

end of the band of visible lighttowards the infra -red region.

References:

Physics of atoms and moleculesby B. H. Bransden and C. J.Joachain

Quantum physics of atoms,molecules, solids, nuclei, andparticlesby Robert Eisberg and RobertResnick

Die Technik der Solarzelleby Diaz Santanilla

EE

July August 1987

LASERS: AN OVERVIEW

The development of lasers since they first appeared in the early1960s has been spectacular. In just over 25 years they have

become virtually indispensable in such diverse applications ascompact disc players, fibre optic communications, surgery, and

the Strategic Defence Initiative.

The first lasers appeared in1960-61 when Javan, Bennett,and Herriott of Bell TelephoneLaboratories announced thehelium -neon laser just afterTheodore Maiman, working atthe Hughes Aircraft Corpor-ation, had made a practical rubylaser. In little over a year later asemiconductor laser had beendeveloped more or less simul-taneously in Britain and theUSA.

FoundationsAn atom may be represented bya Bohr model: Fig. 1 shows thatof a hydrogen atom. Bohr con-sidered one electron of charge-e and mass m, moving withspeed v, and acceleration stairin an orbit around a centralnucleus of charge +e. Inclassical physics, chargesundergoing acceleration emitradiation and would, therefore,lose energy. On this basis, theelectron would spiral towardsthe nucleus and the atom wouldcollapse. Bohr thereforesuggested that in those orbitswhere the angular momentumis a multiple, n, of h/217, theenergy is constant. In the early1920s, de Broglie proposed thatan electron may be consideredto behave as a wave of wave-length ).=h/p, where It is thePlanck constant (4.14 x 10-15 eV s)and p is the momentum of themoving electron.If the electron can behave as awave, it must be possible to fit a

Fig. 1. Bohr's model of thehydrogen atom.

whole number of wavelengthsaround the orbit. In that case, astanding wave pattern is set upand the energy in the wave isconfined to the atom. If thereare n waves in the orbit and A isthe wavelength,

IA =2w-

- so that,

).=2rir/n =h1p=h/mv

from which,

mvr=nh/2n

This shows that mvr, the angularmomentum of the electron is annth multiple of h/2n.In Fig. 1, the electron movingaround the nucleus has kineticenergy due to its motion andpotential energy in the elec-trostatic field of the nuclearcharge +e.Bohr calculated the total energyE of the electron in terms of itscharge, mass orbital radius, andthe number n which quantizesthe angular momentum. Hethen assumed that the electroncan pass from one energy levelto another. If, for instance, theelectron jumps from energylevel E3, corresponding ton =n3, to a lower level £2, corre-sponding to n=n2, the differ-ence in energy is released asradiation of energy hv, where his the Planck constant and isthe frequency of the radiation.Therefore,

E3-E2=hv=hc/).

where ,t is the wavelength of theradiation and c is the speed oflight in a vacuum.Although Bohr's theory of thehydrogen atom was unable topredict the energy levels inatoms with many electrons, itsfundamental ideas remain valid.For instance, the angular mo-mentum of the electron hasquantum values, and the energylevels of an atom have onlydiscrete values: Eo, Et.

Fig. 2. Model of a many -electron atom. When an electron jumpsto a lower energy level, a photon is released.

£2...E=.; no other or in-termediate energy level is poss-ible. The lowest energy level,Eo, is called the ground stateenergy. All physical systems arein stable equilibrium in thelowest energy state.If an atom absorbs energy, andthe energy of the atom reachesone of its discrete levels, El, theatom is said to be in an excitedstate. Once an atom has beenexcited to a higher energylevel, En, it will try to reduce itsenergy. The energy lost if theatom reverts direct to theground state is Er-Ea. Thisenergy is radiated in the form ofelectromagnetic radiation, i.e.,quanta of energy itv-see Fig. 2.These quanta are calledphotons. The frequency of thephotons lies in the range 5 nmto 10 urn. From the foregoing, itfollows that

hv =En-Eo.

An atom can interact with aphoton in three ways: absorp-tion, spontaneous emission,and stimulated emission-seeFig. 3. If an atom absorbs aphoton of energy and thedifference in energy levels ofthe atom is equal to hy, the

3

F0

E

E

absorption

si:cntv.sciserrniss:on

passon

E 1 excited state

£0

emon

Fig. 3. An atom can interactwith a photon in three ways.

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July/August 1987

photon will raise the atom to ahigher energy level. In spon-taneous emission, an atom inlevel 3 may of its own accordemit a photon by, leaving theatom in the lower level 2. Instimulated emission, an atom inlevel 2 may be stimulated toemit a photon hi, by interactionwith another photon of the sameenergy.If in a system of atoms with anenergy level Er above theground state there are nophotons of energy Er-Eo,.where Es is the ground stateenergy, the atoms remainstable. If, however, a fewphotons of energy En-Es areintroduced, these will immedi-ately stimulate the emission of anumber of photons of the samekind. This increases thenumber of photons in thesystem, which in turn stimulatethe emission of more photons.In this way, an avalanche effectis produced, which results in allatoms in the system rapidly giv-ing up their photons-seeFig. 4. This process is calledlaser action (light amplificationby stimulated emission ofradiation).In a system of atoms in thermalequilibrium, the number ofatoms in the ground state ismuch greater than that in ahigher energy state. This iscalled a normal population ofatoms. In such a system at tem-perature T, the numbers, ni and112, of atoms in two successivestates, El and E2, are related bythe Boltzmann formula (inwhich k is the Boltzmann con-stant - 1.38 x 10-23 J K-1):

112 =n1 exp[ - (E2 - E1)/k7)

28

from which it is seen that atroom temperature (T=300 K), n2is considerably smaller than nl,i.e., a normal population ob-tains. If it is possible to maken2>r11, a population inversionis produced, which enableslaser action to take place.The output from a laser may becontinuous (CW operation) as isusually the case with gas lasers,or pulsed as that from solid-state lasers. Table 1 lists a var-iety of lasers and some of theircharacteristics.

Three -level lasersAt present, the main solid-statelasers are the ruby (Cr' -) andthe neodymium/yttrium alu-minium garnet (Nd/YAG) lasers.The ruby laser is a three -level

0

se

0 00

00

00 ®Q-

0

0

atom Photon

laser beam

SE = sinectardt=1 en: r.

Fig. 4. Illustrating the avalanche effect if a photon or photons areintroduced into a system of atoms.

Type oflaser

Pressure Efficiency Power Wavelength

He-Ne 0.1-25 mbar 0.01-0.5% 0.1-10 W 632.8 nm1.15 um3.39 urn

CO2 1.3 bar 10-30% 10-100 kW 9.6-10.6 um

X E2 30 bar 30% 200 nm

Dye 10-15% 0.1-10 W

Cr3- 1% 1000 W+ 694.3 nm

Nd/YAG 1% 1-500 W 1.06 urn

GaAs 0.1-0.5 W(pulse:1 kW-)

900 nm

Various lasers and some of their characteristics.

Fig. 5. Artist's impression of the construction of a ruby laser.

Fig. 6. Operation (simplified) of a three -level laser.

laser (E2>E1>Es), with a fastdecay between levels 2 and 1,and a slow decay between Iand 0. A typical construction ofthis type of laser is shown inFig. 5.Ruby consists of a small con-centration of Cr3- ions in a lat-tice of crystalline A1201 When ahigh potential is applied to theflash tube, the ions are excited,or pumped, by photons ofwavelength 550 nm (green light)and energy E2-Eo-see Fig. 6.The excited ions decay spon-taneously to the lower energystate E1, emitting photons ofenergy E2-E1.The energy state Ei has thespecial property of having alarge stimulated emission prob-ability and a low spontaneousemission probability. It is,therefore, filled with a fargreater number of ions than theground state Es. There is thus apopulation inversion betweenthese two levels, so that laseraction can be initiated, resultingin the emission of red light(1.=694.3 nm).

Four -level lasersExcept in a few cases, such asin the ruby laser, it is difficult toproduce a population inversionbetween a ground state and anexcited state, because initiallyall the atoms are likely to be inthe ground state, and more thanhalf the atoms have to bepumped to level 2 before apopulation inversion can beachieved. An easier method ispossible in a four -level laser inwhich a population inversion iscreated between two excitedlevels-see Fig. 7. Initially, allthe atoms are in the groundstate, Es, and none in the ex-cited states 1, 2, and 3

(E1<E2<E3). Level 3 is chosenso that it has a fast decay to level2, and pumping between levels0 and 3 immediately produces apopulation inversion betweenlevels 2 and 1. As level 2 beginsto fill up by the stimulated emis-sion at frequency (E2-E1)1.17,the population inversion willdecrease. To minimize this ef-fect, level 1 is chosen so that ithas a fast decay to the groundstate.Gas lasers are examples of amulti -level system, which canbe pumped by an electrical dis-charge rather than by incidentradiation. An important modelis the He-Ne laser, in which the

7

£

Ei

Eo

\est decay

upper laser level

stimulated emission

/fast decay

lower laser *ref

grcsmd state

Fig. 7. Operation (simplified) of a four -level laser.

active material is a mixture ofhelium and neon gases con-tained at low pressure inside along quartz tube with opticallyplane mirrors at each end-seeFig. 8. Two terminals near theends of the tube enable a highpotential to be applied to pro-duce a discharge in the gasmixture. A typical constructionof a He-Ne laser tube is shownin Fig. 9.In an electrical discharge, thehelium atoms are raised to the2'S and 23S levels which aremetastable-see Fig. 10. By col-lision with these atoms, the

neon atoms are excited to level3, so that a population inversionis produced and laser actionoccurs as explained above. Thewavelength of the emitted lightdepends on the reflectivity ofthe mirrors between which thegas is placed. Oscillation willtake place at the wavelength forwhich this reflectivity is a maxi-mum. In Fig. 10 it is-typically-633 nm (red light). It is seen thattwo other beams are also gener-ated: one at 3.39 pm and one at1.15 pm, but these are effec-tively suppressed by filter ac-tion of the mirrors.

Polarization of laserlightAlthough laser light is coher-ent, because all the photons (orwaves) are in phase, polariz-ation is random-see Fig. 11. Tolinearize the polarization, aBrewster window as shown inFig. 9 is used. Such a window isa disk of plane glass (see Fig. 8)which is set at the Brewsterangle to the incident light to en-sure that only light of a givenwavelength is passed.Brewster's law states that whenlight strikes a glass surface at anangle of incidence given bytan -'(n), where n is the refrac-tive index, the reflected light isplane polarized. At this angle ofincidence, the refracted raymakes an angle of 90° with thereflected ray.

Resonance cavityThe laser emitter is placed be-tween parallel mirrors so thatphotons can be reflected backand forth many times, resultingin the build-up of a large photondensity by the avalanche effect.

lases beam

Fully uamscarentmirror

Fig. 8. Artist's impression of the construction of a He-Ne laser.

Fig. 9. Cross-sectional view of a He-Ne laser (courtesy of Siemens).

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July/August 1987

It is, of course, necessary thatone of the mirrors be partlytransparent, so that some of thelight can get outside the tubeused.The mirrors may be plane orcurved as shown in Fig. 12.When plane mirrors are used,part of the emission may bereflected spuriously outside thesystem. Such losses must bekept small: reflections must behigher than 99%. When con -focal mirrors are used, thebeam is kept exactly parallelwithin the cavity. The slightdivergence at the exit is con-trolled by a collimating lens.

Beam spreadMany laser tubes are markedwith their internal beam radius,n31, from which the beamdiameter, D., at a distance mcan be calculated:

Dx=20m

where 20, the angle of spread,is equal to Ihrrth: A is the wave-length of the laser light.If, for instance, a He-Ne laser,operating at a wavelength of633 nm, has an internal beamradius of 0.375 mm, the beamdiameter at a distance of 100 mis

Dieo=29m=2rrz1habi

=2 x100 x633 x10-3/3.142 x 375 x10-6=107.5 mm.

Lasers andtheir applicationsSince the development of laserscontinues at a spectacularspeed, only an outline of thestate of the art will be given.He-Ne lasers, because of theirsmall output (0.1-10 mW) arebest suited to use in labora-tories and measurement tech-niques, but are also used formedical purposes. Their wave-lengths are 632.8 nm, 1.15 pm,and 3.39 pm.Argon -ion lasers, with outputsof up to 15 W, are frequentlyused in medicine for photocoagulation. Their bluish greenlight (488 nm and 514.5 nm) isselectively absorbed by hae-moglobin and melanin. Theirmain application, however, liesin the field of eye surgery.Carbon -dioxide (CO2) lasers,operating in the infra -red

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July/August 198730

10225-

21

20

18

17

16

2'S

23S

- selaxaton viacoresionswith wed

t ground state

Fig. 10. Schematic representation of the operation of a He-Nelaser. The capital letter S is a code associated with the value ofthe total electronic orbital angular momentum quantum numberL. The lower case letters s and p are used in the so-calledspectroscopic notation, in which the value of the orbital angularmomentum quantum number L is indicated. The superscripts tothe left of the S give the value of 2S--1, or multiplicity, which isequal to 1 for singlet (S=0) states, and 3 for triplet (S=1) energystates.

Fig. 11. Light may be randomly polarized, but in a number oflaser applications it is required to be linearly polarized.

13

weld

lases tea,.

capilarift

Fig. 13. Illustrating the operation

region (9.6-10.6 pm), are pri-marily used in industrial appli-cations: hardening; drilling;welding; refining; and ageingare but a few of these. The useof a CO2 laser for industrialwelding is illustrated in Fig. 13.The dye laser is pulse operatedand pumped by a xenon flashtube-see Fig. 14-or by apulsed beam from anotherlaser. Continuous tuning of this

Fig. 12. It is essential that standing waves are generated between the mirrors terminating the res-onant cavity. The shape of the mirrors has an effect on the efficiency of the laser.

of a CO2 laser in industrial

type of laser is possible by mak-ing the grating that forms oneend of the resonant cavity rotat-able. With its very narrow linewidth and large frequencyrange, the dye laser is emi-nently suitable for use in spec-troscopy and in the chemicalindustry.Solid-state lasers fmd almostuniversal application inmeasurement techniques, be itthe exact distance from theearth to the moon or the speedof motor vehicles. Many ofthese techniques are by-products of military research.The only solid-state laser to beused in the medical world is theNd/YAG laser. Because of itshigh power output (>100 Wcontinuous) and operation inthe infra -red region (0.9-1.35 i/m), this type of laser is par-ticularly suitable for operationsin soft tissues, such as theremoval of tumors in theoesophagus.Solid-state lasers can producepulses of extremely highpower a power of 100 TW(=10'4 W!) at the peak of a 2 nspulse has been reported. Suchenormous powers are neededin the strategic defence in-

Fig. 14. Artist's impression of a dye laser.

Fig. 15. Semiconductor (GaAs diode) laser.

itiative and in research intonuclear fusion. The exit beamdiameter of such lasers is ar-tificially increased to about 1 mto prevent vaporization of thelenses.By far the most common lasersnowadays are semiconductoror injection lasers. Theselasers are based on the fact thata population inversion of elec-trons can be achieved by apply-ing a voltage across the p -njunction of doped gallium -arsenide (GaAs) material. Semi-conductor lasers are availablefor operation from the nearultraviolet to well into the infra-red regions. An artist's impres-sion of the construction of aGaAs laser is shown in Fig. 15.Semiconductor lasers are ofprime importance in moderncommunications, opticalmemories, and in compact discplayers. In fibre optic communi-cations, for instance, theyenable transmission rates of1400 Mbit/s to be achieved.Without the small dimensionsof the diode laser, it would nothave been possible to developthe compact disc player. A veryrecent development based onthe diode laser is compact discvideo.In the fore -front of laser devel-opment is the excimer laserwhich uses diatomic rare -gashallides as the active material.This type of laser was de-scribed in .the February 1987issue of Elektor Electronics.

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July/August 1987

CommercialconsiderationsIn 1986, the world market forlasers amounted to more than£425 million. The largest sectorswere research and develop-ment, and materials processing-see Fig. 16. When studyingthis figure, it should be borne inmind that the diode laser for aCD player costs only about £3,whereas an industrial modelmay cost as much as £30,000. Itis expected that the lasermarket will have grown toaround £1,000 million by theearly 1990s.

References:Advanced level physics by

M. Nelkon and P. Parker

Optics and its uses byG. F. Lothian

Physics of atoms and moleculesby B. H. Bransden andC. J. Joachain

Quantum physics of atoms,molecules, solids, nuclei, andpanicles by Robert Eisbergand Robert Resnick

Physics by David Hallidayand Robert

Fundamental University Physicsby Marcelo Alonso andEdward J. Finn

Fig. 16. Division of the world market for lasers in 1986.

EE

July/August 1987

THE MAC SYSTEM

An introduction into the characteristics of the televisiontransmission format generally expected to become the follow-up

of the by now technically outdated PAL and SECAM systems.

The curious thing about thenew Multiplexed AnalogueComponents (MAC) TV formatis that everybody seems to bewaiting for everybody else tostart doing something about it.Workers in laboratories of mostbroadcasting authorities havelong since established thatMAC is superior in nearly everyrespect to PAL, SECAM, andcertainly NTSC; they laid downthe target technical character-istics, and conducted manyexperiments to verify the per-formance of MAC in satellitelinks and cable networks. Whythen is MAC not being used atpresent, when it is such apowerful standard? Answeringthis question is not easy, and re-quires considering some as-pects not directly related totechnical matters, our main con-cern here.To begin with, there is the evol-ution of the MAC standard tostudy-see Fig. 1. From this it isimmediately apparent that thereis no single MAC standard, buta series of versions derivedfrom the original A -MAC sys-tem, which, like I -PAL, nevergot out of the laboratory testphases. E (extended) -PAL, withthe IRA as the main protagonist,was rejected by the Govern-ment's Advisory Panel in favourof D2 -MAC four years ago. B -MAC was supported mainly byPlessey for use in TV studiosand microwave links, butproved impossible to imple-ment on TV satellites. C -MAChas three subsets, developedand supported by differentauthorities and satelliteoperators, who are, of course,keep on winning the generalacceptance of their particularsystem. That a single MACtransmission format will be withus soon is very unlikely, how-ever, considering that everysystem has its own merits for agiven application, as will beseen further on. Of the three C -MAC subsets, D -MAC, the ver-sion optimized for cable net-works using 10.5 MHz band-

width and AM VSB (vestigialsideband), can be disregardedin the coming discussion onwho is to rule the airwaves.Although both C -MAC and E-CMAC (enhanced C -MAC) areclaimed to be suitable for thefuture HDTV format and its BBC -supported derivate, DATV,

there are other, important, con-siderations to this matter, andthis will be reverted to in duecourse.

