No.8 - Spring 1982 Please circula te

The Quarterly for BBC Engineering StaH

In this edition of ENG 'NF

ENHANCED ON AIR Page I

EDITORIAL Page 2

TRANSMITIERS OPENING AND CLOSING Page 2

ELECTRONIC STILLS STORE Page 3

TV WAVEFORM ANALYSER Page 4

NEWSTUDIOS FOR BH Page 4

AUTOMATIC TESTING The BBC has made the first public Blue (RGB) samples, occupying some Page 5 broadcast of high quality still pictures 1.2 M bytes of storage space. This by means of the UK Telctext system. represents an active picture size of 702 EXTENDED PAL The broadcast high-quality pictures and by 576 pixels, or picture elements, to Page 5, 6, 7 . other enhancements were demonstrated fIll the television screen with the high- to a technical committee of the quality picture. For the experimental DIGITAL TRANSCODER European Broadcasting Union (EBU) on transmission, a montage of the startling Page 8 February lIth, and at a meeting of the pictures of Saturn taken from the Institution of Electrical Engineers (lEE) Voyager 2 spacecraft was used to NCl RE-ENTERS SERVICE on March 8th. The UK teletext system demonstrate the capability of the Page 9 has, for many years now, represented an system. The picture was fed from a efficient and rugged way of trans- conventional 35 mm slide scanner into 4000 VPR 2'S mitting, receiving and decoding data for the digital picture store. After sampling Page 10 display on a television receiver. None of at 13.5 MHz it was fed to a the efficiency or ruggedness is lost in microcomputer and data generator that RADIO MAINTENANCE the transmission of the enhancements. sorted the information into a form Page 10 The recent transmissions were the suitable for transmission. The special culmination of several years work by equipment was used temporarily to TRANSPORT DEPT. COMPUTER engineers from Special Projects Section replace two of the conventional four Page 11 at Research Department. The line Ceefax signals on BBC 2 for the equipment used to generate the transmission. STEERABLE ARRAY enhancements contained a teletext The Voyager 2 picture was Page 11 generator. a microcomputer system and included in a series of pages that a high-quality digital picture store. displayed an improved character font. SILVER STREAK LICENSED whose content was displayed on a The new character generator in the Page 12 screen. On the UK television standard decoding equipment enabled the (System 1) the store opcrates at thc characters to be more easily read, with AWARD TO ENGINEERS CCIR recommended sampling rate of individual characters being weJI spaced Page 12 13.5 MJ-Iz. with 8-bit Red, Green and 'continued on Page 3' 'ENG INF' Spring 1982 - Page 1 Editorial The recent announcement that the BBC is to be allowed to operate two satellite channels has been welcomed. Thus the BBC enters another era of broadcasting. As technology has improved, so have the services which the BBC has been able to offer its audience. None of these improvements would have been possible without the dedication and skill of BBC engineers. For many years now BBC engineers have been investigating the problems to be found in the 12 GHz band, and seeking solutions. Some of the problems have been answered, others await international agreement. Fifty years ago the BBC entered a new era when it moved its headquarters from Savoy Place to . At that time the Press were quick to blame the BBC's high-power medium-wave transmitters for the series of wet summers that had been The following 405 line transmitters experienced. With the advent of are expected to close as shown: satellites, how long before the Press 1983 make this accusation about satellite BBC Transmitters - First Quarter broadcasting? Bath (Avon) Congratulations Weymouth (Dorset) Mr. Peter Rainger, Deputy Direct- Manningtree (Essex) or of Engineering, has been elected Wensleydale (N. Yorkshire) a Fellow of the Royal Society for Richmond (N. Yorkshire) Weardale (Co. Durham) contributions to electronic techniques Llangollen (Clwyd) used in television. Our warmest Newry (Co. Down) congratulations to him. Frank Be"isford, Assistant Head Wenvoe Channel I3 (South Glamorgan) Welcome of Engineering Information We welcome Keith Hunter from IBA Transmitters -First Quarter Department, retired on 1st March after Bath (Avon) VT in Cardiff to our team of 25 years' service. Ridge Hill (Hereford) contributors. Keith has kindly agreed . After serving in the Royal Navy S1. Hilary Channel 10 (South Glamorgan) to supply Eng Inf with cartoons, and an BBC Transmitters Second Quarter example of his excellent work is from 1940 till 1946 and in Government - Bamstaple (N. Devon) published elsewhere on this page. We Communications until 1956, Frank joined the BBC as an Engineer in Thrumster (Caithness) look forward to seeing some more of his Orkney cartoons in the future. Broadcasting House. He moved to External Services in 1958 and became a Bressay (Shetland) Alan Lafferty Senior Maintenance Engineer at the Grantown (Badenoch & Strathspey) Caversham monitoring station three Kingussie (Badenoch & Strathspey) Transmitters years later. Ammanford (Dyfed) Opened Frank is probably best known for Kilvey Hill (Swansea) his work in E.I.D. which he joined in Llanidloes (powys) The following uhf tv relay stations have 1964. His wide knowledge and IBA Transmitters -Second Quarter opened since January: enthusiasm ensured that the public, the Huntshaw Cross (N. Devon) Ipstones Edge, Staffordshire retail trade, and the radio and television Rumster Forest (Caithness) Romaldkirk, Co. Durham industry were all reliably informed Aviemore (Badenoch & Strathspey) Weaverthorpe, North Yorkshire about BBC engineering developments, BBC Transmitters -Third Quarter Wivenhoe Park, Essex particularly those affecting transmission Douglas (Isle of Man) Newry South, Co. Down or reception. There can be few Ballater (Kincardine & Deeside) Llanharan, Mid Glamorgan representatives of the industry that have Toward (Argyll) St. Anthony-in-Roseland, Cornwall not heard his witty explanations of BBC Lochgilphead (Argyll) . Bretch Hill, Oxon policy from some platform or other. Rosneath (Dumbarton) West Wycombe, Buckinghamshire Since he became A.H.E.I.D. three Millburn Muir (Dumbarton) Coleford, Gloucestershire years ago Frank has represented the IBA Transmitters -Third Quarter Pinwherry, Strathclyde BBC in many negotiations with the Richmond Hill (Isle of Man) Ballantrae, Strathclyde Home Office on frequency planning and Whitehaven (Cumbria) Vhf Radio policy matters. Rothesay (Argyll) Wrotham -now mixed polarisation Phil Laven, the BBC's Senior Rosneath (Dumbarton) Local Radio Engineer in New York for the last three BBC Transmitters -Fourth Quarter Radio Guernsey - Rohais (mf only) years, takes over as the new Assistant Lame (Co. Antrim) Radio Jersey -Trinity (mf only) Head. Whitby (N. Yorkshire) Page 2 - 'ENG INF' Spring 1982 "ENHANCED CEEFAX" Electronic Stills Store Evaluated 'continued from Page l' An experimental prototype of an the new digital coding standard. The in the words. electronic store for still pictures was main signal storage is provided by one Another innovation that was constructed for studio operation to of the latest 8" Winchester magnetic broadcast was "linked pages". In the enable pictures originated in electronic disc drives which is completely sealed. present Ceefax system there are often form to be stored and selected for trans- Two digital semiconductor picture pages where the content has some mission at the studio. stores are used as buffer stores. relevance to another page in the The need for such a stills store Operation of the equipment is magazine. Viewers wishing to retrieve was identified some time ago. controlled by a Z80.based the additional pages need to re-select Traditionally, artwork and captions, microprocessor which also provides the page number and wait for the etc., have been photographed and slides picture processing for grabbing moving magazine to cycle round until they produced, and these have been pictures. receive them. Using "linked pages" the broadcast using a studio slide scanner. Initial tests with the prototype Ceefax Editor would decide which pages More recently, however, direct studio store were most encouraging and were associated with each other, and electronic methods have become showed that such a system could be would add extra information to link available for originating many of these readily incorporated into existing them together. In the enhanced signals. Extensive use is. now made 0f studios. Throughout last December and decoder the pages would be stored and electronic character generators and the January, the prototype studio store was instantly displayed when the relevant BBC Broadcast Computer is also used in installed in the apparatus room of TC7 . linked page number was selected. For the generation of electronic pictures. It was established that the unit could example, the news index on page 201 With the advent of new electronic provide an extremely valuable general on BBC 2 could be linked to graphic drawing systems like 'Flair', it studio facility. Studio cameras were background information, news head- has become important that studios are used to enable still pictures of general lines, and complete news stories which provided with an all-electronic studio activities or artwork to be stored. the viewer could retrieve at the touch of equivalent of the slide scanner. It was also found to be beneficial to a button without waiting for the The prototype studio store store signals from the slide scanner so magazine to cycle round. provides storage for 40 pictures. These that the slide scanner mechanism was For some time now the Ceefax can be selected for transmission either not required to change slides 'on air'. In Unit have been transmitting teletext randomly, using a number keyboard, or the course of these tests, a brief software in conjunction with Brighton in sequence using a single "CUT' demonstration recording was made Polytechnic and several schools to see if button. 'MAIN' and 'PREVIEW' showing how a weather map could be it is possible to transmit computer outputs are available so that, where crudely animated by moving the programs by means of Ceefax, which sufficient monitoring facilities exist, the weather symbols between successive could be directly loaded into a micro- next picture can be previewed while a pictures and replaying the pictures at computer memory. With the advent of picture is 'on air'. Signals input to the three second intervals. the BBC Microcomputer, and using the store can be previewed before being Further developments of the teletext adaptor that will become recorded. Input and record operations studio store are now in hand. It is available later this year, it will be overwrite previously stored information intended to construct a second possible to use the Ceefax service as a and are two button operations. The experimental prototype incorporating source of software for the computer control keyboard contains numeric improvements and suggestions made system. It has been shown that using displays of the numbers of the pictures during tests with the first. It is also prototype equipment it is possible to being output and can be operated hoped to develop a method of download programs into the BBCMicro- remotely from the main equipment. conveying pictures between stores using computer, without the need to copy the Signals are input and output in a removable cartridge. Eventually a program and then re-enter it via the analogue RGB form and are processed design may be made for quantity computer keyboard. As well as being and stored in digital YUV form using production. able to download teletext software, the teletext option associated with the BBC Microcomputer will also respond to the "linked pages" which are now being transmitted. Most of the enhancements to the Ceefax system require additional memory in the receiver decoder, and it is not likely that the full range of enhancements will become available until later in the decade. All of the enhancements are compatible with existing decoders. For example, viewers selecting the pages carrying the picture information will currently receive the text without decoding the picture information. The characters are displayed in the existing format. When the enhancements are transmitted as part of the service it is likely that the ~ editor will nIl in the gaps where the Adriiln Durey, Research Department, operates the control keyboard of the picture would have been by a simple prototype studio store. A new picture has just been accessed and is being output graphic so that the viewer is not left via the preview output. The main output is displayed on the right-hand monitor. with a blank screen.