Waiting for MACCurrently, the majority of satel-lite TV programmes are trans-mitted in PAL, using analogueFM and low -power transpon-ders operating in the CSS band(10.9-11.7 GHz). The D2 -MAC TVstandard is only used for ex-perimental transmissions by theNOS on the ECS-1 transponder

formerly used by Europa -TV,while the Swedish national TVprogrammes are transmitted ina version of C -MAC via Nordic -1at OP 1°W.Semiconductor manufacturersintent on producing MAC de-coder chip sets are waiting forthe DB satellites to come intooperation, while transponderleaseholders are afraid tochoose a particular MAC formatsimply because...chips andready-made multistandard de-coders are not yet available. Sofar, it seems that only ITTSemiconductors have managedto state the target specificationof a D2 -MAC decoder. The diffi-culties in getting the French,German, Luxemburgian andpan-European DB satellites inorbit, and transmitting (E)C-MAC and/or D2 -MAC signalsfrom these, have the doubtfulbenefit of allowing more time

Fig. 1. Illustrating how the various TV transmission formats cameinto existence.

for semiconductor manufac-turers to spring into action andcome up with competitiveproducts, which are expectedto become widely availableonce the first MAC signal is be-ing beamed down. Until then,there is nothing but secrecy,preliminary specifications, andconfusion on the part of cablenetwork operators and individ-ual viewers.

The shortcomings ofPALIn a standard PAL signal, theluminance and chrominancecomponents are separated inthe frequency domain-seeFig. 2a. The presence of thechrominance subcarrier inthe transmitted spectrum givesrise to an overlap area withluminance components abovesome 2.5 MHz. The effect of thiscan be seen on any PAL com-patible colour TV set as spuri-ous cross -colour patterning onareas of fine detail in the pic-ture, and is caused by thereceiver's decoder circuits mis-taking fast luminance (black -white) transitions for chromi-nance information. Also, sound -on -vision patterning and visionbuzzing occur readily when thePAL TV receiver is not properlyaligned, or when the transmit-ter produces intermodulationowing to non-linear operationor improper filtering.Figure 2b is a simplified rep-resentation of the time structureof one of 625 lines in a PALcolour test signal. The durationof the line is 64 ps, but of thisonly 52 ws contains picture in-formation, namely 8 colourbars. The remaining time (12 µS)is the line blanking period,composed of the line syncpulse, front and rear porch, andthe 4.43 MHz colour burst. AMAC picture is still made up of625 lines, but the luminance (Y)and chrominance (U/V) compo-nents are separated in the time

EE

July/August 1987

domain, i.e., transmittedsequentially within the avail-able line time of 64 As. Fig-ure 2d shows that the analogueY and U/V components are ex-tracted from the composite in-put signal, time compressed,and multiplexed together with adata burst, whence the acronymMAC. The process of time -compressing may be carried

out digitally or with analoguemeans (CCDs mainly), but bothmethods inevitably result in anincrease in the bandwidth ofthe baseband signal. Consider,for instance, the Y component:in the PAL and D2 -MAC signal ithas a duration of 52 and 34 As re-spectively. The compressionrate is therefore 52:34---3:2, andresults in the frequency being

increased by a factor 0.5, sincea shorter period is available forthe same number of level tran-sitions. Similarly, the colour dif-ference signal, U/V, is com-pressed by a factor 3:1. Theresulting time multiplexingscheme is shown in Fig. 2c.Note that the sound & datablock is entirely digital, andtransmitted in 2-4 PSK, a

modulation mode that will notbe discussed here. Some linesin the D2 -MAC picture arereserved for particular appli-cations-see Fig. 3 and consultthe technical specification inTable 1. The frame organizationof an enhanced C -MAC (E-CMAC) picture is schematizedin Fig. 4. E-CMAC has beendeveloped specifically with

2a

PAL

chrcrninance soundsubcarries subcarrier

+2 +4 +6f [MHz]

b

One syncword

White Yellow Cyan Green Purple Red Blue Black

% 1

% %

\ %

%

%

1

Burst% 1 1t k

Sync %

a a a 1

a 1 a 'a

clampingperiod

a a

\ ti

a aa Y a\ \ % 1 1

a , a a

\ a,

PAL

begin ofnext One

C

tense (64 on = 1296 clock cycled

d - 11 ty

02 -MAC

1296 x 15,625= 20.25 MHz (system clock)

D2 -MACclock cycles

sound anddata

Ldilc11:nteluminance

Y209 e, 29 349 697 e7. UN --I.

(compressed)4

(compressed).

I

EC ,us

1-1)?-k,

',[15

i

01 00und r% 1 colour difference

li

% i

OA±.....--/( los

data ,

U = odd OnesV = even lines

-1Luminance

Yf I, i0.5

X

i g/ r

LI

Note cp = clock periodT = 4 cps for transition from end of data.

15 cps for clamping (0.5V.)10 cps for weighted transition to UN period.

/ Ak._.)bas) I, ,-----11....1"4

TI T2 73 T2 = 5 cps for weighted transition between UN period and Y period.T3 = 6 cps far weighted transition from Y period.

not to scale 1 cp for data transition 87126-2

Fig. 2. Showing how the D2 -MAC signal is given its basic time -division multiplex scheme.

3

- end of odd frame

Ira,houndar

start of eves frame even trace

- end of fourth field -tart of First f lett (even) firs. 'le,. end of first field (e-vt$)-- start of second field (odd)Colour dif f field blanking interval Po-- field blanking interval

Data Lars[r- Luminance

Y.E'rm f"in E'Vm

1/ I 1 10...4=1=CCI-#--ICOIC:=1-4-4-,-1-620 621 , 622 623 1 62a , 625 1 2 3 , 4 , 5 r 21 22 r 23 24 25 , 26 s 309, 310 311 r 312 313 , 314

er of even frame start of odd frame --sy. and of odd frame

sec rd field -ad of second field --+.1--field blanking inters31-.4

W1G.

w2 01 WI

I I I 1 I 4-1-110%-arK._-)11=1C-DIF79-Ii=11CD1-11111111-1C0e=1=1C011=8-111111111.=315 r 316 r 317 i 310 133a 335 I 336 337 336 621 1622 623 624 1625 1 2 r 617 , 612 a 019 a 620 s 621 a 672 623 624 , 625

I t_ black revelreferencecolour

differencesignalonly

L'Um - odd numbered lines (23. 25. .... 621)E'Vm - even numbered lines (24. 26. 622)

wi and U, are the line synchronization cords

(phase transitions 2 to 6 in the data burst)

X - frame synchronising sequence - true fora

I - frame synchronising sequence - inverted fora

reserved forreference signalsdata 5arst occupies

whole lire

(rarebesusdar-y

87126-3

Fig.3. A MAC picture analyzed. Note the special function of lines 624 and 625 (courtesy EBUI.

EE

July/August 1987

464 asTable 1.

D2-MACiPacket

D = version indication.2 = bit rate division factor with respect to C -MAC.MAC = Multiplexed Analogue Components.Packet = digital sound and data are transmitted as composite bursts.

Transmission multiplex characteristics:

Duobinary coded, AMIVSB and Instantaneous bit rate during dat

C -MAC. Recommended deviation (FM):

Lines per picture: Lines with data burst: Lines with video signal Lines with luminance signal: Lines with chrominance signal: Interlace ratio: Aspect ratio: Luminance compression ratio: Chrominance compression ratio: Sampling clock frequency: Instantaneous bit rate of data

burst (2-4 PSK): Samples per line:

Chrominance samples: Luminance samples: Bits per data burst: Line 624:

Line 625:

FM compatible.a burst halved with respect to

13.5 MHz: V; pre -emphasis tran-sition at 1.37 MHz; energydispersal f (d)= "1,f (V)Ai= +300 kHz6251 to 62524 to 310 and 336 to 622Y in each lineU in odd lines, V in even lines2:14:3 (5.33:3)3:23:1

20.25 MHz

10.125 Mbitis1296

349697

105 (6 bits HSW and 99 bits data)105 bits and analogue referencesignals

648 data bits- 6 for H sync- 32 for clock run-in- 64 for VSW- 546 for service identification

Aerials for terrestrial and satellite TV services.

525lines

. \ \

/,

Colour Difference

Colour Difference

I/

Extension

Luminance

Sparei: -r-

/

iColour Difference

Colour Difference

fExtension

Luminance

4 Clamp Period shaded areas used torvideo extensions

Spare

Fig. 4. A frame of E-CMAC, showing that the length of thesound/data burst is reduced to achieve a wide-screen picture,allowing extra luminance information toIBA).

HDTV -compatible DB servicesin mind, and is strongly pro-pagated by the IBA in co-operation with the EBU.

MAC: some essentialpointsA discussion of all the techni-cal characteristics of C -MAC, E-CMAC and D2 -MAC is beyondthe scope of this article, and in-terested readers are referred tothe publications for furtherreading. A few basic consider-ations as to the composition ofthe signal will help in under-standing the implications of artessentially digital transmissionformat. The discussions applyto both D2 -MAC and C -MAC.

Synchronization. Each databurst contains one of two 6 -bitline synchronization words(LSWs-see Fig. 3), which aredefined as follows: W1=001011,while W2=W1=110100. The dataprocessor in the MAC decoderkeeps track of the samples ineach line, and arranges for theappropriate circuitry in the TVset to be actuated when an LSWis recognized. The pattern ofthe LSWs at the frame bound-aries (odd/even) also providesthe interlace information. Thedata burst in line 625 contains aframe sync sequence which im-mediately follows the LSW andwhich is defined as four bytes55h followed by the 64 -bits FSW65AEF3153F41C246h. This istransmitted in its true formpreceding even -numberedframes, and in its invertedform preceding odd -numberedframes.

be carried (courtesy

Encryption. Whatever its ver-sion, MAC is inevitably tied upwith viewers' fears of intricateencryption methods. The factthat picture components U/Vand Y are separated in timerather than in frequency makesit possible to use two effectivescrambling methods. One isdefining so-called cut pointswhereby the U/V and Y compo-nents are cut into two segments,and transposed within the rel-evant period. To restore thesignal to its intelligible form. thecut points (i.e., relative samplenumbers) must be identified toreconstruct the time schemeshown in Fig. 2c. The cut pointswithin the periods Rc and RLare derived from a 16 -bit

pseudo -random sequence gen-erator, whose validation key isonly known in authorized re-ceiver systems. The methodillustrated in Fig. 5a is calleddouble cut component rotationfor now obvious reasons (notethat the cut points shown arebut examples). The secondscrambling method availablefor MAC entails making the PSKdata block unintelligible in thereceiver. Bits can be processedas shown in Fig. 5b: a pseudo-random binary sequence isadded modulo -2 to the digitalsound and data stream, so thatanother authorization key is re-quired for correct processingin the receiver. The data blockenables satellite operators toimplement not only pay -per -view systems, but also entitle-ment checking, multi -channelsound, selective Teletext, over -air addressing for automaticcontrolling of VCRs, andviewers' status registration.

Sound. Contrary to conven-tional sound transmissionsystems, the MAC formatemploys a fully digital, multiple -channel audio format. Asalready shown, no subcarriersare used: instead, the trans-mission is switched at RF from

an FM signal to a 20.25 Mbit/s(C -MAC) or 10.125 Mbit/s(D2 -MAC) 2-4 PSK modulatedsignal. The 99 data bits of lines1 to 623 are combined into 82

packets of 751 bits, and in-terleaved at 94 -bit intervals. Apacket is thus a combination ofsound and data, and consists ofa 23 -bit header, an 8 -bit packetcode to distinguish betweentwo types of sound and data,and 720 bits of sound or data. Acyclic (23,12) error correctingGolay code is implemented inthe header to ensure correctpacket recognition when re-ception is impaired. C -MAC

and D2 -MAC support 8 and 4high quality sound channels re-spectively (S/Na80 dB whenC/N.Z.18 dB), but more can becarried when these are corn-panded (multi -language com-mentaries).

_Compatibility. All versions ofMAC are totally incompatiblewith PAL and SECAM. Thismeans that forseeably MAC -decoders are in essence

5a eat punts 14

(earlp!eno.(-----* (651

1

K

V /

1 i

(UN) " (LN1 Lumunercelaluck2 X block' block2

r")1

/ t

-U- AY

T

at

Inverter

FC

Prc-cedin

BY =Aye Ey-I

Exclusive

Or

(i)

ay

.12.5

165

(26B1

i

V,

XLuminanceIdcmkt

rrtI

T

RL

tCoding I.

I

Filtering

Linearadorifion

..0

Level

shift -11-

2T = 96LEns ( T is hat) Ire bit interval)

05.0626MH

Dit) =IjeC2ih 5 -Pi +103

hit) = trans! er ofduebiriaty litter:

11g ti t(r). T cos 2 T vT

;Iv) =o

11 255

- Dk

571266

Fig. 5. Two methods of encoding a MAC signal: double -cut component rotation (a), and Booleanencryption of the data block (b).

6

32-4E o

42 cI-a

25 C

256

Code

Conuerter

D? 2270

7ClamPtrgi

AGE

4

crane Cc,-narator.

PLL Fitter

576E2 csa c

1212

14

Da -a

Sivcer.

Syncrcnisatton

DI -Businter:ace

OM RESEt

Ij15

uira

Store

21-22

°versaSter-e

LoOOInter-PolattngFliter

De-scraToler.Ce,nter-(ea,er

LineInter -palatineFtItOr

Contrast

Muittpiter

tail ierFor

Packet 2

Teat

GoingandPt CuteDecoder

CnronaInter-PaiatingF, lter

Petreat

CCrOarattir

21-24.27-30

4Coin,

nil tip [Ever

Cotc,

Saturationmitipiver

IPeon e

II U 11123 61 <7 62 16 17 113

ErrorCorrection.Expansion.ErrcConcea.nent

denary

Control

, 2-E

0 ES

E

_ EE- Z7

Fig. 6. Block diagram of the Type DMA2270 D2 -MAC decoder (courtesy ITT Semiconductors).

EE

July/August 1987

transcoding interfaces whichperform all the functions dis-cussed, and in addition processand stretch the compressedU/V and Y components to givethe correct length and contentfor a PAL/SECAM TV set. In-evitably, however, there wouldbe pressure on TV set manu-facturers to come up withmultistandard, that is, PAL -SECAM - D2 -MAC -C -MAC- E-CMAC compatible, sets

Abbreviations and terms usedin this article:

AM = amplitude modulation.BBC = British Broadcasting Cor-poration.

DBS = direct broadcasting sat-ellite.

DATV = digitally assisted tele-vision.

EBU = European BroadcastingUnion.

CCD = charge -coupled device.CD = compact disc.CSS = communication servicesatellite.

EIRP = effective isotropicradiated power.

FM = frequency modulation.f (V) = vertical sync frequency(50 Hz).

HDN = high -definition tele-vision.

IBA = Independent BroadcastingAuthority.

IARU = International Associationof Radio Unions.

IRT = Institut fur Rundfunk-technik.

NHK = Nippon Hoso Kyokai, thenational Japanese broadcastingauthority.

NOS = Nederlandse OmroepStichting, the national Dutchbroadcasting authority.

NTSC = National TelevisionSystem Committee.

OP = orbital position.PAL = phase alternation line.PSK = phase shift keying.QPSK = quadrature phase shiftkeying.

RTL = Radio TelevisionLuxembourg.

SECAM = Sequential Couleur AMemoire.

SES = Societe Europeenne desSatellites.

SIN = signal to noise ratio.VCR = video cassette recorder.VLSI = very large scale inte-gration.

= quadrature componentsof the chrominance signal:U=0.49(B-Y) and V =0.88(R -Y}.

VSB = vestigial side band.Y = luminance signal.df = deviation from the RF car-

rier in an FM transmitter.

EE

July/August 1987

equipped with high qualityaudio processors also. The firststeps towards proposing an all -digital TV receiver were thosefrom ITT Semiconductor. Thefunctional organization of theirType DMA2270 VLSI D2 -MACdecoder appears in Fig. 6. Apity the device is not yet gener-ally available!

Advantages over PAL. In con-clusion of this section, a sum-mary is given of the mainadvantages of MAC over PAL(and possibly SECAM andNTSC) systems: Excellent picture quality

thanks to separate trans-mission of luminance andchrominance components. Nocross -colour or cross -luminance effects.11 Ready driving of the de-

coder from the FM detector'sbaseband output. Less chrominance noise.I Significantly improved S/N

ratio at the same receiver in-put signal strength.III Capacity for carrying 4 or

8 CD quality audio channels.II Provision for additional digi-

tal services at 190 Kbit/s. Ready implementation of all -

digital, highly secure, en-cryption systems without in-creasing the baseband band-width.II Eminently suitable for incor-

poration in microprocessorbased timing and remote con-trol systems.

MACs, cables andsatellitesThe coexistence of C -MAC,D2 -MAC, and E-CMAC is aresult of research carried out invarious broadcaster's labora-tories. The comparison be-tween these formats focuses ona few main themes as discussedbelow:

Cable networks: C -MAC hasbeen optimized for satellitetransmission, where the chan-nel bandwidth is 27 MHz. Thisis generally not available inexisting cable networks, whichallow for a channel spacing ofabout 8 MHz. Reception of astandard C -MAC signal resultsin a compressed video band-width of about 8.5 MHz, in-terspersed with data bursts at20.25 Mbit/s. If re -modulatedinto VSB AM, the bandwidthis stilll around 15 MHz, due

7 Outer aperture

I

Inner reticle

1.33:caneenrional tetesisian

1.67:Eurapean 35-o.4-: wide-screen format... -I.75:European shooting format ( eidAttantic ratio)1 wide-screen

1.85:Vistavision'Panavisiaa formatr

2.20:70-iura film aspect rani*

235:Cinereascope

L J

Fig. 7. Commonly used picture aspect ratios normalized to unit area (courtesy EBU):

largely to the sound/data burst.When the sound/data packet isrecoded into duo -binary form,i.e., the data signal is at one ofthree levels, the 20.25 Mbit/sdata stream can be conveyedwithin a bandwidth of about8.5 MHz, which then equals thevision bandwidth. This enablesthe complete signal to fit withinthe available bandwidth oncable systems. The format somade is called D -MAC. D2 -MACis an even narrower signal thatcan be derived from D -MAC byhalving the bit rate in the databurst. This format results in abaseband bandwidth of around5.3 MHz, and can therefore betranscoded into VSB AM for useon cable networks where thechannel spacing is not less thanabout 7 MHz. It should be notedhere that transcoding alwaysresults in some degree of pic-ture impairment, and is, ofcourse, to be abandoned assoon as wideband cablesystems and MAC compatibleTV sets are available.

Satellites: Clearly the develop-ment of MAC formats was orig-inally prompted by the need forgood quality TV transmissionvia geostationary satellites. TheEBU recommends the use ofstandard C -MAC on their futureOlympus satellite, while the IBAproposes the E-CMAC format.The BBC is likely to agree uponusing D2 -MAC, just as theGerman and French DBS con-sortia. wri, on the SES-owned

Astra satellite are expected tokeep using PAL until MACdecoders are available every-where. Knowing that the BBCand IBA are likely to be as-signed quite a few channels onAstra, this one satellite may wellbeam down TV signals invarious formats once it isoperative. Its transponder band-width should be sufficient forconveying all 16 programmessimultaneously without runninginto cross -channel interference.