'ENG INF' Spring 1982 - Page3 TV Waveform Analyser Engineering Designs Department have recently completed the . Cl development of the automatic TV wave- --- form analyser (ME3/S02). The design is seen as a replacement for several - separate items of existing test equipment including automatic ITS monitoring equipment which is at present in service at transmitter stations.

Both traditional analogue and NUAl, AUTO modern microcomputer techniques have been blended to produce an instrument with sufficient flexibility to accommodate new measurement allows a selection of different measure- of internally stored limits. There are 32 requirements by changing micro- ments to be made in sequence using fully independent sets of lin1its stored computer software. either ITS or full field test waveforms. within the microcomputer memory, The new equipment is able to If the BBC test waveform generator, each set consisting of upper and lower make precision measurements on either type GE4M/S61, is used to provide the red, and upper and lower amber for full field test signals or the insertion test test signals then the analyser is able to each of the 30 measurement parameters. signal carried during the field blanking identify the particular test waveform This is provided to give in a single interval, and has the capability of and set itself so as to make the instrument the capability of providing providing up to thirty independent appropriate measurement. Intelligent monitoring at any position in the whole requirements. The measurements operation can be further enhanced if a of the BBC distribution network. include amplitude, noise, linear and control line is available from the Full remote control is possible non-linear waveform distortions, inter- analyser back to the GE4M/S61 with the analyser and a BCD output of modulation interference and transmitter waveform generator. Under these the readings is provided for logging modulation depth. conditions the analyser can remotely purposes or telemetry. The analyser can be used either in control the generator to produce the The analyser is mounted in a 4U a manual or automatic mode. The waveform necessary for any given high bay width chassis and will be manual mode enables an operator to measurement. available in both portable and rack make measurements of a single The results of any measurement mounting forms. parameter, whereas the automatic mode are continuously compared against a set Broadcasting House: New Studios ACED contractors have as three new News and Current Affair Broadcast Systems Unit A are to completed the demolition work at the studios, with 'Mixer' Studio 3B being provide studio control panels which will rear of BH and are now halfway rebuilt at the same time. This new interface with the new microprocessor- through the construction of a 2-floor studio, together with the new 3K, 4C controlled solid-state source selection extension above the roof of the Concert and SA Studios, will be equipped with system. This system will feature plain Hall gallery. It will be the first addition the general purpose range of control language entry, and display sources by to BH since 'The Extension' was built. desks. means of a keyboard and alphanumeric This work is part of an SCPD-led project Desks from all three suppliers of LED displays. Unit A will also be to provide new facilities for News and general purpose desks, Audix, Calrec installing a Pye M100 intercom system Current Affairs. and Neve, will be included in the to replace the existing News Production Work first began in February development. Calrec have been awarded intercom. The old system is an Ericsson 1981 when a fiffi1 of specialist a contract for a 32-channel, 3 group 14 crossbar type, which is already contractors demolished the old boiler- outside source Mark 3A desk for 3B as overloaded. house chimney using a 2 foot diameter, well as for the Technical Operator's News and Current Affairs studios hydraulically-driven, diamond-tipped position that goes with these desks. tend by their nature to have a profusion circular saw. Bearing in mind that the Studio 4C will also have a Technical of intercoms, telephones, picture chimney consists of one foot thick very Operator's position: Neve will provide a monitors, printers and other peripheral pebbly concrete with reinforcing rods Mark 4, 24-channel desk in Studio SA, equipment. With the growing every six inches in both directions, which will be a discussion studio. importance of Ceefax and vidiprint, lateral and vertical, the process was Audix will supply a 12-channel Mark 4A these and other data communications remarkably quiet. Although Studio 3B for Studio 3K. This desk is capable of systems are under consideration for the and the Concert Hall were put out of one-man operation and will act as a new area. As the areas are all fairly action, the disturbance to the rest of the back-up studio/recording area to Studio compact care has to be taken when new building was minimal. 3B. A smaller back-up area for Studio equipment is brought into the studios. The main building contract began 4D will be equipped with a Glen Sound For this reason extra planning meetings in June, with the demolition of the rear GSNT.l console. The general purpose have been set up between ACED, wall of BH itself. This was to allow for desk Mark 3, 3A and 4A are and the News and Current Affairs, the the addition of the new steel-framed developments from the basic general user department, to try and integrate as structure. The extra space within this purpose design. They are the result of much of the extra equipment as possible structure will house a replacement News close co-operation between Radio 0 & into the interior design of the new Intake Recording area and some offices. M's Technical Consultative Committee The first of the new studios will This will make building available for use and SCPD's Radio Studio Unit. SCPD's be in service early in 1983. Page 4 - 'ENG INF' Spring 1982 EXTENDED PAL CODING for SATELLITES

The quality of present-day The present-day VI< 5.5 MHz video In a wider-bandwid th satellite or television pictures is limited by the transmission bandwid th is adequate for optical fibre channel there is room to available transmission bandwidth and by 625-line monochrome pictures. The transmit the filtered-off high frequency the capabilities of currently available limitations become apparent when the luminance components separately. The display tubes. There is no very colour signals must be squeezed in with high frequencies (3.5 MHz upwards) are immediate sign of any large bright higher the monochrome. Ingenious though the shifted in frequency to a higher band definition display device to take over PAL coding system may be, it is (8 MHz upwards) and transmitted from the shadow mask Cathode Ray impossible to avoid some mutual together with the original low frequencies tube, but many workers are in the field interference between monochrome and chrominance signals. The upper limit and we can expect some development (luminance) and colour components. of the separated high frequencies could during the next few years. These interferences show themselves as extend above the 5.5 MHz equivalent Assuming, then, that a better luminance appearing in chrominance bandwidth of the present transmission display becomes available what channels (cross colour) giving rise to channel. possibilities are there for wider flashes of false colour on striped suits for A new receiver, specially designed bandwidth transmissions to match? Both example; and chrominance signals for this wide bandwidth transmission Satellite Broadcasting and optical fibre appearing in the luminance channel give system, would shift the transmitted high cable distribution offer wider bandwidth spurious dot patterns. To reduce these frequencies back to their original values and Research Department has been effects to acceptable levels, signals in the (3.5 MHz upwards) and hence display a considering how these could best be region of the colour sub-carrier much-enhanced degree of fine picture exploited. A key factor in any new (4.43 MHz) are attenuated, usually detail. The new receiver would of course transmission system must be resulting in loss of all signal frequencies also be free from cross colour effects, compatibility, whereby existing receivers from about 4 MHz up to the 5.5 MHz since the high frequencies would be could continue to work with band limit. So the majority of colour re-inserted after colour decoding had new-standard signals, although new receivers roll-off about 4 MHz and show taken place. receivers would be necessary to derive full little fine detail whilst still suffering from Research Department have benefit. For at least the early years of some degree of cross colour aberrations. demonstrated experimental coders and satellite or optical fibre cable services it A new proposal involves decoders working on this principle and would be required that existing receivers fIltering-off high frequency components has passed extended bandwidth signals, continue to be usable, with appropriate above 3.5 MHz. This gives a very slight with associated digital sound channels, converters. The introduction of any non- reduction in picture defiriTtion, scarcely through an RF link simulating a satellite compatible system could require many noticeable on present-day display-tubes, channel. Results were very satisfactory years for international agreement and but virtually removes all possibility of and showed also that the proposed new receiver development and hence interference between luminance and system is entirely compatible with seriously delay the establishment of chrominance components so that cross continuing use of present-day receivers. satellite broadcasting in this country. colour effects disappear. "PHOTOGRAPHIC EXAMPLES" Page 6 and 7 EQUIPMENT DEPARTMENT:Automatic Testing

The Equipment Department Test The General Purpose Interface set the oscillator to the channels in Laboratory is now using automatic Bus (GPIB), the generally used name for Band 4 and 5, and a modulation methods to test a range of audio the system, has 16 lines, eight for data, analyser made four different types of amplifiers, power supplies and and eight for interface communication measurement on each channel. oscillators, using equipment based on a management. Three of these More recently the same basic general purpose interface connection management lines are used for system has been used for testing audio system. "handshaking" a technique which amplifiers. The desk top micro- For some years the use of co-ordinates the transfer of non- computer controls an audio test set to automatic testing has been closely synchronous data. A microcomputer originate measure signals, a digital watched, but available systems were acts as Controller, and this commands multimeter to measure resistance and generally specialised and intended for and receives data from the other instru- d.c. volts and current. A switching high-volume production. Some ten or ments on the bus. Each instrument has matrix configures the test set up for so years ago Hewlett Packard developed its own address and can either be a each test. Measurements are made of a standard interface bus system which "talker", a "listenp,r", or both (talkers various circuit resistances, gain, allows test instruments to communicate provide information to the bus, listeners frequency response, noise, distortion and exchange data with each other receive information). etc. The cost of writing the program under the control of a stored test The system was first used in was saved on the first batch of program. This system was adopted as Equipment Department to test amplifiers tested. American standard, IEEE-488, and later synthesised oscillators for the "Silver At the present time a permanent as International Standard IEC-625. Streak" UHF transposer, where it was automatic test system for power However, it was not until the low cost required to make a large number of suppliers is being assembled. The microprocessor came on the scene that a measurements to ensure the unit was techniques will be adopted for an wide range of data-controlled operating correctly. A desk top increasing range of units as the system is instruments were produced and made microcomputer (HP85) controlled a developed, resulting in lower costs for the system attractive. device to originate logic signals which equipment made in Avenue House.

'ENG INF' Spring 1982 - Page 5 CONVENTIONAL PAL

The uncoded picture Test Card F direct from the slide scanner without any form of PAL coding.

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Test Card F via Conventional PAL coder and decoder The spurious patterns on the diagonal bars at the corners of , the picture and on the resolution gratings to the right of the clown are caused by crosscolour - the PAL decoder wrongly interprets fine detail in the picture as colour information because both are transmitted in the same frequency band. The next-to-bottom resolution grating is removed by the notch filter in the decoder.

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Page 6 - 'ENC INF' Spring 1982 EXTENDED pAL

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Extended PAL - Test Card F as seen with a conventional PAL decoder Current television receivers are not capable of displaying the full resolution of pictures transmitted by the PAL system. This is because of bandwidth restrictions in the receiver's circuitry and I I --1 lack of resolution in present-day display tubes. But current receivers do reproduce the spurious coloured patterns known as crosscolour caused by the colour decoder wrongly interpreting fine I I L detail in the picture as colour information. Thus the owners of current receivers would lose little if the fine detail which cause H: .; J. r .,1 crosscolour is removed; in fact they would gain because " crosscolour would be eliminated. This photograph of a Test Card taken from a high-quality picture monitor shows both the reduction of crosscolour and the loss of fine detail; but tests have shown that on a domestic receiver the paramount effect is the , reduction of crosscolour.