MAC formats, HDTVand DATVAlthough a separate discussionis undoubtedly required to de-scribe the technical charac-teristics of the many formatsalready proposed for HDTV, it is

worth while to study the com-patibility of this wide-screenformat with the MAC systemsdescribed. Successful demon-strations of high -quality largescreen pictures with an aspectratio of about 5.33:3 based on an1125 -line standard proposed byNHK of japan have given a newimpulse to researchers en-gaged in developing a newwide screen standard, as afollow-up of the 4:3 aspect ratiocurrently dictated mainly by thesize of colour picture tubes.Some of the most commonlyused picture aspect ratios areshown in Fig. 7. The system pro-posed by NHK is called MUSE,and its main technical charac-teristics are summarized inTable 2. The question nowarises which of the MAC trans-mission formats is most suitable

Table 2

Characteristics of the MUSE HDTV system

IN System: Motion -compensated multiple subsampling;multiplexing of colour signal by time -compression and integration.

Scanning: 1125 lines, 60 fieldsis, 2:1 interlace. Baseband bandwidth: 8.1 MHz (-6 dB) Re -sampling clock rate: 16.2 MHz Horizontal bandwidth: Y: 20-22 MHz for stationary picture

portions; 12 MHz for moving portions.C: 7.0 MHz for stationary picture portions:3.1 MHz for moving portions.

IN Synchronisation: positive digital sync. Audio and additional - PCM multiplexed in vertical blanking

information, interval using 4 -state DPSK at 2048 Kbitis

EE

July/August 1987

for conveying HDTV and higheraspect ratio pictures via satel-lite. Although all systems havebeen tested in this respect andfound to be compatible to someextent, the E-CMAC formatdeveloped by the IBA looksparticularly promising, since itis claimed to be able to providepictures of aspect ratio and res-olution comparable to those ofthe NHB proposals. This ismainly thanks to E-CMAC mak-ing very efficient use of theavailable time for the sound &data packet, at the expense of afew audio channels. The sam-pling rate is 27 MHz, while the

video bandwidth of an E-CMACsignal is about 12 MHz, bearingin mind that the picture is com-posed of 625 lines, and that theuncompressed sampling fre-quency is 22.5 MHz. Researchhas shown that E-CMAC 5:3 pic-tures can be transmitted usingconventional DBS channels inthe 12 GHz band. The reducedsound/data capacity with re-spect to C -MAC is still sufficientto convey 2 high quality soundchannels. A high degree ofcompatibility with standardMAC receivers is ensured byvirtue of the proportions of leftand right extension of the pic-

ture being signalled in line 625,the service identification line.The IBA claims that the qualityof an E-CMAC picture ap-proaches that of HDTV systemsusing around 1,000 lines, with-out the need to resort to a newand incompatible standard. En-hanced C -MAC pictures weredemonstrated at the Royal Tele-vision Society Convention inCambridge during September1985, and were shown to pressand industry representatives atthe IBA's Brompton Road head-quarters in December of thatyear.The transmission of true

The BBC's satellite test stationat Kingswood Warren.

8

Bit/s per Hz

10

2:-

9

o 8o 7

6

5

4

3

2

280

_a. 730

200

160

120

80

40

0

Mbit/s

t8 12 16 20 24 28 dB

S gnat -to -noise ratio

I

26,

- C)23

20

- 17

14

-------------1;

B

dB

dB

dB

dB

dB

8 12 16 20 24 28 MHz

Bandwidth with specified equivalent C/N ratio in 27MHz

400

320

280

240

200

120

80

4

Mbit/s

0 4 8 12 16 20 23 28 dB

Signol-tonoise ratio, measured in specified bandwidth

Mbit/s400

're, 360a.0

U 320

280

240

200

160

120

80

40

O 36MHz

27MHz

POPP-11MHz

1111111-1

12 14 16 18 20 22 24 26 28MHz

Equivalent S/N atio (as measured in 27MHz),for specified bandwidth

Fig. 8. Shannon's theoretical channel capacity as a function of four parameters. Note that 27 and 36 MHz are the most commonlyused bandwidths for satellite TV, and that C/N=11 dB is roughly the FM threshold (courtesy EBU).

EE

July/August 1987

1125 -line HDTV pictures by sat-ellite poses problems, however.The reason for this is that theunprocessed HDTV basebandsignal from the TV studio islikely to require a bandwidth ofabout 40 MHz, which equals abit -rate will over 600 Mbit/s iftransmitted digitally. The fol-lowing considerations willshow that this exceeds the ca-pacity of the currently used12 GHz band, because the re-quired data compression ratioof about 10:1 is as yet technicallyimpossible.Shannon has defined the maxi-mum bit rate (capacity), D,achievable in a communicationlink with bandwidth B as

D=Blog:(1+ C/N) bit/s

where C/N is the carrier tonoise ratio expressed in dB. Fig-ure 8 shows the capacity of thechannel in relation to variousparameters. Although some re-searchers have reached withina few dBs of the theoreticalShannon limit, this is only at lowbit -rates using substantial pro-cessing in the receiver. Withthe sort of bit -rate required forHDTV it will be difficult, if notimpossible, to approach half theShannon bound. Two examplesmay be considered to illustratethe foreseeable difficulty intransmitting an all -digital HDTVsignal:

B=30 MHz and C/No =94.3 dB:D=--- 195 Mbit/sB=19.18 MHz andC/No =94.3 dB: D=125 Mbit/s

C/No is the noise spectral den-sity expressed in dB/Hz, andcan be shown to equal a C/Nratio of 20 dB in 27 MHz. Assum-

ing that half the capacities Dcan be achieved, the limit is be-tween 60 and 100 Mbit/s de-pending on the maximum fore-seen degree of interference.QPSK signals have been shownto enable transmissions at about34 Mbit/s, while a relativelysimple extension to 8-PSKshould allow 51 Mbit/s to beachieved. This may be ad-equate for HDTV if 3:1 band-width reduction is applied inanalogue systems, and 10:1 bit -rate reduction (compression) inall -digital systems. In any case,the resulting bandwidth is stillfar beyond the capacity of theexisting DBS band, where chan-nels are allocated with a regular19.18 MHz spacing, and wherethe RF bandwidth of transpon-ders should not exceed about35 MHz to ensure acceptablelevels of interference. Con-clusion: 1125 line, all -digitalHDTV is currently impossible toimplement in the 12 GHz DBSband, and already experimentshave been conducted to assessthe propagation and attenuationcharacteristics of higher bandsallocated to DB services, i.e., 23,42 and 85 GHz. The results ob-tained by HDTV researchers TLong and L Stenger are valid forthe average European tempera-ture climate, and appear inTable 3. Note that the statedbands are not available in allIARU regions in the world.Based on these data, calcu-lations have been made asregards downlink budgets andsatellite EIRP figures. Depend-ing on the assumptions madefor the bandwidth, receiveraerial diameter, and minimumfigure of merit, the radiatedpower is foreseeably of theorder of 750 to 1,500 W per

Table 3

Attenuation and cross -polarization for different frequency bands.

Frequency MHO 12 a.. 42++ 85+

Percentage of worstmonth (1%) 99 99.9 99 99.9 99 99.9 99 99.9

Attenuation (dB) 1.5 4.5 4.5 13.5 11.6 35 19 57

Cross -polarization

(dB) 30 20 25 15 24 13 -Sky temperature (K) 85 200 270 -

Ms valum Ee.en are ',at prat:Ise; CIGSS.P0,..3fira tic," data for ,,..-61-4z ars not 4lraiq-31A. . CrcL-Spefarization doe to foe crystals -z sti:3 a largely oni,ns-e.n phanwrtenon ar,1 Care

needs to be taken %%ben corsktenng Qt., re -use of these fredualtc',es b-,,, n -.eons cfordtcgonat -.:t'arrzat,-,-.-,n.

channel in the 23 GHz band,and between 12 and 25 kW forthe 42 GHz channels. Evidently,regulating action is requiredfrom broadcasting authorities totimely avoid allocating too nar-row channels for the 40 to50 MHz wide HDTV services.Unfortunately, the internationalfrequency planning timetableis such as to make HDTV on23 GHz impossible before thebeginning of the next century.The BBC has recently proposedthe concept of DATV, whosemain advantage is found in thevery effective bandwidth re-duction of HDTV signalsoriginating from TV studios.Using DATV it becomes poss-ible to operate bandwidth re-duction procedures at thestudio level, and arrange for thereceiver to be instructed con-tinuously, via the data channel,on the organization of particularparts in the picture. The import-ance of DATV is that it enables asignificant improvement to beachieved in the quality HDTVpictures that can be conveyedin relatively narrow DBS chan-nels, thus efficiently using theavailable spectrum space.DATV is fully MAC compatible,and can be used to give anaspect ratio of 16:9 with slightlyhigher horizontal resolutionthan C -MAC. Like the MUSEsystem, it can make use of so-called motion vectors to effecthigh spatial resolution in pic-ture areas of predictable mo-tion.

ConclusionsAlthough the first MAC signalswill almost certainly be trans-mitted within a year or so, thereis no certainty as yet on thepreferred format for the variousservices. In this context, it ishoped that semiconductormanufacturers will providemultistandard MAC decoderchips based on design infor-mation from the research andengineering departments of thevarious broadcasting auth-orities mentioned. As to thefuture of HDTV, the main con-cern of researchers in this fieldwill be further studies intobaseband compression, strongbit -rate reduction, and ways ofimproving and enlarging exist-ing frame store devices. TheIRT in co-operation with theEBU has planned field trials

with HDTV for this and nextyear using experimentally op-erated transponders in theOlympus and Bopernikus sat-ellites. Bu

For further reading:

1) Specification of the systemsof the MAC/Packet family.Document Tech. 3258, availablefrom the EBU Technical Centre Avenue Albert Lancaster 32 B-1180 Brussels Belgium.The price is BF 2,000 includingpostage.

2) IBA Technical Review no. 21:Compatible Higher DefinitionTelevision. Available from theIndependent BroadcastingAuthority Engineering Infor-mation Service IBA CrawleyCourt I Winchester Hamp-shire 5021 2QA.

3)EBU Review (technical) no.219 (special issue on HDTV). Foravailability see 1).

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July/August 1987

THE COMPACT DISCIn the mid -1970s, engineers at the Dutch electronics companyPhilips felt they had developed just what the world had beenwaiting for. They called it the Laser -Vision videodisc. This is an

optically scanned disc which gives an hour of colour video andsound. Unfortunately for Philips, the video disc arrived too late:

too many people already had a video cassette recorder.Undismayed, the engineers continued their development, and in

early 1979 Philips unveiled a trimmed down version of thevideodisc, much smaller and containing sound only. It was

called the compact disc.

Because of the very favourablereception of the compact discsystem, Philips felt it had a newworld standard to replace theconventional (and vulnerable)gramophone record. Wisely, itcame to a joint agreement withSony to perfect the system.The first compact disc playerwent on sale in Japan in late1982, and in Britain six monthslater. At that time, a player costaround £500 and the discsabout £10. Now, just over fourand a half years later, areasonably good player can bebought for under £200, and it isexpected that prices will beunder £100 by Christmas. Thediscs have, however, risenslightly in price to about £12-14.

Production techniqueThe master (or blank) is made ofa glass disc that is ground andpolished to optical flatness-see Fig. 1. This is coated with alayer of photoresist, the thick-ness of which is controlled veryaccurately. The coating is oven -cured, after which the disc isready for cutting. Strictly speak-ing, the term "cutting" is incor-rect, because the recording iscreated photographically, butbecause of some parallels withthe production of a vinyl gramo-phone record, it has been re-tained.Cutting is carried out by a con-tinuously operating helium -neon (HeNe) laser, which isintensity -modulated by theaudio signal via an acousticmodulator. In the absence of anaudio signal, light can passthrough the modulator, but withan audio input light is scattered.The laser travels from thecentre of the disc to the outer asthe master revolves. The rota - 1

pownwii. p.

(e)Laser

cutting

(f)Develop

andetch pits

(g)Silver coat

by evaporation

Fig. 1. Some of the stages in the production of a compact disc.

2 Metal Polymer Substrate Bubble is one _.mor !err in diameter

Fig. 2. A bubble arises where the laser beam hits the surface ofthe coated glass disc.

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July/August 198740

Fig. 3. The surface of themaster after the developingand etching process.

tional speed of the disc is re-duced gradually in a way toensure that the speed of thelaser beam over the surface ofthe blank remains constant.The photoresist is then devel-oped during which the unex-posed areas are hardened.Subsequent etching removesthe exposed areas, which hasthe effect of creating pits in thesurface of the resist as shown inFig. 3. These pits represent thedigital information of the audioinput.The disc is then given a thinsilver coating to make it elec-trically conductive. At thisstage, it would be possible toproduce a commercial com-pact disc from the master. How-ever, to preserve the master,only a few (negative) copies,called "father" are made. Fromthese, a number of (positive)intermediate copies, called"mother" are made, and thesein turn produce a number of"sons" (negative). The sons arethe dies used to stamp compactdiscs. Since there are an evennumber of processes, the com-pact disc is identical to themaster.The compact disc is made of1.2 mm thick polymethylmetha-crylite, better known asPerspex, or of Makrolon, apolycarbonate plastic. The sur-face of the side of the CD thatcontains the audio informationis then given a thin layer of alu-minium, followed by a protec-tive coating of laquer. Thethickness of the aluminiumlayer is of the order of only10 rim, while that of the laquer isabout 5-10 pm. This side of thedisc is called the label side,because the identifying label is

Fig. 4. Typical construction of a laser pick-up unit.

printed or affixed here.The information is read from thedisc by a laser at the underside,i.e., through the Perspex orMakrolon. The laser, therefore,sees the pits as bumps. Atypical construction of a laserpick-up unit is shown in Fig. 4.

Structure of thecompact discFigure 5 gives a cross-sectionalview of a compact disc. Thelead-in track contains all thenecessary information regard-ing the recorded music orspeech. A total of some 20,000tracks are contained within the33 mm wide recording surface.The digital data are defined bythe length of the pits and thedistance between them. Thelength of the pits varies from833 nm to 3.56 prn, their width is500 nm, and their depth is110 nm. The distance betweentwo adjacent tracks is 1.6 pm.The disc contains some 7 x109bits. At a constant linear vel-ocity-CLV-of 1.2 ms-', themaximum playback time is74 minutes.The Perspex from which thedisc base is made has a refrac-tive index, n, of 1.46. Thediameter of the laser beamwhen it enters the Perspex is0.8 mm, but because of refrac-tion this is reduced to 1.7 pm atthe recording surface-see

diameter 120 mm

117mm

plastic protectionlayer

E

116mm

50 mm

46 mm

program area 33 mm

laser beamclamping area

t5 mm

coating layer

lead in \.e-26

mm-s.signalrecordingsurface

87137-5

transparent disc base

Fig. 5. Structure of a compact disc.

6

30*

laser focus

diameter oflaser beam=0.8 mm

Laser

recording surface

30*

by Snell' s Law:stn 30°/sin 20° =0.5010.34 = 1.46

ktransparentdisc base

Fig. 6. How the laser beam is focused onto the recordingsurface.

Fig. 6. This small diameter isone of the reasons that, say, adust particle of 0.5 mm does notaffect the reproduction of thedisc.

Pits and bitsThe pits and the reflective (alu-minium) surface representlogic Os and Is respectively.When the laser beam is fo-cused on a pit, ideally no lightshould be reflected. To achievethat, the depth of the pit, a, isapproximately equal to 114n,where A is the wavelength of thelaser light and n is the refractiveindex of the disc base.Since the diameter of the laserbeam at the recording surfaceis 1.7 µm, and the width of a pitis 0.5 pm, some light is reflectedfrom the pit. Because of therelationship between the depthof the pjt and the wavelength ofthe laser light, there will be aphase difference between lightreflected from a pit and thatreflected from the aluminiumlayer of 2414=180° (in an idealcase). This means that due tothe interference effect the tworeflected light beams willcancel one another. In practice,this cancellation will not becomplete, however, but the re-duction in the total reflectedlight is none the less sufficientto actuate the focusing detector

unit. The reflected light isconsequently modulated in amanner that depends on thelength of the pit.

The optical systemThe laser, optical system, anddetector are contained in oneunit as shown in Fig. 7. The col-lection and telescope lensassemblies focus the lightemanating from the laser diode.The correction prisms shapethis to an annular beam. Thisbeam is deflected by a routeingmirror assembly to a polarizingbeamsplitter and 1/4 plate as-sembly, where the plane ofpolarization is shifted by 90°.From there, the beam passesthrough the objective lens tothe recording surface of the CD.The reflected light is taken fromthe objective lens, alignedparallel, and then falls onto theA/4 plate. The plane of polariz-ation is again shifted 90°, afterwhich the beamsplitter directsthe beam to the focus errorprism, from where it travels tothe detector (photo -sensor).

7

'FOCUS ERROR PRISM

DETECTOR

COLLECTION LENS r21ASSEMBLY

\\.\\TELESCOPE LENSASSEMBLY 131

LASER DIODE 111

OBJECTIVE LENSTWO AXIS Ill

ACTUATOR

CORRECTIONPRISMS 14/

POLARIZINGBEABSPLITTER/XI PLATEASSEMBLY WI

ROLPEING MIRROR ASSEMBLY 151

Fig. 7. Cross-sectional view of a typical laser pick-up unit.

8Objective lens

Polarizing prism(beam splittor)

Diffraction grating

Laser diode

To disc

Shaft

Focus movement -LTwo - axisTracking movement -1- device

Magnet

1/4 wave plate

Collimation lens

Cylindrical lensfor focus system

Pholosensor

Fig. 8. The SONY laser pick-up unit.

In the Sony laser head used incommercial CD players, shownin Fig. 8, the photo -sensor is afour -quadrant type. This headcontains two extra sensors (Eand F) for the side spots. Con-trol signals from these sensorsdrive the two -axis device.Input signals for the audioamplifiers, servo systems, andassociated circuits in the com-pact disc player are also takenfrom the photo -sensor unit.

Sampling frequencyThe sampling frequency shouldbe greater than twice the fre-quency of the highest audio fre-quency the system is requiredto process. Taking also the anti-aliasing requirement into ac-count, a world-wide standard of

44.1 kHz was chosen.With a sampling frequency of44.1 kHz, the upper audio fre-quency range must be limitedto just above 20 kHz. Althoughthis is considered satisfactoryby many, there are also manywho feel that this limitation isunacceptable. Since manufac-turers of CD players can notchange the agreed samplingfrequency, they have devel-oped a technique called digitalfiltering or oversampling.In oversampling, the originalsampling frequency is seem-ingly doubled or even quad-rupled by electronic means. Intwice oversampling, there are44,100 real samples coming offthe disc, and a special elec-tronic circuit adds a sample be-tween each pair of real ones togive a total of 88,200 samples.

41 EE

JulyiAugust 1987

These added samples are anelectronic prediction as to whatthey would have been had theybeen recorded on the disc.In four times oversampling, thenumber of predicted samplesincreases to three betweeneach pair of real ones. In someCD players, the previous thirtysamples are used to predictevery set of three guessedsamples.With all oversampling, extrabits are generated: one in twiceoversampling, and two in fourtimes oversampling. These bitsare in addition to the 16 bitsalready coming from the disc.Unfortunately, the signal pro-cessing circuits of CD playerscan cope with 16 bits only, sothat. ironically, some of the in-formation has to be discarded.

Although CDs are fullyprotected from dust andsoiling, it is, none the less,necessary to clean them fromtime to time. One of the bestways to do this is with theBIB Compact Disc Cleaner kit.The kit contains a foam -linedmoulded tray in which the CDis held, cleaning fluid, a softbrush to remove dust, a feltcleaning pad, and a chamoisleather to dry and polish thedisc. Available from mostaudio retailers or direct fromBIB Audio Video Products Ltd Kelsey House Wood LaneEnd HEMEL HEMPSTEADHP2 4RQ telephone (0442)61291.

Aliasing is a type of interferencethat occurs when the frequencyof the signal to be sampled isequal to or greater than half thesampling frequency.

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July'August 1987

Disc productionAt present, there are only adozen or so CD producers inthe western world and two inthe USSR. Most of these madetheir name through gramo-phone record production andhave been in existence for along time.The largest CD producer is cur-rently PolyGram, a subsidiary ofPhilips, with plants in FederalGermany and Britain. The firstBritish company to produceCDs was Nimbus of Monmouth,which started in 1984. There isnow also Thorn -EMI in Swin-don. Since worldwide pro-duction at present amounts toonly about 100 million per year,it is clear that with nearly 20million CD players in use in thewestern world demand out-strips supply, which will keepthe price of the disc high. It willtake a year or so yet beforesupply will start catching upwith demand: only then is therea likelihood of CD prices com-ing down from their presentlevel.The biggest bottleneck in pro-duction is the metallization ofthe disc with aluminium whichensures that the disc can beread by the laser in the player.Until recently, this was done inlarge chambers that hold hun-dreds of discs at a time. It takesabout 15 minutes to create avacuum in the chamber andanother 10 minutes to depositthe aluminium. New machinesfrom Balzer in Switzerland bringthe cycling time down by morethan a half. These evaporationchambers are held at a perma-nent vacuum. The discs areloaded at one end on a con-veyor and passed through aseries of bulkheads that createa pressure gradient from at-mospheric to high vacuum andup to atmospheric again.

42

In spite of the strict clean -roomprocedures at CD productionplants (in most the disc does notcome into contact with humansuntil it has been given the pro-tective lacquer coating: allprevious operations are per-formed by robots), the rejectionrate remains high at over 10%over the entire production pro-cess. It should, of course, berealized that this involves nofewer than 60 stages from tapemastering, through disc mas-tering, electroplating, pressing,metallization, and so on, topackaging.An interesting aspect of thesiting of a CD production plantis that the foundations must bevery stable: deep rock is pre-ferred, because its naturalmovement is not more than afew micrometres at very low fre-quency. This stability require-ment becomes clear when it isrealized that the track dimen-sions of the high density masterdiscs are less than 1 micro -metre.

The CD videoDuring the preparation of thisarticle, Philips, Sony, and anumber of other Japanesemanufacturers announced theCDV player. This type of player,whose commercial launchis planned for the comingautumn, can handle normalaudio compact discs as well asthe new CDV discs which hold5 minutes of colour video aswell as 20 minutes of soundonly.It appears these manufacturers'intention to use CDV as a meansof marketing pop music videoclips. Polygram, Philips' sub-sidiary record, CD, and tapemanufacturing plant in FederalGermany, is in full support ofthe new system, and claims that

most of the world's large recordcompanies have confirmedtheir backing.The video picture signal isrecorded towards the outeredge of the disc, where it iseasier to get a high trackingspeed. Normally, a digital audiodisc spins between 196 and 486rev/min to give a constant linearvelocity (laser tracking speed)of 1.2 m/s. This is too slow evenfor analogue video.The snag with the new system isthat it is linked to TV standards,at least as far as the video sec-tion is concerned. For PAL CDVdiscs, with 25 pictures/s, therotational speed varies from1512 to 2250 rev/min, givingit a CLV of between 9.2 and10.2 m/s. For NTSC video (30pictures/s), the spinning speedwill be 1815 to 2700 rev/min,resulting in a laser trackingspeed of between 11 and12 m/s.

Commercial aspectsDuring the 1980s, the audioequipment market in generalgrew moderately in size, buthardly at all in value. The excep-tion was the CD player sector,which saw a boom towards theend of last year that continuedinto this year. An estimated192,000 players were sold in

November and Decemberalone: a three -fold increasecompared with the samemonths in 1985. If these newbuyers follow their prede-cessors' purchasing patterns,the sale of CDs should risequite sharply. GramophoneMagazine's CD survey showedthat 69% of CD player ownersown more than 20 discs. How-ever, although compact discsoffer hitherto unattainable qual-ity, at nearly twice the price ofLPs and cassettes they still ap-peal mainly to the seriousmusic enthusiast.Figures just released by theBritish Radio & ElectronicEquipment Manufacturers' As-sociation (see Table) show thatduring last year CD playerdeliveries were at more thanfour times the level achieved in1985. The major development in1986 was the increasing avail-ability of combination products,primarily CD music centres,which contributed to a highlevel of consumer interest.These products accounted forover one tenth of total musiccentre deliveries. The CDseparates sector was very ac-tive and registered a more thanthree -fold increase over the1985 results. These representfaster growth than that achievedby any other consumer elec-tronics product.

Table 1

Separates Combinations Total Deliveries

1985 1986 1985 1986 1985 1986

01 16 64 8 16 72

02 20 96 24 20 120

Q3 33 158 64 33 22204 78 165 60 78 225

147 483 NIA 156 147 639

The figures show quantities in thousands.

CD players and manufacturersThere are some 150 manufacturing plants in the world licensed toproduce compact disc players. It is, of course, not possible to listall of them and some of their products, so that only the 20 -odd best-known have been selected (with apologies to the others!).

AKAI (UK) LTDUnit 12Haslemere Heathrow EstateSilver Jubilee WayHOUNSLOW TW4 6NFTelephone: 01-897 6338Akai produce a number of players in the price range £220-425.Three of the players use a 3 -beam diode -laser, and one, the CD -A70comes complete with infra -red remote control. Fig. 9. The AKAI Type CD -A30 CD player.

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July/August 1987

ALLIED INTERNATIONALP 0 Box 1487RICHMOND, IN 47375 USAUK Distributors:INCOMTEL LTD225 Goldhawk RoadLONDON W12 8SBTelephone: 01-743 5511Allied International's AMCDS-1000A programmable CD playerholds 100 CDs, features automatic random access to disc, and isequipped with a main microprocessor for system control and a sec-ondary microprocessor for CD playback operations. Intended pri-marily for commercial and broadcasting applications.

BANG & OLUFSEN (UK) LTDEastbrook RoadGLOUCESTER GL4 7DETelephone: (0452) 21591Well-known for their high -quality audio products, Bang & Olufsenproduce two CD players, the CDX at £435 SRP, and the CD50 at£576 SRP. They also make a beautiful combination unit, theBeocenter 9000, which contains an FM/AM tuner with automaticstation search, a fully automatic cassette recorder, and a latest -generation compact disc player. The SRP of the 9000 is £1,296.

Fig. 10. Bang Et Olufsen's Beocenter 9000 with the operatingpanels open.

CAMBRIDGE AUDIO SYSTEMS INTERNATIONAL LTDHome FarmDiddingtonCAMBRIDGESHIRE PE18 9XUTelephone: (0480) 811711For some time now, Cambridge's CD1 CD player has probablybeen the very top-quality player on the market. With 18 -bit D -A con-version, 4 times oversampling, a S/N ratio (weighted) of 120 dB,cross -talk between channels of 115 dB at 1 kHz and 100 dB at 20 kHz;a linearity of within 0.2 dB from 0 to 60 dB, that is not surprising. TheSRP of about £1500 is, however, probably a little high for the averagehousehold.Cambridge have also recently introduced the CD2 player, which,

Fig. 11. The top -of -the -range Type CD2 player from CambridgeAudio Systems.

in contrast to the CD1's 18 -bit, 4 times oversampling technology, isthe first player in the world to feature 16 -bit x16 times oversampling.

DENONNIPPON COLUMBIA CO LTD14-14 Akasaka 4-chomeMinatoTOKYO 107UK distributors:HAYDEN LABORATORIES LTDChiltern HillCHALFONT ST PETER SL9 9UGTelephone: (0753) 888447Denon produces professional broadcasting and studio recordingequipment as well as consumer audio products. Their range of CDplayers comprises the DCD-300, the DCD-500, the DCD-900, andthe DCD-1500. The Denon machines have always been known fortheir mechanical soundness and good quality sound.

Fig. 12. DENON's DCD-900 CD player and associated IR remotecontrol unit.

HITACHI SALES (UK) LTDHitachi HouseStation RoadHAYES UB3 4DRTelephone: 01-848 8787Hitachi produce four quality disc players, from the impressive, fullyprogrammable DAD -005 (with infra -red remote control) to theDA5000 and DA6000, and the new DA400.

Fig. 13. HITACHI's new CD player Type DAD -005 and its IRremote control unit.

PVC (UK) LTD6-8 Priestley WayEldonwall Trading EstateStaples CornerLONDON NW2 7AFJVC is one of the select band of manufacturers that produce a port-able CD player. Their XL-R1OK is one of the few personal playerscurrently available; it is priced at about £250. Additionally, thecompany offers a range of six separates, all fitted with JVC's own3 -beam laser pick-up.

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July/August 1987

MARANTZ AUDIO (UK) LTD15-16 Saxon Way Industrial EstateMoor LaneHARMONDSWORTH UB7 OLWTelephone: 01-897 6633In addition to their already impressive range of CD players (all pro-viding 4 times oversampling), Marantz have just introduced theCD94. This player is built around a non-magnetic aluminium chassisand also has a solid aluminium top cover. It has full infra -red remotecontrol, FTS, 20 -track programming and variable headphone out-put, and its digital output is available in both optical and conven-tional form. The optical form allows connection to the unit with totalelectrical isolation. The CD94 has a SRP of £799; other prices in theMarantz range are: CD45 - £199; CD56 - £249; and CD65 - £349.

44

14

Fig. 14. The recently announced CD94 Compact Disc Player fromMARANTZ.

MERIDIANBOOTHROYD STUART LTD13 Clifton RoadHUNTINGDON PE18 7BRTelephone: (0480) 57339One of only a small number of British CD player manufacturers,Meridian have earned a reputation as the leading designers andmanufacturers of the world's finest sounding compact disc players.Their latest player. the 207 -PRO (shown in the photograph with the201 preamplifier, 209 remote control unit, 204 FM tuner, and M30 ac-tive loudspeaker) has 14 -bit D -A conversion with 4 times over -sampling. Recommended prices are: CD94 - £850; 201 - £495; 209- £69; 204 - £450; and M30 - £725.

Fig. 15. The MERIDIAN Type 207 -PRO player and ancillary equip-ment lsee text above).

MITSUBISHI ELECTRIC UK LTDHertford PlaceMaple CrossRICKMANSWORTH WD3 2BJTelephone: (0923) 770000One of the few companies (so far) to offer a multi -play CD player,the DP409R, which has a capacity for loading 5 CDs that are selec-ted automatically. Complete with full infra -red remote control, theDr409R has a SRP of £329. Other players in the range include theDP107 (E199); DP209R (E249 with IR remote control); and the midi -sized DP603 (E199).

16

.,111MIEE

Fig. 16. MITSUBISHI's multi -play CD player Type DP209R canload 5 CDs that can then be selected automatically.

NAD ELECTRONICSCousteau HouseGreycaine RoadWATFORD WD2 4SBTelephone: (0923) 26499Sold throughout the world, NAD products are well-known for theirsophisticated engineering, excellent sound reproduction, and ex-cellent price -performance value. The company produces a fine CDplayer that is available in two models: the 5355 at a SRP of £399 andthe 5355E (E329).

NAKAMICHI B&W UK LTDMarlborough RoadChurchill Industrial EstateLANSING BN15 8TRTelephone: (0903) 750750The two CD players produced by this well-known company aredefinitely top -of -the -range. Unlike most other CD players, theNakamichi models use a separate D -A converter for each channelto prevent frequency-ctependent phase error. Moreover, left- andright-hand samples are separated while the signals are still indigital form so that the de -interleaving switch does not introducenoise and distortion as in a conventional player. Recommendedprices are £795 for the OMS-5E and £1195 for the OMS-7E.

PHILIPS CONSUMER ELECTRONICSCity House42-430 London RoadCROYDON CR9 3QRTelephone: 01-686 2166As would be expected, Philips is one of the very few companiesthat offers not only mains -operated CD players, but also a battery -operated personal model, and a model that can be connected toany car tuner -cassette player. Top of the range is the CD650, whichoffers 16 -bit D -A conversion with quadruple oversampling, FTS(favourite track selection), and infra -red remote control. It is pricedat £399. The CD10 portable player is priced at about £220, and theType DC085 car model at about £300.

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July/August 1987

PIONEER HIGH FIDELITY (GB) LTDField WayGREENFORD UB6 811ZTelephone: 01-575 5757Recent additions to an already impressive range of CD players arethe PD -M60 and PD -M70, both multi -play models. This means thatPioneer can now offer no fewer than three players that can load upto six discs at a time. These can be played back one by one, or inorder of (preset) choice, or at random. Both the new players haveinfra -red remote control: that of the PD -M70 is very interesting inthat it has its own memory, enabling the storage of up to 8 separateprogramming sequences, and its own volume control, whichoperates in the digital circuits. The company also offer a portableplayer, the PD -C7 (BK) and two models intended for installation ina car: the CDX-1 and the CDX-Pl.

Fig. 17. PIONEER's PD -M70 is a multi -play CD player that canload up to six CDs at a time.

SANYO MARUBENI (UK) LTDSanyo HouseOtterspool WayWATFORD WD2 8JXTelephone: (0923) 46363The three players in Sanyo's range, CP08, CP500, and CP667, all fallin what may be termed the budget range: £199-299. There is also agood -value -for -money portable player, the CP10 at about £270.

SONY (UK) LTDSony HouseSouth StreetSTAINES TW18 4PFTelephone: (0784) 61688This giant of the compact disc world has no fewer than elevenplayers in its range, at prices from £200-700. The range includes twoportable models: the Discman D55T at about £300, and the Discman50 at around £260. The portables are smaller than the average hand-bag and probably lighter than most of those.

TANDBERGTAN AUDIO (UK) LTDP 0 Box 31CHICHESTER P020 7RXTelephone: (0243) 56342Norwegian audio equipment specialist Tandberg produces onlyone CD player, but this is of the highest quality. The TCP3015A,priced at about £1,100, offers 4 times oversampling, flat phaseresponse, separate headphone amplifier, full programmability, andfull infra -red remote control.

TECHNICSPANASONIC UK LTD300-318 Bath RoadSLOUGH SL1 6JBTelephone: (0753) 34522The Technics range of CD players includes a professional model,the SL -P1200 at about £800, a portable, the SL-XP5 at around £290,and six mains -operated models, four of which with full infra -redremote control. The separates range in price from just over £200 tojust under £400.

TOSHIBA UK LTDToshiba HouseFrimley RoadCAMBERLEY GU16 5JJTelephone: (0276) 62222Toshiba's range of CD players falls entirely in the budget range ofprices (up to about £300). and includes the cheapest model cur-rently available in the UK; the XR-J9 at £159. The company also offersa portable, the XR-P9RC, which must be just about the best portableavailable at present. Priced at £259, it is unique in being suppliedwith full infra -red remote control.

YAMAHA ELECTRONICS (UK) LTDYamaha House200 Rickmansworth RoadWATFORD WD1 7JSTelephone: (0923) 33166World-renowned audio/music specialists Yamaha have an in-teresting range of six CD players, ranging in price from about £250to around £600. Most of these are offered with remote control, andall of them are fitted with a floating suspension to minimize shocksand vibrations being transmitted to the laser pick-up. Moreover, allplayers are fitted with dual cyclic redundancy check code-CIRC-and error correction system.

Fig. 18. The CD -X3 Natural Sound Compact Disc Player fromYAMAHA.

Some other usefulCBS RECORDS17-19 Soho SquareLONDON W1Telephone: 01-734 8181

DECCA RECORDS15 Saint George StreetLONDON W1A 2BRTelephone: 01-499 0422

addresses.

DEUTSCHE GRAMMOPHON15 Saint George StreetLONDON W1A 2BRTelephone: 01-499 0422

EMI RECORDSThe QuadrangleWest Mount CentreUxbridge RoadHAYES UB4 OHBTelephone: 01-848 3611

MOBILE FIDELITY SOUNDLAB1260 Holm RoadPETALUMA, CA94952-1182USATelephone: (707) 778-0134

NIMBUS RECORDS LTDWyastone LeysMONMOUTH NP5 3SRTelephone: (0600) 890682

PHILIPS RECORDS(PHONOGRAM)15 Saint George StreetLONDON W1A 2BRTelephone: 01-499 0422

POLYDOR RECORDS15 Saint George StreetLONDON W1A 2BRTelephone: 01-499 0422

POLYGRAM INTER-NATIONAL LTD45 Berkeley SquareLONDON WLX 5DBTelephone: 01-493 8800

RCA RECORDS1 Bedford AvenueLONDON WC1Telephone: 01-636 8311

EE

July/August 198746

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EDI markettakes offAfter a sluggish start, ElectronicDocument Interchange (EDI) isfinally beginning to take off. Ac-cording to Electronic Docu-ment Interchange Markets-USA and International, a newreport (#732) from InternationalResource Development, themarket will grow from just over$80 million this year to over $1billion by 1994.Third -party service suppliers,providing VAN services for EDI(which include protocol con-version, validity checking, bat-ching, etc.) will be the majorbeneficiaries of this growth.Current leaders includeMcDonnell Douglas, GeneralElectric, and Transettlements,while the IBM Information Net-work service is a fast-growingcontender.According to the report, thestandardized nature of the EDImessages, and the fact thatthey must be transmitted overgovernment -controlled PTTtransmission facilities will in-evitably attract a tax on docu-ment transfer in someEuropean and Third Worldcountries.

Granada/HTEdeal apromising onefor the puntersGranada Business Systems Div-ision has placed a contractworth £41/z million with com-puter specialist High Tech-nology Electronics.

The contract is for viewdatacomputers to which softwareTV monitors will be added byGranada Business Services Div-ision. The equipment will formpart of the new satellite audio,text and visual service forBritain's bookmakers which hasbeen developed by Satellite In-formation Services nationwide.