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I Test Card F via Extended PAL coder and decoder " In the Extended PAL system the fine detail is transmitted in a separate frequency band from the colour information. Thus there can be no crosstalk between the two signals; there are therefore no spurious patterns on the diagonal bars at the corners of the picture or on the resolution bars to the right of the clown. Furthermore no notch mter is needed in the Extended PAL decoder. Thus the fidelity of the picture is maintained up to the highest resolution.

'ENG INF' Spring 1982 - Page 7 DIGITAL TRANSCODER

In February, Designs Department data streams, which each occur at data streams at 6.75 M word/s and delivered a second digital transcoder 6.75 M words per second are converted back to analogue signals in (C06/511) to Television Network multiplexed together to make an 8-bit two digital to analogue converters Department. It joins an identical parallel 'chrominance' data stream at (DACs). These signals are then equipment, which has been in service 13.5 M word/so The chrominance and connected to an analogue PAL coder since November 1981, alongside the two the 13.5 M word/s luminance stream are together with the luminance signal from ACE digital standards converters in the each fed to a pair of identical picture a third DAC. This coder, which is fed Standards Conversion Area at Television stores. Each store consists of eight 4-V with local pulses, provides the Centre. circuit boards and each board carries transcoder's output. Much technical development has thirty-two 16 kbit random access Operation as a PAL-to-P AL Synchron- taken place in the three years since the memory (RAM) chips with associated iser ACE design was completed. There is input and output registers. These As well as SECAM, the equipment now an EBV coding standard for digital boards are essentially the same as those can accept analogue Y, V and V signals television and these new transcoders are used in the ACE standards converter from an external PAL decoder, or the first equipment using this standard except that the older ACE boards use digital luminance and chrominance. A to go into service. The standard is based 4 kbit RAMs. PAL detecting circuit can cause either on line-locked sampling frequencies of The 13.5 MHz and 6.75 MHz line- of these inputs to be selected 13.5 MHz and 6.75 MHz for luminance locked clock signals 0 f the ADCS are au tomatically. This enables the and colour difference signals generated from syncs separated from equipmen t to be used as a PAL synchro- respectively. the decoded input luminance signal. niser for re timing or 'repairing' out-of- Problems of SECAM-PAL Transcoding The RAM addresses into which the data specification PAL signals. It is, of The digital transcoders will is written are also derived from these course, important that the PAL decoder replace two fifteen-year-old analogue input syncs, so that a particular address removes all traces of the original equipments, which were also made in always contains the information for the chrominance from its luminance output Designs Department. Both the new and same part 0 f the same line of the input and to this end, it is planned that a the old machines have a SECAM picture. comb-filter decoder of the type used in decoder connected to a PAL coder, but The data output from the store is the ACE converters will be used. in the new transcoders the connection is controlled by clocks and addresses [n the transcoder's design, great via a digital picture-store synchroniser which are derived from local mixed care was taken to make it as tolerant as and the output is fully synchronous syncs. The store's reading and writing possible of defective input signals. The with local pulses. processes are therefore asynchronous so clock pulse generator has a 'Time Base This removes a major difficulty that it operates as a synchroniser. Correction' mode of operation in which which existed with analogue The luminance and chrominance it follows the sync timing jitter on transcoders. The line-frequency data from the store are blanked digitally signals from helical-scan recorders. tolerance of the SECAM standard by comparing the data with 300 ns Isolated, grossly mistimed link sync (:t 0.02%) is much wider than for PAL rise time sine-squared edges stored in pulses are ignored and a previously (:t 0.001%). If a transcoder produces a read-only memories. The field blanking stored line is substituted. Non-sync cuts PAL output with the same line component can be either standard width and misplaced field syncs cause a frequency as the SECAM input, it is or narrowed to allow insertion signals in previously stored field to be used. [f impossible to maintain the specified the blanking interval to pass through the the input signal fails altogether the relationship between the PAL line and transcoder. transcoder output is maintained with a sub-carrier frequencies without The blanked chrominance data is black-level signal until the input signal exceeding the PAL sub-carrier demultiplexed into separate (V) and (V) 'continued on Page 9' frequency tolerance. If the sub-carrier frequency tolerance is exceeded, PAL decoders may be unable to lock to the burst - and if the line-to-su b-carrier frequency relationship is not maintain- ed, VTRs cannot handle the signal. To cope with this difficulty the analogue transcoders had two outputs: one with the correct sub-carrier frequency, for transmission; and another with the correct sub-carrier-to-line frequency relationship, for recording. Signal Processing The new transcoders use a commercial SECAM decoder modified to give luminance (Y) and colour difference (V) and (V) output signals. These analogue outputs are turned into eight-bit parallel digital data by three analogue to digital converters (ADCs), each of which uses a TRW high speed The digital transcoder is handed over to Network Department. The photograph 'flash' converter integrated circuit TDC shows (left to right) Ralph Barrett (Network), Mike Turner (SCPD) and Roger 1007 J. The two colour-difference Robinson (Designs Department).