LAN faultsimulationA unique Local Area Networkfault simulation accelerationcapability from HHB Europewas announced during theBritish Electronics Week.Known as LANA (Local AreaNetwork Acceleration), thiscapability reduces the cost ofsimulation by integrating ac-celerated simulation into exist-ing workstation environmentswithout the major investment ofan acceleration engine.The LAN extension to CADATallows a single workstation tocommand the distribution ofthe fault simulation task to multi-ple CPUs over Ethernet.A CADAT user on any work-station could initiate a faultsimulation and elect to request"service" from any number ofother LANA equipped worksta-tions. The LANA software auto-matically checks the availabilityof each, and dynamically con-figures the task to fit the cur-rently available resources.LANA is "intelligent" enough todetect if a SERVER goes off-lineand reconfigures the tasks "onthe fly" to handle the new con-ditions. LANA fault simulationscan be run interactively orunder "batch processing"control.

Six thousandvisitorsexpected atAPRS showMore than 6000 visitors fromBritain and overseas are ex-pected by the organizer to at-tend the international APRS*Exhibition for the professionalaudio market at London's Olym-pia 2 exhibition centre from 24to 26 June 1987.Now in its twentieth successiveyear, the show has been over-subcribed since before the endof January. There will be 150stands on two floors occupyinga total net display area of3000 m2.This year's show catalogue willinclude for the first time thenames of manufacturers whoseproducts are being shown onthe stand of agents. These willbe cross-referenced to theagent's stand number so thatvisitors will be able easily tocheck the entire range of prod-ucts being shown.* Association of ProfessionalRecording Studios Limited o163A High StreetRICKMANSWORTH WD3 LAY.

British Telecombacks elec-tronic paymentsBritish Telecom has declared itscontinued support to Britain'sfinancial institutions andretailers in bringing a fullyautomated system of cashlesspayments to shops, stores andother retail outlets throughoutthe country.National introduction of thesystem, known as electronicfunds transfer at the point ofsale (EFTPOS), is scheduled tobegin towards the end of 1988.EFTPOS is an automatedpayments systems designed totransfer value from purchaser toseller more conveniently and atsimilar or less cost than forpayments by' cash, cheque orcredit card.The system will enable the

financial institutions to containor even reduce costs and tomanage the increasing volumeof transactions more efficiently.It will also enable them to de-velop a new range of elec-tronically delivered services.The concept currently beingconsidered involves a plasticdebit card which, in conjunc-tion with a signature or per-sonal identification number(PIN), identifies the card user.Payment is made by wiping thecard through a slot in the EFT-POS terminal at the point -of -sale, entering details of the pur-chase, obtaining PIN orsignature verification from thecustomer, and in most cases ob-taining authorisation from thecard issuer's computer over anon-line connection. Finally, set-tlement takes place betweenthe purchaser's and retailer'sbanks.

3Comannouncessupport for newIBM computers3Com Corporation is sup-porting IBM's PersonalSystem/2 series of computers,providing network operatingsoftware and network interfacesthat allow the new machines tobe integrated into existing3System workgroup systems.Currently, there are about300,000 3Com -adapted personalcomputers on 30,000 3Com net-works worldwide. 3Com pro-vides Ethernet, Token Ring andAppleTalk connectivity.3Com is modifying its 3+ net-work software to work underDOS 3.3, ensuring compatibilitywith current Personal Systems/2machines and IBM's new TokenRing adapter for its Micro Chan-nel architecture.3Com's newest version of its 3+network software (version 1.2)will work with DOS 3.3 and sup-port the new IBM Token Ringadapter. In addition to the tra-ditional 5.25 -inch format, 3+will be offered in the 3.5 -inchfloppy disk format required bythe new computers.

EE

July/August 1987

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TELECOMMUNICATIONS TELECOMConference onrural communi-cationsThe Institution of ElectricalEngineers (IEE) is to hold an In-ternational Conference onRural Telecommunications atthe IEE, Savoy Place, LondonWC2, from 23 - 25 May 1988.The Conference will considerthe ways of providing moderntelecommunication services tothe world's rural communitiesby means of appropriatemodern telecommunicationtechnology.Cost effective provision and op-eration of rural telecommuni-cations systems continue topresent major difficulties forthe telecommunicationsengineer. The problem is notconfined solely to the develop-ing world. Most rural telecom-munications services indeveloped countries run at aloss and need to be supportedby cross subsidy from moreprofitable city and urbanservices.This situation is, however,changing. Privatization andcompetition requiring high pro-fitability and efficiency makecross subsidy unattractive. This,coupled with the regulatory re-quirement to continue pro-viding services to ruralcommunicaties, is creating theincentive to find new ap-proaches to the provision andoperation of rural telecommuni-cations. In developing

countries the scope for crosssubsidy is often very limitedarid rural telecommunicationsconsequently very restricted.The need is again for moreeconomic solutions to befound.Technological developmentsparticularly in the fibre opticradio, and satellite fields offerthe prospect of new, more costeffective solutions. In addition,with main network digitizationwell advanced in manydeveloped countries, there is apressing need for industry tofind new outlets for the future.Considering that approximatelytwo thirds of the world's popula-tion live in rural areas and areprovided, for the most part,with indifferent telecommuni-cation services, the marketrepresented by rural telecom-munications is potentially verylarge.

Racal com-munications forAtlanticballoonchallengeAccurate and reliable com-munication and navigation sys-tems will play a key role in theforthcoming attempt to makethe first crossing of the Atlanticocean by hot-air balloon.As with Don Cameron's near

xi 0 at cir id cidOciaketai.ci

- - - _ .

A high -capacity switching matrix specially designed for therouteing of digital remote control signals is available from CALMedia Systems o Cox House o Amberley Way o HOUNSLOW11N4 6BH.

successful attempt to cross theAtlantic by helium balloon in1978, Racal Electronics is again

-providing high technologycommunications and navigationequipment. Racal will also setup and operate the vital controlcentre at one of its UR locationsin the Thames Valley.Towards the end of the flight,Cameron and Howard will needto know their location withgreat accuracy so that they canmake the critical decision to re-lease themselves from the largeballoon at the right time. For thisreason, they will be carrying aRacal-Decca DYN IV (DeccaYacht Navigator) which plots itsposition by using the world-wide Decca radio navigationsystem.During the preparation periodfor the attempt, the balloonteam will be supplied withRacal-Vodafone cellular tele-phones to enable them to keepin touch at all times, especiallyduring trials when the teamwill be in remote parts of thecountry.

BT an NTTexpandrelationschipBritish Telecom and NipponTelegraph and Telephone Cor-poration (NTT) have signed amemorandum on collaborationfor the exchange of personneland information over a three-year period from April 7, 1987.The memorandum representsan expansion of exchanges be-tween the two telecommuni-cations leaders which havebeen taking place over manyyears. The new relationship in-cludes mutual exchanges ofpersonnel and reciprocal visitsby executives and middlemanagers, plus the sharing ofbusiness experiences after theprivatisation of the twocompanies.The plan is designed to pro-mote increased business ac-tivities of both firms.

Incomtel forSamoaThe London - based Incomtelsystems engineering grouphave won a major contract forthe expansion of existingfacilities at the Western SamoaPost Office Satellite EarthStation near Apia.The contract has been awardedto Incomtel by the South PacificBureau for Economic Co-operation and will be funded bythe European Developmentfund. A large proportion of thecontract will be completed atIncomtel's well equipped testcomplex, in their West Londonheadquarters, prior to ship-ment.Incomtel will be responsiblefor the supply, installation andcommissioning of the entiresystem interfacing with theexisting single channel per car-rier service. The upgrading ofthe earth station will be ef-fected by the introduction ofcompared frequency divisionmultiplex services with NewZealand.In addition to this expansionprogramme, Incomtel's contractwill also include the upgradingof the system at the Apia tele-phone exchange. This includessupervisory and engineeringservice circuit facilities.

Marconi Radarwins majorPlessey orderMarconi Radar Systems Ltd(Gateshead) is to supply ap-proximately 100 'Isolator'mobile shelters to PlesseyMilitary Communications to aidits fulfilment of the MOD con-tract for the Home DefenceRadio System (HDRS).The Isolator range is designedspecifically to provide a protec-tive environment for sensitiveelectronic equipment. The con-tract calls for the lightweightshelters for use with smallprime movers - Landrover GSvehicles and fighting vehicletrailers.

EE

July/August 1987

TELECOMMUNICATIONS TELECOM1N3Com tolicence Micro-soft's OS/2 LANManagerproducts3Com Corporation is licencingMicrosoft Corporation's newmultitasking network operatingsystem, MS OS/2.Its IBM-compatible networkoperating software, 3+, isbased in part on the currentMicrosoft networking system(MS -Networks). The new gener-ation of Microsoft products,which will be integrated intofuture releases of the 3Comproducts, will allow higher per-formance and a broader rangeof capabilities.

BT UK Com-municationsDivisionBritsh Telecom have created anew division by merging its In-land Communications andBusiness Services Divisions.The new division is called theUK Communications Divisionand is headed by Mr Mike Ben,until the merger ManagingDirector of Inland Communi-cations. Within the new divisionMr Nick Kane will serve asDirector, Customer Marketing,while Dr Sydney O'Hara will beDirector, Products andServices.

When telecommunications cables are lowered from ship to oceandepths, tension can build up on their fabric. This high-speedstranding machine ensures they reach the ocean floor in goodcondition by adding two contra -directional layers of torsionallybalanced high tensile steel wires to the cable to give the tensilestrength so necessary in laying or recovery operations.The machine is one of a number recently installed at the STCfactory in Southampton, where it will contribute to thecompletion of orders for optical fibre systems currently in hand,including the UK to Denmark link and part of the firsttransatlantic optical fibre system TAT -8.Traditionally subsea links have used coaxial cables, principallycarrying analogue traffic with capacities up to 5520 telephone cir-cuits. Now submarine telecommunications use optical fibre cablecontaining hair -thin strands of glass that carry digital traffic bymeans of light with much greater carrying capacities.STC has supplied more than half the undersea telecommuni-cations systems in the world, including nearly 200 000kms ofcable and 9000 repeaters - amplifiers that are spliced into thecable at intervals to boost the signal. The company also suppliedthe world's first international underwater optical fibre system in1986 between the UK and Belgium. It can carry at least 11 520 cir-cuits for telephone, facsimile and data traffic. This basic capacitycan be increased up to three times through the use of specialequipment in the terminal stations.

Cashlessphoninggathersmomentum inEuropeCoin and cashless calls frompayphones in seven Europeancountries are set to becomeeasier following the recentaward of contracts totalling £10million to Plessey Telecom-munications Products.Systems chosen range from "in-telligent" payphones equippedwith telemetry sensors whichcan alert a central control pointof faults, vandalism and coin ca-pacity, to those in which creditcards, prepaid phone -cardsand verbally -communicatedpersonal identification num-bers can be given to an oper-ator.Televerket of Sweden chose thePlessey credit card system fol-lowingtrial at Stockholm's Arlanda Air-port. Telefonica of Spain isworking closely with Plessey todevelop both a coin and creditcard system. This includes averbal software package inwhich the caller is advised ineither Spanish or English howto proceed and insert cardswhich are "read" by the instal-lation for future billing.In the wake of these successesthe Finnish FIT has invitedPlessey to install a field trial of asimilar credit card system.Plessey is already supplying itsrange of "intelligent" coin -phones to Finland, Denmark,Spain and Cyprus. Cardphonesfrom Plessey have also beenordered or are on trial in Den-mark, Norway and the Republicof Ireland.A contract has been awardedby British Telecom for the de-velopment of systems thatenable a caller to have chargestransferred to his home orbusiness account when usingeither a public box or anotherperson's private phone. Thiswill be done by transmitting apersonal identification numberknown only' to the caller to anaccounting point. Thesecashless services processor

units will be available bymid -1988.

Three methods of card paymentare currently being used.These may be internationalcredit cards such as Amex, Ac-cess, Diners or Visa. The sec-ond category is cards issued bynational telecommunicationsauthorities. At the end of a callthe cost is displayed by thephone and then relayed to thecredit card billing centre for in-clusion on standard monthlystatements. The third memberof the cashless payphone familyis the pre -paid payphone cardwhich can be bought from postoffices and shops.Referring to the recent exportorders valued at £10 million,Plessey Telecoms managingdirector Mr Peter Brown saidthat three European countries- Spain, Sweden and Britain -were now leading the world inimplementing credit and ac-count call payphone tech-nology, and in each countryPlessey was supplying thesystem.

Call for papersA call for papers has beenissued by the organizer of theFourth International Con-ference on High FrequencyRadio Systems and Techniquesto be held in London from 11 to13 April 1988.The aim of the conference, ex-plains the organizer - the Insti-tution of Electrical Engineers -is to bring together and focuspresentations on recent ad-vances in the theory, design,performance and operation ofHF communications systemsand networks, and to provide adiscussion forum for resear-chers, designers, manufac-turers, users and other workersin the field.Offers of contribution are in-vited on any theoretical or prac-tical aspects of HFcommunication and other radiosystems. Further informationfrom: Conference Services oThe Institution of ElectricalEngineers a Savoy Place oLONDON WC2R OBL.

EE

July/August 1987

TELECOMMUNICATIONS TELECOMIAcron PALencoderTwo Acron model 606P colourencoders are now being usedby London Weekend Televisionas part of a novel system for dis-tribution of ITV network pro-gramme information to otherindependent television com-panies.The information system, knownas 'NETFAX', is located in theMaster Control area, and isbased on three BBC Microcom-puters, which output thealphanumeric and graphicsdata in the form of RGB signals.These are encoded to PAL bythe Acron units for transmissionas part of the Company's net-work material.This method of communicationis a particularly convenient wayof passing scheduling detailsand similar information to therecipients of network program-mes, obviating the need forseparate communication chan-nels. In practice the informationis entered to the computermemory on "scratch -pad" basisfor transmission when appro-priate, the formatting data, identheadings etc. being held onfloppy disc. Transmission is in-itiated by simple manual com-mand to the computer.

Statusline forHTE

Contec's Statusline has been ac-quired, and will continue to besupported, by High TechnologyElectronics.The acquisition confirms HTE'scommitment to the telecom-munications industry and marksa new initiative in productdiversification triggered by thecompany's takeover by AlanPatricof Associates. The entireStatusline team, including de-velopment, manufacturing,sales and service personnel,has been retained by HTE andwill continue to operate in theBasildon area and through theexisting distribution network.Statusline was conceived abouttwo years ago and has achieved

widespread popularity. Thecost-effective system fills thegap in manager/secretary com-munications brought about bythe absence of a visual indi-cation of telephone line statusin modern PABX systems. Ituses single or multiple lampdisplays to allow the secretaryto monitor the status of one ofup to ten lines, making more ef-ficient use of the many valuablefeatures of the new exchanges.

Barry Brinkman: HTE andPatricoff will continue to takethe initiative in support for thetelecommunications industry.

Gentech-ThetaJ agreementTelecommunications relaymanufacturers Gentech Inter-national Ltd have been ap-pointed distributors for theMOSFET-based range oftelecom solid state switchingdevices manufactured by theTheta -J Corporation of America.The MOSFET-based design ofTheta -I solid state switches andrelays is ideal for switching andcontrol of telecommunicationcircuits and is suitable for DC orAC loads up to severalmegahertz. The high input im-pedance and low input drivevoltage dramatically reduce theminimum input power requiredfor operation.

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European DataCommuni-cations MarketThe United Kingdom will re-main the largest data communi-cations equipment market inEurope, followed closely byFrance, but Federal Germanywill be the fastest growing ofthe three. These are the fin-dings of a two -volume report(#E828) just published by Frost& Sullivan. The report predictsthat the market will grow from$835 million in 1987 to morethan $1.1 billion in 1990.The UK's partly privatized andenthusiastic British Telecom isgiven much credit for keepingdata communications chargeslow in Britain. The UK con-situtes by far the largest com-puter market relative to its GNPin Europe and this creates a de-mand of 30% of the totalEuropean market for data com-munications equipment (about$227 million in 1986).France's Transac public packet -switched data network is"clearly the most widespreadand popular" in Europe: thecountry represents nearly aquarter of the European marketby value ($182 million in 1986).The highly restrictive attitude ofthe Federal German Bundes-post caused the German marketto be smaller than a tenth of theEuropean total ($72 million in1986).

According to the report,modems are, an endangeredspecies, although they will stilrepresent more than 40% of theEuropean market by value in

1990 (down from 60% in 1986). Incontrast, multiplexers are grow-ing and will account for morethan a quarter of 1990 sales. Net-work control systems will ex-pand to nearly 20%, and proto-col converters will approach10% of the total market. Low -speed modems will shrinkdramatically (by 50% a year),although RF models (for usein wideband LANs) will .risenearly as fast. Fibre optic multi-plexers will be the fastest -grow-ing of the muxes.

COBOL forXIOPENThe X/OPEN Group hasadopted Micro Focus Level IICOBOL as the basis for its stan-dard portable COBOL for UNIX.Micro Focus is a pioneer in thedevelopment of COBOL com-pilers and related programmerproductivity tools for micro-computers.The X/OPEN Group is an in-dustrial consortium consistingof AT&T, Bull, DEC, ICL,Ericsson, Hewlett Packard, Nix-dorf, Olivetti, Philips, Siemens,and UNISYS. Its objective is toestablish a Common Appli-cations Environment (CAE) tothe mutual advantage of end -users, software vendors, andcomputer suppliers. The CAEenables software to be movedeasily from one computersystem to another at a fraction ofprevious costs.

EE

July/August 198750

FILTERS:THEORY AND PRACTICE 1

by A.B. Bradshaw

The design of filters remains a topic of considerable interest topractitioners in many branches of electronics, in spite of the factthat many of such networks can nowadays be purchased at rela-

tively low prices. None the less, there are still many occasionswhen a filter has to be designed from scratch. This series of

articles will look at the theory underlying such design, and inthe last part two practical designs will be discussed in detail.

As long as there has beenelecronic engineering therehas been a need for filters: low-pass, high-pass, band-pass, andband -stop. Basically, a filter is anelectrical network that will passsignals with frequencies withincertain ranges and suppresssignals with other frequencies.A network is essentially anumber of impedances con-nected together to form asystem the behaviour of whichdepends on the values of theresistances, capacitances, andinductances from which it ismade up, and on the way inwhich they are interconnected.In the 1920s, Zobel developedthe so-called image parametertheory, which formed the foun-dation for filter and networkdesign until comparatively re-cent times. This theory met theneeds of designers working onfilters for multi -channel tele-

phone links and VF teleprinterlinks quite adequately.Television, radar, data trans-mission, and other techniquesdeveloped during the 1940s and1950s showed up the limitationsof image -parameter theory. Thehigher precision and more ex-act characteristics required offilters from then on caused theimage -parameter theory to giveway to the modern networktheory that uses synthesis tech-niques and digital computers.One of the latest products ofmodern filter technology is thesurface acoustic wave filter,which has an exciting perform-ance, and can already be ob-tained at relatively low prices.Murata, for instance, produce a10.7 MHz SAW that retails forless than £5 (available fromCirkit), and Plessey make unitsfor the IF stages in TVreceivers.

Surface acoustic wave filtershave a superb rectangular fre-quency response with constantgroup delay: it is possible tomake these filters and shapethe two features separately-this is unique to SAWs. Theironly disadvantages are a highinsertion loss (20-30 dB),which results from the necessi-ty of suppressing certain trans-mission reflective modes, andthe necessity of temperaturestabilization of the unit for cer-tain applications: there isusually a price for everything!

General networkconceptsNetworks can be shaped like aT, a TI, or art L, as shown in fig. 1.There is also a ladder networkand a lattice network. Theboxes in the diagram (and all

others in this article) representan impedance. This impedancemay be a pure resistance, areactance, or a combination ofthe two. It is customary to showseries impedances in half, i.e.Z1/2, and parallel (or shunt) im-pedances double, i.e. 2Z1. It willbe seen that this eases thecalculations.Most networks and filters areunbalanced and one side isusually grounded. A notableexception is found where highlevels of electromagnetic humor RF interference prevail. Thissituation can arise in soundstudios, particularly when theseare co -sited with their parenttransmitters. In these cir-cumstances, the sound line dis-tribution system is usuallybalanced. The balanced ar-rangement is made to cancelout induced currents in eachleg of the lines.

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Characteristicimpedance ZoThe characteristic impedance,Zo, is defined as the value of theinput impedance of an infinitenumber of cascaded identicalnetworks-see Fig. 2. From thisdefinition, it follows that a net-work with a terminating im-pedance of Zo behaves as if itwere infinitely long. Such a net-work is said to be matched-see Fig. 3.

Since the network in fig. 3 is in-finitely long, no signals canreturn from the far end. Thisreasoning also applies to a net-work matched in its own Zo. Itshould be noted that even if anetwork is not matched in itsown Zo, and contains lossy im-pedances, it can be shownmathematically that it still tendsto behave as though it were in-finitely long.

Symmetrical orasymmetricalA network is symmetrical if itsinput and output terminals canbe interchanged without caus-ing any change in its electricalperformance.A network is asymmetrical if itsinput and output terminals cannot be interchanged withoutcausing any change in its elec-trical performance.

With asymmetrical networks,two conditions are of particularinterest. In Fig. 4, an impedance

ZiC2 at one pair of terminals ofnetwork N produces a like im-pedance at the other pair of ter-minals. Similarly, an impedanceZKI at the other pair of terminalsproduces a like impedance atthe first pair of terminals. Im-pedances Zxi and ZII2 arecalled iterative impedances. Ifthe two iterative impedancesare equal, their common valueis the characteristic im-pedance of the network.

In Fig. 5, impedance Zn con-nected across one pair of ter-minals of network N causes animpedance Z12 at the secondpair of terminals, and an im-pedance Z12 connected acrossthe second pair of terminalscauses an impedance Zn at thefirst pair. These two im-pedances are called image im-pedances.In symmetrical networks, theiterative and image im-pedances are equal.

Maximum powertransfer theoremFor a generator to supply powerto a load at maximum efficiency,certain conditions must prevail.In Fig. 6, Zccjs0i is the com-plex impedance of the gener-ator and acjs02 is the complexload impedance.

The total loop impedance is

ZT=ZGCiSCOI ZI,CiS412 =

= (ZGCOSCDI ZLCOS4)2) -1-

+/(Zosineol+Msin02)

so that

ZT2 =Zo2+ZL2 +

+ 2Zoacos(0 1-02)

Now,

1= U/Z

and

P=I2ZLcosO2

[1]

where acos02 is the resistive(real) part of ZL.From this

P.racoso2

tzG2i-a2+2zGacos(co1-02)1[2]

Differentiating [2] with respectto ZL with 02 constant gives

dP/dZL =

-U2cos02(1-Zo21Z0)IZG2/Zi..+2Zocos(01-02)12

Maximum power will begenerated when (l-Zo2/ZL2)=0(when, of course, [3] itself willbe zero). Since ZL is positive,ZL=Zo.

Differentiating [2] with respectto 02 with ZL constant gives

dP/d02 =

U2ZL((ZG2 +ZL2)sin02 + 2Zoasina)i)

(ZG2 + ZL2 + 2Zoac os (0 -02))2

Maximum power transfer willtake place when dP/d02=0,which requires that

sin02 = -(2ZaLsin0i)//(Zo2 +ZL2)= -sinct)i

It is, therefore, seen that maxi-mum power transfer takesplace when the generator im-pedance and load impedanceare conjugate, that is, whentheir real parts are equal, andtheir imaginary parts (that is,phase angles) are equal inmagnitude but opposite in sign.Note that if the generator im-pedance is variable, maximumpower will tie transferred whenthe real part of ZG (that is,Zccos0i) is zero.

EE

July/August 1987

Characteristic im-pedanceSymmetrical T network. In Fig.7

Zip =ZI /2 +Zz(Z112 i-arr)11(Z2+ZI/2+ZoT) [4]

from which after cross -multiplication and makingZip = Zcrr,

Zer=f(Zi.Z2+Zi2/ 4) [5]

When the terminating outputimpedance is removed as inFig. 8,

8

Z,0 c

0 0

ZTOC =Z1/2 +Z2 [6]

When the output terminals areshort-circuited as in Fig. 9,

ZISC =ZI /2 +(Z2Zi /2)/(Z2 + Zi /2)

=(ZiZ2+Z12/ 4)422 +Zi/2) [7]

Multiplying [6] and [7] gives

(Z2 +Zi /2XZ1Z2 +Zi2/4)/

/(Z2+Zi /2)=

=Z122 +Zi2/4 =ZoT2

and

AT= AZTocZtsc) [8]

which provides a practical wayof determining the character-istic impedance of the network.

EE

July/August 1987

Symmetrical 7: network. In Fig.10,

2Zz(Zi 2Z2Z0,1(222 +Zo-)Zip

2Z2 2Z2Zo4(2Z2+Zo-.)

from which, after cross -multiplication and makingZip =Z07,

Zo,=Z1Z2//(Zaz+Zi2/4) [9]

When the output terminals ofthe n network are open- andshort-circuited, the results aresimilar to those for the T net-work, i.e.

Zo,,=,1(LorLsc) [10]

By inspection, a further relation-ship between the T and n net-works is

Zo-ZOT=ZIZ2

L network or half section. Thisasymmetrical network is ob-tained by dividing either a Tsection or a n section in half asshown in fig. 11. This seeminglytrivial operation yields somesurprising and very usefulresults. Although the half sec-tions look similar, they are notinterchangeable as regards im-pedances. Characteristic im-pedance does not apply in thecase of a half section: instead, itwill be examined in terms of itsimage impedances.

12aO

Zo,-, 2Z, zo,

In Fig. 12a,

Zoi =Zi /2 + 2Z2Zo2/(2Z2 +Zaz)

so that,

ZoiZoz + 222.Zo -(Zi /2 + 222)Zoz =

=ZIZ2 [12]

From Fig. 12b,

Zoi =2Z2(Zi/2+Zo1)/

/(2Z2 +21/2 +Zoi)

so that

ZiZo2-2Z2Zo I + (Zi /2 + 2Z2)Zoz =

=ZIZ2 [13]

Expressions [12] and [13] can beadded and subtracted from oneanother.Subtracting gives

4Z2Zot---(Zi + 4Z2)Zoz = 0

from which

Z01202 = (Z1/4 +Z2)/Z2 [14]

Adding gives

201Z:12=2'1a [15]

Combining [14] and ]15] andremoving Zoi gives

(Z1/4 +Z2)/Z2 = Zaz /Zoz

so that

Zo22=Za22/(Zi /4 + Zz) x /Z1=

=Zi2Z22/(Z)Zz+Zi2/4)

from which

Z02 = Z1Z2//(Z1Z2 + Z12/ 4) =ZOr

(from [9])

In similar fashion, it can beshown that

Z01=ZOT

The results obtained-shown inFig.13-make clear he value ofthe half section for matchingpurposes.

Note that expressions [8] and[10] are true for the two imageimpedances, but not for theiterative impedances, whichmust be determined from firstprinciples.

Propagation constantIn a finitely long cascade ofsimilar networks, the parallelelements provide current pathsback to the sending end. Thesereturn currents do not flowthrough the load terminatingthe cascade. Likewise, theseries elements cause voltagedrops along the cascade. Thenet result of these factors is thatpower is lost in the networks. Ofcourse, if the cascade is infinite-ly long, all voltages and cur-rents would have decayed tozero. This decay of, for instance,a voltage, U, is expressed by theexponential function

U=Eexp(--d)

where E is the starting voltage, yis the propagation constant, and1 is the length down thecascade. Note that when 1=0,U= E.This function is true for theratios of currents and voltagesdown the cascade, providedthis is a regular array of seriesand parallel elements.Therefore,

11 /12 =12/13=1--1/1= = exp(y) [16]

The propagation constanty=a+ffi, also called propa-gation coefficient or imagetransfer constant, is of specialsignificance in network theory.It is a complex number, ofwhich the real part, a, is calledthe alteration coefficient or im-age attentuation coefficient,and the imaginary part, 13, iscalled the phase shift coeffi-cient or the image phaseconstant./1//zexp(a) gives the amplitudevariation, whence

a = loge(/' /12) [nepers] [17]

Similarly,

11thexp(13) gives the phase be-tween the currents, whence

/3 = loge(Ii /12) [radians] [18]

One neper (Np) equals 8.686decibels (dB),

EE

July/August 1987

Summing the voltages aroundthe loop A -B -C -D in Fig. 14 gives

/exp(2y)Zi + Vexp(2y)-/exp(y1Z2-[/exp(37)--/exp(2y)1Z2= 0

which, when dividedIexp(2y) gives

[exp(y)+ exp(-y)1/2== coshy = I +Zi/2Z2 [19]

Note that when y=0, coshy =1;the hyperbolic cosine is sym-metrical about the Y axis.

by Part 2 of this article will appearin our September issue.

Complex numbersFor some readers, it may be useful to reconsider briefly theproperties of complex numbers, sometimes called complexquantities.A good way to understand complex numbers and algebraic op-erations with them is to consider that they represent a point ina plane. In the diagram, the complex number a +jb=5+3jrepresents a point P, which has the abscissa a =5 and the or-dinate b= 3. The distance of P from the coordinate centre is thehypothenuse of the right angle ONP, which is

OP= /(a2 + b2)= f(25 + 9)= 5.83

Y

M aI

I

_ .. b)c-) 1

1 1

0'11 II

NI

_

The angle 0 that OP makes with the x-axis is given by

tan 0=NP/ON =b/a= 3/5=0.6

Instead of representing a complex quantity by its rectangularcoordinates a and b in the form a+ /b, it can also be representedby its polar coordinates, i.e., the distance, r, of P from the coor-dinate centre, 0, where

r=\,r(a+b)

and the phase angle 8 between the radius r and the x-axis,where

8 = arctan (b/ a)

which is read as "the angle whose tangent is b/ a"With reference to the diagram

a =rcos8 and b = zsin8

so that the complex quantity, P= a +jb, can also be written as

P=r (cos& + jsine)

which is often abbreviated to rcis0 or rcjs8, and sometimes writ-ten as ra, which is read as "r at the angle 0".Note that mathematicians use "i" to denote the concept of ,/--1,while electrical engineers use the "j' to avoid confusion withthe use of "i" to represent an electric current. The distance r inthe diagram is called a vector by methematicians but a phasorby electrical engineers.Two complex numbers are equal only if their real and imaginaryparts are equal. If, therefore,

a+ jb=c+jd

then a=c and b=d

Consequently,

(a + )13)+(c + jd) = (a + c)+ Ab + d)

The same rule applies to the subtraction of two complexnumbers.The multiplication of complex numbers is carried out in theconventional manner, but it should be borne in mind that p=-1and, therefore, all higher powers of j can be eliminated:

P=-1 j5=j

(a +ffiXci-jd)=ac + jad + jbc + j2bd =

=(ac-bd)+Xad+bc)

and so on.

The division of complex numbers is carried out by multiplyingboth numerator and denominator of a fraction by the conjugateof the denominator. For instance, in the fraction (a +jb)/(c-i-jd),multiply both parts by (c-jd). Thus,

(a +jbXc-fd)/(c +.idXc-id)=

=[(ac+bd)+j(bc-ad)]1( +62)=

=(ac+bci)1(c2+d2)+A(bc-ad)1(c2+62)]

EE

July August 1987 54

WHERE STUDENTS MAKETHEIR OWN CHIPS

by Brian Lawrenson, Department of Physics and Electronic Engineering, University of Dundee

Electronics engineering graduates entering industry often meet difficulties intranslating theory into practice. The advanced technology of making chips is

probably one of the biggest hurdles they have to face. A Scottish university is tacklingthe problem by getting its students to turn out chips in the laboratory.

When the Irish dramatistGeorge Bernard Shaw wrote hiscondemnation of the teachingprofession, "He who can, does.He who cannot, teaches", hecame close to identifying one ofthe main difficulties in educat-ing engineering students. It liesin ensuring that the teaching oftheoretical principles is firmlyidentified with the real world ofengineering design and manu-facture.Most degree courses in elec-tronics engineering includelectures on the principles ofsemiconductor devices, ex-plaining how such componentsas transistors and diodesoperate. At the University ofDundee we have taken thisstudy one stage further: under-graduates are regularly design-ing and making silicon chips aspart of their normal project andlaboratory work.Our involvement with thisbranch of engineering beganseveral years ago because theUniversity is close to makers ofsemiconductors in centralScotland, in an area known as`Silicon Glen. When we tookpart in the usual type of organ-ised student visit to these

companies it was clear thatmany of the undergraduateswere very attracted to their hightechnology and ultra -cleanworking conditions, so weinvited a number of semicon-ductor engineers to makeregular visits to the University tocontribute to some of the lec-ture courses.From these early beginningswe have been able to set up amicroelectronics laboratorywhich has all the facilitiesneeded to design, manufactureand test silicon integrated cir-cuits. The very high capitalcosts usually associated withthis type of work have beenlargely avoided by obtainingused professional equipmentfrom industry, either by do-nation or by paying a modestamount. It has often meant thatwe have had to wait patiently forsuitable items to become avail-able and a lot of time has beenspent on repairs and modifica-tions. It has taken some 11 yearsfor the laboratory to reach itspresent level of operation.In spite of the fact that the termsilicon chip has been muchparaded by journalists andbroadcasters, relatively few

people know how the devicesoperate or how it is possible tomake something which is sosmall and yet so complex.Most chips are made from sili-con (Si), an abundant chemicalelement which has two for-tuitous properties. First, it iseasy to oxidise its surface in afurnace to produce a stablecoating of silicon dioxide glass(silica), which is an excellentelectrical insulator. Second, itis easy to change the value ofits electrical conductivity byadding relatively small amountsof either phosphorus or boron.The electric currents whichflow in silicon are due tothe movement of negatively -charged electrons (n -type Si) or,on the other hand, due to whatappear to be positively -chargedparticles known as positiveholes (p -type Si). The latterbehaviour is somewhat surpris-ing; it arises from the way inwhich electrons interact withatoms of silicon, especially inthe presence of certain othertypes of atom such as boron.The simplest active componentof an integrated circuit is theMOSFET (Metal Oxide Semi-conductor Field Effect Transis-

tor). Its structure is shownin the first diagram, wherephosphorus and boron havebeen used selectively to formregions of differing conduc-tivity and silica of varyingthickness has been used to pro-vide electrical insulation whererequired. This transistor willswitch on if an electric field iscreated below the gate elec-trode by applying a positivevoltage to it. Electrons are at-tracted into the central regionof the device and a current canthen be made to flow through itfrom the source to the draincontacts: the MOSFET is thenacting as a switch which has nomoving parts and which isactuated by electrical means.This switching property meansthat groups of transistors maybe used to transmit and processinformation presented in theform of a binary code. A com-plete digital integrated circuitmay have more than 100 000MOSFETs formed just belowthe surface of the silicon and in-terconnected by a top layer offine aluminium tracks. A mostimportant characteristic of sucha circuit is that it is fairly insen-sitive to differences in the per -

1 Source contact(aluminium)

Silica

/3-1YPesilicon

n -type silicon 5

(phosphorus diffusion) microns

Gate Drain

n -type conducting channelcreated by the applied field 87132-1

Fig. 1. Structure of the basic MOSFET (left). Application of a positive voltage V to its gate (right) switches the transistor into the 'onstage.

es EE

July/August 1987

formance of individual tran-sistor; as long as each switcheson and off, all is well.In making a chip, the details ofevery feature in one layer of itsstructure are first recorded on ahigh definition photographicplate. For instance, all of thesources and drains in the entirecircuit would appear in thephotograph as transparent rec-tangles on a black backgroundeach measuring some fivemicrometres square. Becausethe whole chip will be onlyabout five millimetres square oreven smaller, there is room onthe plate for the detail con-tained in at least 200 identicalchips, arranged on the photo-graph like a sheet of stamps.This detail is then transferredto the surface of the silicon bya process called photolitho-graphy. It means coating theoxidised surface of a thin discof silicon (called a silicon wafer)with a layer of a substanceknown as photoresist, which issensitive to ultraviolet light.Using the photographic plateand UV light produces animage of the circuit features inthe photoresist which, whentreated with acid, reveals thesource and drain regions as tinyrectangular holes in the silicaand exposes the surface of thesilicon.Manufacturing processes thatfollow include the diffusion ofboron or phosphorus throughthe holes in the silica into thesurface of the wafer, in furnacesat temperatures of about 1100°C.Finally, the whole wafer iscoated with a thin layer of alu-minium in a vacuum chamber,and photolithography etches itinto the pattern of metal trackswhich connect the transistors.The details of each layer derivefrom its particular photomask.

Fig. 2. Photomicrograph of a chip 1.8 mm square made by astudent.

Our microelectronics labora-tory is equipped for all theseprocesses, in a suite of clean -rooms with a filtered air supplyto exclude dust. It has it ownphotographic unit with camerasfor making the photomasks.One cleanroom is reserved forphotolithography and anotherfor the 10 electrically heatedfurnace tubes with their associ-ated gas supplies. The largestarea has probing equipment formaking electrical test measure-ments on the finished wafers.There is also equipment forsawing the wafers into separatechips and for mounting them intheir familiar plastic boxes withmetal legs.

Project TimeA student at Dundee who optsfor this work will spend some300 hours of project timedesigning and making a chip tohis or her own specifications.The circuit has to be fairly

simple, of course, with fewerthan 150 transistors. We find thatMOSFETs with p -type channelsare simplest to make and weare usually content to turn outdevices with a separation of10 1./M between source anddrain. The layout details foreach chip are designed withthe aid of a mainframe com-puter and are stored on mag-netic tapes. Initial artwork isproduced from the tapes usingequipment for reproducingweather satellite photographs(we have not been fortunateenough to obtain the appro-priate pattern generator for thisstage). The main fabricationprocesses are then undertaken.To make working conditions asrealistic as possible, everyonewears a full set of cleanroomclothing resembling a surgicalhood and gown. Students arealso asked to assess the cost ofbringing each design to fru-ition.