Page 8 - 'ENG INF' Spring 1982 NETWORK CONTROL for [fJ[fJ{fJ symbol, and the School's Clock which D originate from Designs Department The new BBC I Network Control Operational Assistant (POA) from the equipment. This has superseded Room (NCI) and continuity suite have Control Room. Transmission facilities "", the ageing camera-originated recently entered service at Television such as VT or TK machines, studios and symbols system. A camera is still used Centre. Network Control is the last Outside Broadcasts can be routed by the though, to generate the "rotating point of control before the network POA to the presentation mixer in the world" symbol seen at programme programmes reach the transmitter. A Control Room. Under the control of junctions. Design of a solid-state device small staff of five (Network Director, the Network Director the VT and TK to replace it continues. Assistant Senior Television Engineer, machines can be remotely started, and Two BAIO/501 slide scanners and Presentation Operational Assistant, the relevant programme sent to the an Autocue opacity machine are used to Network Assistant and Announcer) are transmitters at the correct time. The generate caption cards, such as those responsible for the minute by minute presentation mixer is a 24 channel seen at programme junctions to trail operation of the network at anyone video/audio Grass Valley 1600-48, with both network 1 and 2 programmes. A time. full automatic or manual control plus Network Assistant selects the slides, and In the Central Apparatus Room video key and sound-over facilities. checks that the correct ones are (CAR) there is a 100 source by 120 NC1 incorporates the latest solid- available to the Network Director. destination switching matrix which is state picture sources, such as the At one end of the control desk controlled by the Presentation network clock, the Open University the Assistant Senior Television Engineers (A S Tel E) has facilities for checking the technical quality of the incoming and outgoing signals. Besides the usual vectorscope and oscilloscope he has full communications and talkback facilities, LS 5/8 monitor speaker, and colour monitor. 0 ff-air signals from Crystal Palace are also available so that the network output can be compared with the transmitter output. A bank of 23 black and white, and 3 colour monitors enable the Network Director to check the quality of output, preview programmes, and check slides and captions. Also housed in the Network Control Room is "Presfax" which makes use of "ICE" the Insertion Communications Equipment. Inserted The refurbished NC1 Control Room at Television Centre. on line 21 of the television waveform of the digitally-coded signal allows the Control Room to send messages to "DIGITAL TRANSCODER" displayed together with the normal regional centres telling them of changes 'continued from Page 8' input signal in a split-field presentation. to the schedule times or linking reappears and two good fields have been Having a known good reference signal announcements. The data is displayed stored. enables the alignment of the decoders on a screen in a similar format to that Remote Control and coder to be checked. used for Ceefax. ICE also features in The transcoders, like the ACE To help locate any faults in the Outside Broadcast applications; for equipments, are remotely operated from store, another test facility is provided example, when the satellite ground CAR. which puts vertical 'Store Test Cursor' station is used in remote locations it is The controls available include a lines on the output picture. These lines often difficult for British Telecom to function called 'Data-Reverse' which are one clock-pulse wide and, by adjust- provide telephone control lines. On reverses the order of significance of the ing thumb-wheel switches so that a such occasions the OB team carry an bits through most of the digital process- cursor line corresponds to the position ICE decoder, enabling CAR to ing. This facility is provided so that of a fault in the picture, a particular communicate with the OB. should a fault occur which affects a location in the store can be identified. Adjacent to the Network Control highly significant bit, the visual effect Other switches enable the faulty bit to Room is the Continuity Announcers' can be made less noticeable by moving be identified and, by combining this room. Equipped with a Cox video and the fault to a less significant bit. information with the cursor position, audio 'knob a channel' manual mixer, Test and Maintenance Facilities the precise RAM chip at fault can be the Duty Announcer controls the One benefit of digital systems is identified. presentation junctions. He can also the way in which equipment can be A microprocessor-based monitor- control simple programme junctions and reconfigured and test signals generated. ing system is under development. This has limited access to the automatic The transcoder, for instance, will monitor two transcoders and report mixer system in the Main Control incorpo rates a digital test-signal the mode of operation of each in text Room. The Continuity Announcer also generator, the output of which can on picture monitors in CAR. It will also has control of sound sources such as replace the normal input to the store. A give warnings if the equipment temp- grams, cartridge machines and tape variety of colour bar signals can be erature or any supply voltages depart recorders, as well as the microphone generated and, if required, these can be from normal. used for linking announcements.