This activity provides a wealthof practical experience andputs the importance of the lec-ture courses into perspective.Students are encouraged toconsult key research papers aswell as standard textbooks, tohelp them identify causes ofunexpected results or failuresthat arise from time to time inthe work. The aspiring inte-grated circuit engineer soonbegins to appreciate the im-portance of mastering the re-quired blend of electronicsengineering, solid state phys-ics, chemistry, crystallographyand metallurgy. backed -up bycomputer -aided design tech-niques.Almost 40 Honours studentshave now been introduced tointegrated circuit engineeringthrough the work of the micro-electronics laboratory. Post-graduate research and indus-trial contract work are sup-ported, too. Dundee graduatesin this field are now workingfor major manufacturingcompanies in the UK and over-seas, including GEC, Plessey,Ferranti, Hughes Microelec-tronics. National Semiconduc-tor, Motorola, British Telecom,INMOS, Mullard and Siemens.The chips our former studentshave been working on includethe Transputer and many otherdevices. Through this we gainuseful feedback about the con-tent of lecture courses and theareas that are interesting forresearch.Employers have been enthusi-astic about this practical ap-proach to microelectronics.When our graduates go to theirfirst job interviews carrying sili-con chips that they have madethemselves, their starting sal-aries have been good.

?.1W PRODUCTS NEW PRODUCTS TVA

Extensive rangeof phonesocketsAs part of its rapidly expandingservice supplying high -qualityJapanese components to theUK, Watts International an-nounces an extensive range ofphone sockets.The Emuden manufactured

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EE

July. August 198756

ATN FILMNET DECODERby J 8- R v Terborgh

Believe it or not, but a few days after our May issue was sent tothe printers, the engineers at ATN Filmnet altered the station's

scrambling system. The next thing that happened was SkyChannel abandoning encoding altogether for roughly a

fortnight.An article written for naught and circuits doomed to end up in

the junkbox? Here is the updata!

The speed at which dramaticchanges take place in the satel-lite TV world is very hard tokeep up with. After the publi-cation of '', we saw Europa TVdissappear and their 3WHtransponder temporarily as-signed to 3 -SAT. Music Boxchange into Super Channel,and ATN Filmnet adopt theMatsushita scrambling system,all on ECS-1. The launch of theDBS services for FederalGermany and France was post-poned for the umpteenth time,the flat dish was developed toaid in individual reception,Europe witnessed an invasionof relatively inexpensive LNBsof Far Eastern origin, and manyof our readers embarked onsetting up their own receptionsystem.Roundabout March 26 of thisyear, payTV channel ATNFilmnet selected scramblingmode 2 as a follow-up of mode1, which was analysed in 2., andhad been in operation sinceSeptember 1, 1986. Until thatmemorable day, it was not gen-erally known that theirMatsushita scrambling systemcan be programmed to provideseveral scrambling modes. It

has now evolved that sub-scribers' decoders incorporatea microprocessor -based systemthat selects and combines anumber of essentially simpledecoder blocks. This selectiongoes by wholly unnoticed to theregistered subscriber, and is ef-fected with the aid of a specialcode packet transmitted via thedigital subscriber's data chan-nel at 7.02 MHz in the baseband-see Fig. 1. It must reiteratedhere that the scrambling systemitself is not digital, and it isreadily seen that the power of

this multi -mode scramblingsystem resides in the possiblylarge number of available com-binations of methods, ratherthan in the complexity of eachindividual method. Therefore,now that mode 2 is operative,the use of the mode 1 decoderproposed in '2' is the same asusing no decoder at all, sincein both cases the picture iscompletely unintelligible. Andyet, the essence of the newlyadopted encoding method re-mains very simple, and is but anextension of mode 1, so that thedesign idea brought forward in

remains the basis for anyfurther designs.

New circuits for newmodes: 2 allThe circuit diagram in Fig. 2shows how the functionalblocks of Fig. 3 in '2 have beenworked out into a practicaldecoder. The 7.6 MHz FM re-ceiver for obtaining the com-

posite blanking signal is pur-posely shown as a separate unithere to make clear that it isalways required for decodingATN Filmnet, whatever scram-bling mode is, or will be,adopted (it may well be thatmode 3 or even 4 is operativewhen this article is being pub-lished...). The PLL and pulsetiming sections are largelyidentical to those used in theSky Channel decoder Z, so thata detailed description of theseis not required here.As already stated, mode 2 is anextended version of mode 1. Inaddition to shifting the DC com-ponent of the blanking, andinversion of the entire signal.the polarity of the video signalis now toggled for each raster inthe interlaced picture. This isvery simple to put right bydividing the 50 Hz blankingcomponent by two in bistableFF1, and alternately selectingthe DC -corrected VIDEO orVIDEO signal from the NE592differential amplifier on the

1

video

composite blanking

subscribers data

NBFM sound

main sound -T1

I !

5.0 6.5170 7.6I (MHz)

6.8ATN Filmnet baseband

87127 - 1

Fig. 1. Frequency assignment in the baseband transmitted byATN Filmnet.

vision/sound/PSU board in theElektor Electronics Indoor Unitfor Satellite TV Reception .

Provision has been made toensure that a viewable signal isalways available at the ACcoupled and CVBS-1 output.This is effected by rectifyingthe raster pulses in D.3 -C25 -R25and using the logic level so ob-tained to select between thedecoder output and the re-ceiver's CVBS-1 signal. LED D4lights when the signal from ATNis encoded. When it is notencoded, which is sometimesdone on purpose between filmsand during announcements offorthcoming programmes, thecarrier at 7.6 MHz is simply leftunmodulated.Since it was intended to keepthe decoder as simple as poss-ible, no provision has beenmade for automatically selec-ting the correct frame polarityof the video signal. This meansthat the SYNC button may have tobe pressed a few times toobtain a properly decoded pic-ture. The decoder remains syn-chronized when ATN switchesbetween encoded and non -encoded transmissions, butloses synchronization if thesignal strength at the receiverinput is too low, since spikesthen upset the operation of thefilters and the PLL Type 4046.

In practiceIt must be pointed out here thatthe decoder experiments dis-cussed require a certainamount of feeling for dealingwith RF and video signals. Also,the material presented here isessentially but a design idea,and the construction and align-

1131 EE

July/August 1987

2

e.6.12.62,

r0

rl

C2

L

%vim's. cis

0/ 40

0.001 10

E.C9.-.15514

Fri

f

.423

2 1521M. A2 C112.55

_141 = C5= 4.14355, ESC= ICE = tD14FFt= te 7 = 4313

I s

'1 CD -

Cr

5;2455 1111

I

Z54

MEMWIN

Ca, .25

12V

Fig. 2. Suggested design of an experimental mode 2 decoder for ATN Filmnet, the Dutch pay -TV channel on ECS-1.

ment of the circuits are given asa guide for advanced construc-tors and for experimental pur-poses only.Although ready-made inductorsare shown in the L1 and L3 -Lspositions, it is very well poss-ible to make your own fromavailable materials: this is likelyto ensure a rather higher Q fac-tor, and is certainly worth tryingwhen a grid dip meter is avail-able. Use an RF signal gener-ator to peak the top -coupledbandfilter and L4 at 7.6 MHz,and carefully tune Ls to that fre-quency by monitoring the out-put of the FM decoder with the

D -A converter forI/O busDecember 1986, p. 24.

In Fig. 3, the order of the databits Do -Drshould be reversed both at the bus con-nector and the inputs of ICI.

aid of a scope. Be sure to steerclear of the other signals in thebaseband. The operation andadjustment of the line blankingprocessor and pulse filtersneed no further detailing here,since this has been dealt with in2. The CBLANKING signal fromthe FM receiver is, of course,eminently suitable for trig-gering an oscilloscope whileanalysing further scramblingmethods from ATN's bag oftricks.

ConclusionAlthough the station controllers

Universal control forstepper motorsJanuary 1987, p. 46.

Table 5a should be amended as follows:M21 = 5Dh. In Table 5b, the databyte atM3E should read 00h.

at ATN Filmnet may changeto another of several more en-coding methods, this subject isconcluded here to concentrateon other matters to do with sat-ellite TV reception. As alreadystated, there is no way of know-ing whether the "mode 2" cir-cuit described here will be ofuse by the time this article isprinted, but enough technicalinformation should now beavailable to readily spot anychanges to the scramblingsystem, arid enable modifi-cation of the relevant circuitsections.

Bu:RGK

Literature references:Satellite TV Reception.

Elektor Electronics September1986.

'2 Decoding satellite TVsignals. Elektor ElectronicsMay 1987.

Indoor Unit for Satellite TVReception - 2. Elektor Elec-tronics November 1986.

EE

July/August 198758

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ElectrowipesfromElectrolubeUsed to clean, lubricate andprotect contacts and edge con-

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New telephoneconnectionboxes fromRendarRendar's range of telephone -network connector boxescaters for most internal inter-connection requirements.The range of five boxes in-cludes units which protectsensitive terminal equipmentagainst RFI and transients. BothA and B lines are protected,with advanced design filtering.

Further types provide sixseparate wire links from IDC(Insulation Displacement Con-nectors) to IDC, or from IDC toscrew terminals. Another boxallows IDC connection to stan-dard and non-standard cablediameters, and also to spadeterminals.Rendar LimitedDurban RoadSouth BerstedBOGNOR REGIS P022 9RLTelephone: (0243) 825811

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59 EEJuly/August 1987

OW PRODUCTS e NEW PRODUCTS NEVDigital timerA new and improved version oftheir popular Type ECT-1 timeris now available from Cobonicat £17.50 (excl. VAT). Apart fromclock and timer, the new ver-sion has a genuine stopwatchfunction and second intervals.The timer is eminently suitablefor commercial, domestic,educational, medical, or in-dustrial use. It is fitted with aspring -loaded clip for carryingon the person, and a magneticattachment. The clip can alsobe used for standing the timerupright on a table or desk. Itweighs only 40 g and measures60 x 60 x14 mm.The clock, which can be usedindependent of the timer, canbe used in the 12- or 24 -hourmode as required. The timingspan is from 1 second to23 hours 59 mins 59 secs. TheLC display is 8 mm high andshows hours, minutes, andseconds. A 60 -second alarmsignal is sounded when thetimer has completed its setcycle.Cobonic Limited32 Ludlow RoadGUILDFORD GU2 5NWTelephone: (0483) 505260

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Monitor testerhas widerange of signaloutputsNow available in the UK exclus-ively from Electronic Brokers is

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AutomaticFM/AMmodulationmeterElectronic Brokers has in-troduced the Marconi Instru-ments TF2304 FM/AM modu-lation meter which combinesbattery -portable operation withhigh accuracy, automatic tunigand automatic level setting.Designed primarily for the ser-vicing and production testing ofmobile radio communicationssystems, the TF2304 covers car-rier frequencies from 9-12 MHzand from 18-1000 MHz.

Iiiiiii1LI(' (5 (1 (4-..'---

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Thermal -arrayrecorderGould has developed a newthermal -array recorder whichincorporates advanced digitalwriting technology to providehigh recording performanceand flexible formatting ofresults - while maintaining

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EE

July/August 198760

pw PRODUCTS NEW PRODUCTS NEVPocket -sizedgas -poweredsoldering ironA powerful soldering iron thatcan be carried in a top pocket,Portasol is completely portableand is available from Freetrade(TEP) Ltd.No larger than a felt-tip pen andoffering a range of outputs from10 to 60 W, the Portasol is re-filled from cigarette lighterbutane gas containers. It issuitable for all types of pre-cision with a choice of tipdiameters - 1.0 mm, 2.4 mm,3.2 mm, or 4.8 mm. Maximumtip temperature is 400°C. Safeand reliable, it runs for approxi-mately one hour on a singlerefill. The clip -on cover has abuilt-in igniter and, when inposition, allows the Portasol tobe carried like a pen in a top -

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The T-1200SRscanningreceiverFieldtech Heathrow's newT-1200SR Scanning Receiver, theT-1200 is a microprocessor con-trolled, digitally synthesizedscanning receiver which fea-tures direct and remote elec-tronic signal analysis.The T-I200SR scanning receiverintegrates signal analysis func-tion of several instruments intoa signal compact and port-able unit which is capable ofmonitoring communicationsignals within the 100 kHz to999.9999 MHz frequency rangein 100 Hz steps.Fieldtech Heathrow LimitedHuntavia House420 Bath RoadLONGFORD UB7 OLLTelephone: 01-897 6446

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Datapulseannouncesnew switch-board trafficanalysis systemDatapulse has announced TAB,a new system which provides aseries of engineering reportson switchboard and exchangeline usage. The reports are de-signed such that they can bereadily understood by non-technical personnel who maybe responsible for a company'scommunications.

TAB is currently available forthe IDX family of switchboardsand examines data from the V24call logging port. The unit canoperate in two modes either asa line analyser or as a systemsanalyser. In the former, TABconverts binary records fromthe IDX port, turns them into aneasily recognisable format and,through the optional use ofnumerous selection parametersand flags, concentrates only onthat data which is relevant to theuser's current requirements.Datapulse LtdAubrey Watson House,Quebec RoadHENLEY-ON-THAMESRG9 1HATelephone: Henley (0491)571955 (3630-7F)

61 EEJuly/August 1987

EW PRODUCTS NEW PRODUCTS e NEV

Digitalmultimeter hasbuilt-in datacollectionfacilitiesElectronic Brokers has in-troduced the Philips PM2535digital multimeter designed forapplications involving data col-lection, reduction, and pro-cessing.The PM2535 utilises Philips'own advanced VLSI technologyto provide a resolution of 100 nVon a 300 mV measurement; ashort term stability of 0.002%;and a long term accuracyof 0.005%. To ensure totalmeasurement integrity at suchhigh resolution, the instrumentfeatures a true, fully guarded in-put which eliminates parasiticlead voltages and noise.Electronic Brokers Limited140-146 Camden StreetLONDON NW1 9PBTelephone: 01-267 7070

(3630-29F)

Microprocessor -controlledAM/FM signalgeneratorshave wide fre-quency rangeElectronic Brokers has in-troduced the Marconi Instru-

ments 2018A and 2019A AM/FMsynthesized signal generators,two new microprocessor -con-trolled instruments coveringthe frequency ranges 80 kHzto 520 MHz and 80 kHz to1040 MHz respectively.Microprocessor control pro -

The units are British designedand manufactured at thecompany's recently extendedfactory at Ryde, Isle of Wight.30 and 50 Watt units are avail-able in single, dual and tripleoutput versions. They are allMIL -spec products and are

gum - - lag 110 -

MUMB

3 11-1

S

ei

vides simple and rapid oper-ation by direct keyboard entryof settings and the non-volatilememory, which can store up to100 settings, further reducesmeasurement time.Electronic Brokers Limited140-146 Camden StreetLONDON NW1 9PBTelephone 01-267 7070

(3630-27F)

Pascall's ownrange ofmilitary/industrial PSU'sThe POWERMITE series is thefirst major new range to emergefrom Pascall's analogue ps.u. fa-cility.

I shielded to MIL -STD -461B forEMC/RFI. They are also en-vironmentally tested to militaryspecifications.Units in the range have aswitching frequency of 200 kHzand offer a maximum efficiencyof 85%. They operate from in-puts in the range +18 to+32VDC and produce a varietyof different outputs from 0.5 to10 A, depending on version.Single output versions providea +5, +24 or +28 V output; dualoutput units have +12 V or+15 V and triple output units of-fer +5 and +12 V or +15 V out-puts.Pascall Electronics LtdSaxon HouseDownsideSUNBURY-ON-THAMES TW166RYTelephone: 01-979 0123

(3630-26F)

New switchesfrom ITTCannonAimed directly at thetelecomms market, and otherapplications on PCBs wherespace is at a premium, are ITTCannon's new RTE /02 andRTE/03 switch styles.The switches are auto insert-able, flow solderable, and im-mersion cleanable, makingthem particularly suited to thelatest high volume assemblylines.

ITT CannonJays CloseViables EstateBASINGSTOKE RG22 4BWTelephone: (0256) 473171

(3630-18F)

EE

July/August 198762

BUILD THE ELEKTOR VALVE PREAMPWITH _ COMPONENTS

AND ENJOY SOUND QUALITY EVEN BETTER THAN THE ORIGINALIf you want the very best sound quality from an amplifier, you must use compo-nents of the highest quality. Standard 1% metal film resistors give a good perform-ance at a low price, but the Holco range of precision metal film resistors actuallysound so much better that AUDIOKITS sells hundreds each week to audioenthusiasts who are building new amplifiers or replacing the resistors in their exist-ing amplifier. At a typical price of 35 to 40 pence, can you really afford to use lowerperformance resistors? And for really high quality applications (such as the Elektorvalve preempt AUDIOKITS is selling more and more Bulk Foil resistors at prices ofE4.50 - E22 each.

January's Elektor gave an excellent summary on capacitors. AUDIOKITS suppliescapacitors of the very highest audio quality including IAR Wonder caps, close toler-ance polystyrenes up to 100nF and grade 1 long life electrolytics.

AUDIOKITS sells high quality semiconductors including MATO2FH lf81 andOP27GZ IE8.2.51 for use in the state of the art preamplifier; also OPSOFY (E14.001,OP77GP 160uV offset, E2.75). OP77EP 125.V offset, £6.501; also Boums conductiveplastic stereo pots, silver and gold plated switches, gold plated phono sockets,Kimber cable and much more.

To help you build the Elektor Valve Preamp or State of the Art preemie withAUDIOKITS components, AUDIOKITS are producing two technical notes whichinclude prices of components and advice on where to get better sound quality fromhigher quality parts. Price £2 each.

For full details of AUDIOKITS components and services, including some of the very'best complete amplifier kits available, please send 9" x 4" SAE to:

MOOOKOIre 7Eseri,2,001) Car1:116. Mill Close, Borrowash, Derby DE7 3GU, England

Tel. 0332 674929

en

NEW! fromJMMER 1987 ELECTRONIC

- CONS VICTORS CATALOGUE

e I. 66

C01040 II -/

/

(Bit se/A%Vett

/

MULTIMETERS

TO BE WON

1144,17,1/

PRICE ONLY k4 o Many new lines

Extended range£1 .20 of test equipment

£11 worth of discount voucherso 6 Multimeters to be won in easy to enter competition. Available at your local newsagent or direct from

address below.

access

(0992) 444111Cirkit Distribution Ltd Park Lane, Broxbourne, Herts ENID 7N0

Telephone: (0992) 444111 Telex: 22478

ULTRA HIFI CLASS APOWER AMPLIFIERS

The worlds most advanced active Class A MOSFET power amplifier, designed forlistening to, whilst engineered to break all performance limits_

* * * 50-150W 0/P, 4-16ohms, one unique module * * *THE 'SUPERMOS' There's no other amplifier module that can offer ANY

of these advanced features:

Integral heatsink, noedema] components needed.Sinpfy mounts onto a flatpanel, no awkward shapes)holes to cut.PSU requiernents 1_30 - 45V DC. fug detais with each anti:Rifler.Build the ultimate in class A sound quality at a fraction of the cost of twit units. SUPERMOSmodules E59 95 each total inc. SAE for dela&Coming soon, a true HiFi hybrid 24pin class A op -amp is the Superpre-amp

- Construction House, Whitley St,Bingley, Yorks. (0274) 568647

Active class A MOSFET 0/P (cool running)Distortion typically 0.0002% 12pprn)Slew rate greater than 250WpsHigh current capability of 50arrips p -pVery low feedback for superb sound qualityUnique gain stage for exceptional power supplyripple rejection.

sr

Ilifiler01to-D 0536 744664124 hr 7 days/week

747T1IS FIC

0) 20 25M 20 2501 20 2503 28 M18

2511 2314 20 2923 XI M21 20 M27 2742 4951 20 2574 20 39ES Mea 20 -6la so 55

132 49133 40 49139 40 49163 45 M

157 43 M158 Al 55161 -M 551E3 55 55164 % 551w 75

'88 e0 68FLOPPY

DISC CON-TROLLERS

.'.'OF ;400'0.01797 19001.1.-D3216 14267812 30760112 3075154 soaocceice 39)LA3T1 43158324 JOL1.12G7 120tAid.ia 5516US8 45

LAS3203 40 TL072 50OPOICP e. 11. 45111 18 TLCS4 45T1074 90 1100034 70

MEMORIESDRAM 5V IVMOS4154 E4541256 MSK 4418 18% .41484 64K

SRAM5V2114LP 1KMAP 2X

SRAM 5V611ELP 2% .ITISELP ix ,E LP MC rSE

EPROM 61/2776 2%27v 4K276I SK27123A TEX27256 321127512 812%

1 ED. M1 I:2291 CLEO1 £240

AIMOS4 E1_508 f2-50

CMOS8 El 308 £2408 C1450

HMOS8 E2708 12658 f2.458 02708 0.758 OUR

SAVE OVER NM ON OUREX EQUIPMENT MEMORIES

AND EPROMS, Me, e ,,,,,,,,,,,r5cuarb,ags

GUARANTEED UVERASED AND TESTED.411, 1 ex s EaTs

EPROMS2716 1( a C1.50

, 4K 8 E1232'--1-78:.... EK 8 E1534".. 16% 8 ELMAn taken from workingboards_ Tn. some_ You wit]SAVE POUNDS LOS

ADD VAT 15% ORDERS UNDER £25 ADD £1 P&P OVER 12.5 POSTAGE FREEORDERS DISPATCHED SAME DAY BEFORE 3.30 PM

DEPT lE7) 18 ROLDERNIEADOV,` A. CORBY NORTHANTS NNI8 9AI

Universal Semiconductor Devices Ltd.17 GRANVILLE COURT, GRANVILLE ROAD,

HORNSEY, LONDON N4 4EP, ENGLAND.

TEL. 01-348 9420/9425* TLX. 25157 usdco g

WE OFFER ONE OF THE LARGEST RANGES OF SEMICONDUCTORS AT 'Rata ECON-

OMICAL PRICES. THE FOLLOWING SEMICONDUCTOR TYPES ARE AVAIL-

ABLE FROM STOCK. IF WE DONT STOCK WHAT YOU NEED THEN WE CAN GET TTFAST FROM OUR FACILITIES IN WEST GERMANY AND USA UPON REQUEST.

TRANSISTORS -BIPOLARS - GERMANIUM AND SILICONSMALL SIGNALPOWER

DARLINGTONS - ALL SHAPES AND SIZESVHF. UHF DEVICES - ALL SHAPES AND SIZES

FETS - POWER MOSFETSUNIJUNCTIONS

DIODES - GERMANIUM AND SILICONRECTIFIERS AND BRIDGES

OPTO-ELECTRONIC DEVICES

LEDS OF ALL SHAPES AND SIZES

THYRISTORS AND TRIACS - ALL

-CrSHAPES

SIZES

INTEGRATED CIRCUITS RATINGS

CONSUMER - DIGITAL/ANALOGUEMICROPROCESSORS AND PERIPHERALS

IC SOCKETS

U.S.D. WILL

BE PLEASED

TO HELP

SUPPLY SEMI-

CONDUCTORS

FOR THE

SATELLITE TV

PROJECT

All semicon-

ductors For

system A amp

available on

special offer

JAPANESE COMPONENTS - VAST RANGE OF DISCRETES AND CONSUMER IC's.

MAIL ORDER CUSTOMERS PLEASE SEND FOR CUR COMPREHENSIVE PRICE UST

ENCLOSING £1-00 IN STAMPS, CHEQUE OR POSTAL ORDER

CATALOGUE SENT FREE OF CHARGE, WHEN REQUESTED ON OFRCIAL LETTERHEAD

(WITHOUT REFUND). TO OEM'S, SCHOOLS. COLLEGES, UNIVERSITIES. GOVERN-MENT INSTITUTIONS, COMPUTER FIRMS, ELECTRONIC REPAIR FIRMS AND DIS-TRIBUTORS.SPECIAL DISCOUNTS AND PAYMENT TERMS ARE AVAILABLE TO ABOVE INSTI-

TUTIONS.

PLEASE ENQUIRE FOR QUANTITY DISCOUNTS.WE WELCOME TELEPHONE AND TELEX ENQUIRIES!

EE

July/August 1987

ELMASET INSTRUMENT CASE300 133 217 MM deep El0 ea <£2.20>REGULATORSLM317T PLASTIC TO220 variable ElLM317 METAL £2.207812 METAL 12V 1A £17805/ 12/ 15/24v plastic 50p7905/ 12/ 15/24 plastic 50pCA3085 TO99 variable reg .. ElLM338 5A VARIABLE £5.00COMPUTER ICS27128-25 NEW £2.6027256-30 USED £2.502764-30 NEW 12.002732-45 USED £2.002716-45 USED E2.001702 EPROM EX EQPT £52114 EX EQPT 60p 4116 EX EQPT _ 70p6264-15 8k static ram £2.806116-2 ITC5517AP-21 £1.50SURFACE MOUNTED TRAN-SISTORSBCW30 BCW31 BCW72 NTAV70 2SA8121S2836 min 50/type 100/£2.50POWER TRANSISTORS2SC1520 sim BF259 3/11 100/122TIP141/2 Elea TIP112,125/428 2/E1T1P35B TIP35C £1.50SE9302 100V 10A DARL. SIM TIP121 21112N3055 EX EQPT TESTED 4/£1PLASTIC 3055 OR 2955 equiv 50p 100/£352N3773 NPN 25A 160V £1.80 10/116QUARTZ HALOGEN LAMPSA1/216 24V 150 WATTS E2.25HI 12V 50W (CAR SPOT) £1.50MISCELLANEOUSVN1OLM 60v 1/2A 5ohm TO -92 mosfet

4/11.00PCB with 2N2646 UNIJUNCTION with 12v4 POLE RELAY £1.00400MEG 0.5w thick film resistors(yes four hundred megohms) 41E1.00STRAIN GAUGES Foil type polyesterbacked balco grid alloy 40 OHMS £1.50 ea

10- /11.0012V RELAY 2 pole 6A contacts £1.25DIL REED RELAY 2 POLE n/oCONTACTS £1Zettler 24v 2p c/o relay 30 .20.12mm sim.RS 348-649 E1.50 100 t ElELECTRET MICROPHONE INSERT .. £0.90MODEM LINE TRANSFORMER . £1.50 1K

50pLinear Hall effect IC Micro Switch no 613 SS4sim RS 304-267 £2.50 100 -,- £1.50OSCILLOSCOPE PROBE SWITCHED X1X10 £10CHEAP PHONO PLUGS . 100/£2 1000/£181 pole 12 way rotary switch 41E1AUDIO ICS LM380 LM386 each ElCOAX PLUGS nice ones 4 El4 x 4 MEMBRANE KEYBOARD £1.5015.000pF 40V SPRAGUE 36D £2.50

<11.25>INDUCTOR 20pH 1.5A 5/£1NEW BT PLUG LEAD £1.501.25" PANEL FUSEHOLDERS 5/£1MAINS ROCKER SWITCHES SPST 6A 5/£1STAINLESS STEEL HINGES 14.5 x I"OPEN each £1TOK KEY SWITCH 2 POLE 3 KEYS ideal forcar/home alarms12v 1.2W small wire ended lamps fit AUDIVW TR7 SAAB VOLVO 10/El12V MES LAMPS 10i£1STEREO CASSETTE HEAD £2MONO CASS.HEAD El ERASE HEAD 50pTHERMAL CUT OUTS 50 77 85 120°C El eaTHERMAL FUSE 121°C 240V 15A___.5/£1TRANSISTOR MOUNTING PADSTO -5/T0-18 13/1000TO.3 TRANSISTOR COVERS 10/£1STICK ON CABINET FEET 30/£1PCB PINS FIT 0.1" VERO 200/£1TO -220 micas bushes 10/50p 100/MTO -3 micas bushes 20/£1kynar wire wrapping wire 2oz/E1PTFE min screened cable 10m1E1

Large heat shrink sleeving pack £2CERAMIC FILTERS 6M/9M/10.7M .... 50p

100."£20TOKIN MAINS RFI FILTER 250v 15A E3IEC chassis plug rfi filter 10A £3Potentiometers short spindlesvalues 2k5 10k 25k lm lin 5 £1

500k lin 500k log 4. El40Khz ULTRASONIC TRANSDUCERS EX-EQPT NO DATA El /prPLESSEY INVERTER TRANSFORMER 11.5-0-11.5V to 240v 200VA- £6 (E2)LARGE QTY AVAILABLE100W STUD ZENER DIODES . 11.50 ea.10/11/12'16.24.30/33/43/62/68'82 volts

DIODES AND RECTIFIERS1N4148 100/11.501N4004/SD4 IA 300V 100/131N5401 3A 100V 10/£1BA157 IA 400V fast recovery ... 100/M.50BA159 lA 1000V fast recovery 100'£4120V 35A STUD 65p12FR40 12A 400V small stud 4/11.50BY127 1200V 1.2A 10/11BY254 800V 3A 8:£18Y255 1300V 3A 6.111A 800V BRIDGE RECTIFIER 4,£14A 100V BRIDGE 3 'El6A 100V BRIDGE 2 , E110A 200V BRIDGE £1.5025A 200V BRIDGE £2 10/11825A 400V BRIDGE £2.50 10/£22

SCRS2P4M equiv C106D 3/El 100/120.00MCR72-6 10A 600V SCR £135A 600V STUD SCR E2TICV106D 800mA 400V SCR 3/El 100 115MEU21 PROG. UNIJUNCTION 3 El

TRIACSTRIAC 8A 400V TO220 5/£2 100:£30.00TXAL225 8A 400V 5MA GATE 2 '£1

100/£35ACOV8FGM 800mA 400V TO92 TRIAC 3: ElDIACS 4/El

CONNECTORSCENTRONICS 36 WAY IDC PLUG... £3.50CENTRONICS .36 WAY IDC SKT £4.00CENTRONICS 36 WAY PLUG SOLDERTYPE E4USED Centronics 36 way plug socket E3USED D CONNECTORS price per pairD9 El, 015 E1.50, D25 £2. D37 £2,050 £3.50 covers 50p ea.

WIRE WOUND RESISTORSW21 or sim 2.5W 10 of one value . ElR10. R15, R22, 2R0, 2R7, 389. 4R7. 5R0.5R6, 8R2, 10R, 12R. 15R. 18R. 20R, 22R,27R. 33R, 36R. 478. 56R, 62R, 91R, 100R,120R, 180R. 220R. 390R. 430R. 470R, 560R,680R, 8208. 1K2, 1K5, 1K8, 2K7. 3K0, 3K3,5KO, 10K_R05 (50 milli -ohm) 1% 3w 4 for El

W22 or sim 6W - 7 of one value El822. 847. R62, 882. 1RO, 1R5, 1R8. 383.6R8, 9R1, 10R, 12R. 20R, 24R, 27R, 33R.478, 518. 56R. 62R, 1008. 120R, 180R, 2208.390R, 560R, 6208. 910R, 1K0. 1K2, 1K8, 212.2K7, 3K3. 3K9. 4K7. 8K2. 10K, 16K, 20K.

W23 or sim 9W -- 6 of one value ElR22, R47, IRO, 1R1, 3R0, 158. 56R, 62R.120R. 180R. 2208, WO. 1K5, 5K1, 10K.

W24 or sim 12W -- 4 of one value El850. IRO, 2R0. 6R8, 981, 10R. 22R, 47R,68R, 75R, 82R. 100R, 150R. 180R, 200R,220R, 270R, 400R. 620R. WO, 10K. 15K.

PHOTO DEVICESSLOTTED OPTO-SWITCH OPCOAOPB815 £1.302N5777 50pTIL81 PHOTO TRANSISTOR £1TIL38 INFRA RED LED 5 ElOP12252 OPTO ISOLATOR 50pPHOTO DIODE 50p 6/12MEL12 (PHOTO DARLINGTON BASEn; c) 50pRPY58A LDR 50p ORP12 LDR 70pLEDs RED 3 or 5mm 12/£1 100/16LEDs GREEN OR YELLOW 10/11 100/16.50FLASHING RED LED 5mm 50p 100,120

SUB MIN PRESETS HORIZONTAL15 El 100 E5

1K 4K7 10K 22K 47K 1M 10N1

MULTI TURN PRESETS 3/4"IOR 208 1008 2008 5008 2K 5K 10K 22K 50K100K 200K

SOLID STATE RELAYS NEW10A 250VZero voltage switching Control voltage8-28v dc 12.5040A 250V AC £18

POLYESTER/POLYCARB CAPSini3n3/5116,13n2/ion 1% 63v 10mm 100. 1610n i 15n/22n /33n/47n /68n10mm red 100/13.50100n 250v radial 10mm 100/£3100n 600v sprague axial 10/11 100/16 1£112A2 160v rad 22m 100/£1010n/33n/47n 250v ac x rated 15mm 10/E1470n 250v ac x rated red 4/£11U 600V MIXED DIELECTRIC 50p ea

MONOLITHIC CERAMICCAPACITORS100n 50v 3mm or 5mm .... 100/16 lk '£40100n ax short leads 1001£310n 50v dil package 0.3" rad £4'100

£35.1000100n 50v dil package 0.3" rad El0r 180

IC SOCKETS6 pin 15/118 pin 12/El

14/16 pin 10/£118/20 pin 7/£1.22/24/28 pin 4,E140 pin 30p

STEPPER MOTORS 4 PHASE 2 9VWINDINGS E3.50 10 £30

TRIMMER CAPACITORSsmall all types 5/60pGREY 1.5 to 6.5 pFgrey larger type 2 to 25 pFpurple 3pF to 50pF

BEAD THERMISTORSGLASS BEAD NTC Res at 20'c E1.00250R. 1/C2. 50K, 220K. 1M4

PLEASE NOTE CHANGE OF ADDRESS - SHOP IN ILFORD NOW CLOSED

KEYTRONICSP.O. BOX 634, BISHOPS STORTFORD,

HERTS. CM23 2RX.Telephone 0279 505543

MIN ORDER E2.50 OFFICIAL ORDERS WELCOMEUNIVERSITIES COLLEGES SCHOOLS GOVT DEPARTMENTS

P&P AS SHOWN IN BRACKETS (HEAVY ITEMS)65p OTHERWISE (LIGHT ITEMS)

ADD 15% VAT TO TOTALMAIL ORDER ONLY

ELECTRONIC COMPONENTS BOUGHT FOR CASH

EVEN MORE SUPERSUMMER SAVERS!!If you are already a Maplin customer, soon you will be receiving (if youhaven't already) a [umber bundle of smashing Summertime specials.plus the chance to win a beautiful, sleek. Ford XR3i (if you register in theprize draw before 1st July 1987).

If you are not a Maplin customer, but would love to know more about thespecial offers and have a chance to win the car, fill in the coupon belowwith your personal details. tick the appropriate box, and post it now.

The ApacheA superb ready -built scale -model off -road racer complete with a2 -CHANNEL DIGITAL PROPORTIONAL RADIO CONTROL SYSTEM- for the price of the RC system alone!All this is included in the price:Ready -built scale model car (overall size 325 x 186 x 130mm, 12.8x 7.3 x 5.1in.).Front and rear low -profile semi -pneumatic rubber tyres.Front wheel independent suspension.High or low gear selection.Sealed box with differential gearing.Powerful motor gives scale speeds up to 140 mph.Front and rear coil -spring shock absorbers.2 -channel digitaloroportional radio control transmitter (and receiver).(Standard 27MHz AM - no licence required in UK).Servo -controlled proportional steering.Proportional motor speed control in forward and reverse.

'Batteries and -cad charger not included. Car requires 8 AA cells (ru-cadIri nirecommended YGOOA El 35 each)_ Transmitter requires 6 AA cells. (alka-line SX69A 55p each or ni-cad as above). NB- and if you have a collision at100mph or more. you'll be pleased to hear that spare parts are available.

I'LL BE RACING THIS SUMMER WITH fillY supEno APACHE CAR!Pl42sr, rush me my Apache model racer. with 2 channel digital proportional radiocontrol system I wish to receive:

Code thy Price

Apache model racer SX08J

AA ni-cad battery YGOOA

AA alkaline battery SX69A

Al 1 prices include VAT. Please add Sep towards postage. Total- - -- - - - -- ' - - - - -I enclose cheque postal order made payable to Maplin Electronic Supplies Ltd . orsee credit card detailsHere are my personal details:

Customer Number

Name

Address

Q IPost Code

Send to:Maplin Electronic Supplies Ltd.P.O. Box 3, Rayleigh. Essex, SS6 SLR. Telephone. Credit Card Sales (0702) 554161 Enquiries (0702) 552911

!have zeen a Map!si Custc:- :: I would be p'eacto rece.:e :=tails of the super me special offers

It you have already received the Summertime special offers.please use the Order Coupon suppled with that

Please register me in the prize draw

jTick box.

nTick box.

I authorise you to deter my Credit Card account for the cost of goods despatched.

Credit Card Number H I 1 I 1

Access American Express Me card VisaDelete as required

Note: (-1-inric will be despatched only if the address given is the cardholders addressIt ordering by Credit Card please sign.

Signature Expiry DateE 7/8 87

&wigs 41 Lyr4On Square. Pe/1'y Ban. Bernrignam Tel 021-356 7292 159-161 KIng SUft1 HaffirnerVreh London W6 Ye} 01-748 0926 8 Oxford Rd ManchesTer Tel 061-236 028146-48 13erces Va6ey Saultiampten Tel 07'33 25831 282-284 Lonoar$ Ra.. Wesr_141-unsea Tel 0702-554000