'ENG INF' Spring 1982 - Page 9 AMPEX make RADIO MAINTENANCE 4000 Tape recorders The 4000th recorder of the Ampex helical-scan VPR-2 series has been delivered to Television Centre. The recorder, a studio console VPR-2B complete with TBC-2B digital time base corrector, is part of an order for 8 machines. With this, the 4000th VPR-2, the number of Ampex VPR-family recorders supplied to the BBC totals 67. A further seven recorders (VPR-2B and VPR-20) are to be delivered on current contracts. Commenting on the "4000" mile- stone, Gerhard Wick, general manager of Ampex (Europe, Africa, Middle East) said: "Last year, 1981, marked the Eric Palmer and Dave Austwick maintain equipment in the new maintenance test room twenty-fifth anniversary of the in Broadcasting House. invention by Ampex of the first ment and augmented by a further four practical recorder for broadcast Changes in the organisation of the maintenance services for Radio in to provide a team of six Handyman television. Then, the technology was Cleaners who provide all-round support quadruplex. Increasingly now on the London were introduced towards the end of last year with a view to for the engineering staff. world-wide scene the technology is The Senior Engineers with the becoming the one-inch helical-scan improving the engineering support available to those using the programme areas for which they are responsible are: system, in which once again Ampex has Sen. Eng. News & Network Maintenance been a pioneer. To have brought 4000 making facilities in B.H. and the adjacent buildings. The technical areas - S.D. Hatherly VPR-2 series machines to the market in Sen. Eng. Basement Studios only four years on top of many have been divided into four groups and independent maintenance teams have M.O'Shaughessy hundreds of the earlier VPR-l series is Sen. Eng. Upper Studios an achievement unparalleled by any been set up, one for each group. Three of the groups have been provided with P. Guest other manufacturer. Sen. Eng. Outside Studios "We are especially pleased", new Test Rooms and the fourth occupies the old Shift Maintenance D.C. Homer added Mr. Wick, "that this four- The organisation and method of thousandth recorder is entering service Workshop, which will be fully refurbish- ed in the near future. Each of the operation has been based on the with the BBC, which has been a valued experimental unit set up 3 years ago at customer, and invariably a demanding groups is headed by a Senior Engineer Maida Vale under Sen. Eng. Alan one, for many Ampex products for who is charged not only with the main- Stokes. more than twenty years". tenance of the broadcasting plant, but Speaking on behalf of the BBC, also has responsibility for ensuring that Initial indications are that lines of communication have been shortened George Cook, ADE, said: ''We in the all technical areas are kept clean and and the programme makers are very BBC would like to congratulate Ampex tidy with the decor and furnishings maintained in good order. Two pleased with the new more personalised on achieving their 4000th VPR-2. This service. machine and its one-inch and two-inch technical cleaner posts were transferred predecessors have been of fundamental from C.S.G. to the Tech. S.R. establish-

importance in the development of tele- tracking', the patent Ampex AST vision production techniques, and it system. comes as no surprise that the The VPR-2B is an advanced broadcasters' demand has reached so version of the VPR-2 which offers a significant a level. reverse slow-motion capability together "It is a pleasing coincidence that with other new features and the 4000th VPR-2 has come the BBC's improvements. The latest option for way and we are appreciative of the close the VPR-2B allows true-frame playback attention which Ampex has always in stop-motion. The true-frame option given to us. I am glad we are regarded essentially doubles the vertical as a 'demanding customer' and no doubt resolution in stop-motion and offers we shall continue to earn this dramatic picture improvements in some description and so maintain a fruitful instances. Ampex/BBC relationship". 'c' format tape recorders, like the The Ampex helical-scan VPR VPR2, are gradually replacing worn out series was launched in 1976, and has quadraplex machines, some of which George Cook, ADE (right), accepts the subsequently been developed to meet have been service since 1959. The 4000th VPR2B video tape recorder to the most demanding requirements of introduction of the new machines be manufactured by Ampex, from broadcasting and television production allows significant savings in tape storage Gerhard Wick, General Manager companies, particularly by the space and costs. (Europe, Africa and Middle East). introduction of 'automatic scan Page 10 - 'ENG INF' Spring 1982 Transport Department TRAMS Steerable Array at It may come as something of a In essence, this allows the BBC's surprise to learn that the BBC operates central vehicle ftIes to be stored on a more than 1,200 vehiclesup and down computer. The contents of a whole row CAVERSHAM the country. Some are light vans and of ftIing cabinets have effectively been estate cars for news teams, cameras condensed to a series of electronic A new type of receiving aerial and the like, but a large number are pulses. system is now in operation at commercial vehicles, with as wide a It's not really quite as simple as Caversham. The system was designed range of body types as you're ever likely that though, as Ralph Lewis, the and constructed by engineers Henry to find in a single fleet, -anythingfrom Assistant Transport Manager, says: Price (now with External Services), and simple box vans to the highly complex "There are still a lot of bits of paper Adrian Robinson at Research CMCCR2. that have to be put somewhere." These Department. The aerial array forms a Looking after such a varied fleet is include purchase and licensing narrow beam which can be steered not made any easier by the fact that the documents, for instance, for which the electronically to any direction. It thus vehicles are spread over about 100 original ftIes are maintained. For ea~h has the ability to select the wanted different locations around the country, vehicle, a comprehensive array of signal from the many interfering and/or some with fully-equipped garage information, such as make, model, jamming signals coming from other facilities, but others just remote registration number, body type, gross bearings. The array operates in the h.f. outposts such as transmitting stations, and unladen weights, supplier and broadcast bands over the frequency where only one or two vehicles may be replacement cost, along with a lot of range 6 MHz to 26 MHz. based. other details, can be stored in uniform If conventional aerials are used, Management of the whole fleet is fashion and displayed in consolidated either a large collection of fixed co-ordinated by Equipment Department form on the v.d.u. screen or printed out. directional aerials is needed, in order to at a central office in Weir Road. The The vehicles are designated by make, cover all the points of the compass, or functions of Transport Department are model, registration number and chassis alternatively a mechanically directional to buy and sell the vehicles, tax and number; no fleet numbers are used. The aerial must be used. Such arrangements maintain them - and make sure that the computer can also list vehicles by model occupy a lot of space or are unwieldy to user departments are paying a designation or by chassis number, or operate. reasonable price for running costs. any other parameter desired. The new array is compact and That may sound simple. But it In practical terms, one of the first easy to use, and has an additional demands constant vigilance by the ways this facility has helped Transport feature to suppress particularly difficult department's staff - for instance, to Department in drawing up consolidated jamming signals more effectively. It make sure that vehicles they never see lists of vehicles needing taxing, and comprises eight 2m vertical elements in are correctly taxed. and regularly MOTs each month. a line at 5m spacing, and a bay of aerial- maintained. It also demands a perpetual The next facility to come into use signal combining equipment. The key flow of information between staff and was 'User Charging Report' which to such a simple array is the use of a the numerous vehicle locations, and an provides Management Accountant with high input-impedance, high-quality rJ. almost continual updating of records. the rates to be charged on vehicles amplifier at the base of each element. It sounds an ideal situation for operated by user departments. This The signals from the elements are then some kind of computerised control; report identifies the quarterly standing passed to variable delay lines housed in and that's what Transport Department charge and the mileage charge for each the bay, and combined to feed the thought too. vehicle. monitoring receiver. Following discussions with several A unique feature of the system is The array is arranged to form a firms, Transport Department called in its ability to provide 5-year and I-year beam which is steered by adjusting the A. J. Associates of Beckenham, Kent, a replacement plans. These reports lengths of the delay lines. The small consultancy and software house. identify vehicles to be replaced, the date necessary calculations are done by a Besides being ready and willing to draw at which they will achieve their planned micro-processor which is at the heart of up a computer programme to suit their life and the required budget provision. the control system. At the request of needs, A. J. Associates had close links What of the cost of all this? the Monitoring Service, a serial data link with Wang, a computer manufacturer Ralph Lewis puts it at around £15,000- has been provided, so that the array can. whose range included a medium-sized, which, as he says, is "not much more be controlled remotely, in the same way self-contained system that looked ideal than the price of some new Bedfords" as the associated receiver. for the job. (of which the BBC has many). In any An additional feature, not In hardware terms, what the case, the cost is modest when you available with conventional aerials, is Transport Department has acquired consider the savings and improved the ability to steer a null against looks remarkably straightforward and management control that have resulted. particular interfering signals. Initial compact. The Wang 2200-series reports from the Monitoring Service computer itself is not much bigger than (Condensed from an article in "Bedford have been encouraging. For example, a desk-top copier; it contains a Operator"). using the steerable array, it is possible to Winchester memory disk with a capacity receive a usable signal from Teheran of 4 megabytes, and has the facility for Radio whilst it is not resolvable with the small 1 megabyte "floppy disks" to be other aerials available at Caversham. inserted. In terms of software - A. J. This intercept was particularly useful in Associates came up with something *** providing valuable news reports at the called TRAMS, short for Transport time of the assassination of President Management System. Sadat.

'ENG INF' Spring 1982 - Page 11 'transposed' to another channel without NICAM AWAl~D the signal being demodulated and then reprocessed. Because it is intended for use in small buildings, often on isolated sites, the transposer has been designed so that no adjustments at all are required on site. This is done by using, for the first time, universal modules in which all active components are similar. A separate panel, known as the 'personality' panel, which contains no active units determines the frequency, offset, slope, maximum gain and output power by providing control to the transposer's active module. II' a fault does develop, as soon as the replacement module is plugged into its associated 'personality' panel it is auto- matically set to the required character- istics. The 'personality' panel, consist- ing of two uhf bandpass filters and a simple control circuit should outlast the Engineers from Designs Department received the Lord Mountbatten Premium .life of the transposer. (1980) from the /ERE for a paper published 0/1N/CAM 3. The photograph shows The modular construction allows /ERE Acting President, Professor William Corling (second from right) presenting the equipment to be very flexible in the the award to (left to right) Alan English, John O'Clarey and Robin Cable. The way it can be arranged for single or Lord Mountbatten Premium is awarded annually for the most outstanding paper multi-channel operation. Normally in on the engineering aspects of electronics or radio. the it has four separate modules for the BBC 1, BBC 2, IBA and the fourth channel allocation. Replace- ment modules allow for quick and easy SILVER STREAK LICENSED main tenance. Each service has its own transposer module and in turn each Bryce McCrirrick, DE, and David The 'Silver Streak' was initially Young, Managing Director of developed by Designs Department to module has three detachable units - a Continental Microwave Limited of provide full broadcast quality television power amplifier, an IF amplifier with Dunstable, Bedfordshire, met recently equipment at minimum cost but with mixers and a dual frequency synthesiser. to sign a licence agreement for maximum reliability for the BBC's As already explained there are no Continental Microwave to manufacture programme for relay stations serving in tegral con trois. and market the BBC-designed 'Silver areas of small population. A transposer The equipment has been Streak' Uhf Transposer equipment. allows a signal, received from a master designed for high reliability at an (See Eng 1nl' No. 3) station on one channel, to be economic price by using fewer more generously rated components and by keeping the operating temperature low. The signal path through the distribution amplifier is duplicated so that any single transistor failure will only result in a loss of gain rather than a loss of service. Although the duplicate signal path is not continued through each module because of the cost, several stages do have a parallel configuration to improve both performance and reliability. This winter has provided an excellent reliability test for the first transposer, which was installed at the Braemar television relay station. Temperatures of below -20 degrees Celsius were recorded and the equipment went on working satis- factorily. As the equipment was designed to allow modification, it is expected that transposers will become available for vhf television and for international standards other than System I.

DE signs the licence agreement with David Yol/Ilg of Continental Microwave Limited. * * *

Page 12 - 'ENC /NF' Spring 1982 Published by BBC Engineering Information Department, and printed by Print Unit, ETD, Wood Norton