No. 10 - Autumn 1982 Please Circulate

The Quarterly For BBC Engineering Staff

BBC helps Rank Cintel In this edition of ENG INf

BBC AND RANK CINTEL Page 1

THE MERRIMAN REPORT Page 2 Q I TRANSMITTERS OPENED \I I Page 2

EDITORIAL Page 2

INTERNATIONAL CONVENTION 1982 Page 3

AUTOMATIC REVERBERATION TIMER Page 4

VIDEO ROSTRUM CAMERA Page 4 View of the prototype line-array telecine. HEADPHONE LlMITER On the eve of the International cameras, domestic television Page 5 Broadcasting Convention in Brighton cameras based on their use are now came the announcement of two obtainable. However, it was recognised FIBRE OPTIC TRANSMISSIONS important agreements between the BBC from the outset that they could find an Page 6 and Rank Cintel. The first was the earlier application in the televising of result of a collaborative agreement for fIlms. This is because the motion of the LS 5/9 LOUDSPEAKER Research Department to conduct film as it runs through the telecine can Page 6 research into improvements into fIlm be used to provide one of the two transmission techniques as applied to television scans; thus a simpler solid- TYPE 5 CMCR telecine machines. This has resulted in state sensor, consisting only 0 f a single Page 7 some novel features that will be Hne of around 1000 picture elements can be used, as compared with a two- incorporated into Rank Cintel STEREO TV SOUND machines. The second agreement allows dimensional array of nearer 0.5 million Page 7 for the manufacture under licence of elements which would be required for the studio stills store (described in Eng television camera applications. ELECTRONIC F Inf No. 8) and now to be marketed Although the flying-spot scanning Page 8 under the name of "Slide File". method using a CRT and photo- Line-Array Telecine multipliers is preferred for post- Engineers at Kingswood Warren production work, the latest line-array have been conducting research into the sensors are capable of producing broad- use of solid.state image sensors in cast quality pictures and offer several broadcasting since the end of 1972. advantages over camera-type and flying- Although solid-state sensors have still spot systems: not found a place in broadcast-quaHty 'continued on Page 8' 'ENG INF' Autumn 1982 - Page 1 Editorial Merriman The reputation and standing of the BBC engineers has, once again, been Report enhanced by their contributions at the Earlier this year in June, the recent International. Broadcasting Home Secretary, in a written Parlia- Convention. Hardly any delegate or mentary reply, set up an independent visitor could fail to be impressed by the review of the radio frequency spectrum high standard of technical papers or from 30-960 MHz. quality of engineering exhibits. This As part of the review he charged hard won reputation should be guarded the Chairman, Dr. J .H.H. Merriman CB, closely, and not allowed to slip. The OBE, F.Eng. and his committee, introduction of cable television, and Air Vice Marshal, A. Foden CB, CBE additional satellite channels in the and P.M. Vine, Esq., CBE, DL, to make . L..c.\1i'wE., (,.\-1(.., Q,f\'r1'E::,(t.,'1._' not too distant future will undoubted- a recommendation with some urgency fC-a::'fAG\.., .._ \ ly provide a challenge to the BBC. by September 1982 on the future IBC always produces its lighter usage of tv Bands I and Ill. moments amongst the serious discuss- The Committee recently reported ions. Somecne suggested that the back to the Home Secretary, and the Transmitters 1/20th scale model of L-Sat, being used substance of their recommendations to demonstrate our involvement in DBS, were that;- Opened be made to rotate; the air-draught thus (i) Continuing, even acceler- caused could be used to cool the ating, demand for spectrum space The following uhf relay stations exhibits (and staff) down. Congrat- requires the maximum exploitation of have opened since July: ulations must be extended to Don emerging alternative technologies Polperro, Cornwall Kershaw for winning, of all things, a wherever practicable and major changes Aislaby, North Yorkshire VHS recorder in a competition on the to current usage. Ogbourne St. George, Wiltshire Ampex stand! (ii) Bands I and Ill, with their Hart/and, Devon Stereo Sound particular propagation and coverage Mevagissey, Cornwall For some time both viewers and qualities, should increasingly provide Bossiney, Cornwall industry alike have been asking when the main radio frequency spectrum Swimbridge, Devon the BBC would start stereo sound trans- areas of exploitation for a combination Boscast/e, Cornwall missions with television (see elsewhere of mobile services and services in Over Norton, Oxon in this edition). It must be emphasized operational support of broadcasting, Holmfield, West Yorkshire that the experiments now taking place with priority when necessary for mobile Hang/eton, East Sussex are just that. There is absolutely no services. Rye, East Sussex guarantee that this system, or any other, (iii) Britain's television broadcast- Wootton Courtenay, Somerset will be adopted by the BBC. Everyone ing services (whether for picture or text) Micklefield, Bucks will just have to be patient and await are likely to be best served to the end of Orton, Cumbria the outcome of the Research Depart- the Century by maximum exploitation Afon Dyfi, Powys ment experiments. of, and earlier concentration of Thurso, Highland Engineering Ties resources upon, the emerging combin- Banff, Grampian ations of uhf, satellite and cable For those engineers who are . Strathblane, Central interested, Designs Department have services. Ness of Lewis, West Isles (Highland) just produced a "BBC Engineering" tie. In implementing this strategy, Dumfries South, Dumfries & Galloway They are available in or maroon, they recommended:- Largs, Strathclyde and feature the BBC logo, engineering (iv) 405 line tv services be Vhf lion logo, and the word "engineering" closed by the end of 1984; Exeter, St. Thomas, Devon woven onto the background. They cost (v) a revised mobile radio £2.75, and can be obtained by writing frequency allocation plan be developed to me at 701 Hemy Wood House, in consultation with manufacturers and stating colour preference. The next users by the end of 1983; ... batch will take about six weeks to (vi) a revised broadcast ancillary manufacture and deliver. services radio frequency allocation plan Alan Lafferty be developed in consultation with communication links, had been recog- Broadcasting Authorities by the end of nised. The lack of available ancillary 1983, service frequencies could seriously In responding to the report, the affect the cover given to important BBC regretted the recommendation that national events. ENG INF 1983 television broadcasting should be with- The recommendation for earlier The final dates for sending stories drawn from Band I and III for all time. than planned closure of Band I and III for inclusion in Eng Inf are as shown. Although there is no identifiable stations will mean a loss of service to Engineers with information should demand for broadcasting in these Bands, viewers in remote areas who are still contact Alan Lafferty on LBH 5432 or pressure could develop for local or area dependent upon vhf signals. Many of Room 701 HWH. broadcasting that could only be accom- these viewers will eventually be able to Spring -March 4th modated in these Bands. receive uhf signals off air from newly Summer -June 3rd However, the BBC was pleased to constructed relay stations. However, Autumn -September 2nd note that the importance of broadcast- there will be some time when they will Winter -November 25th ing ancillary, services such as OB be deprived of a service entirely.

Page 2 - 'ENC INF' Autumn 1982 INTERNATIONAL IBC BROACCASTING B2 CONVENTION BRIGHTON 18-21 September 1982

on the seafront was used to demonstrate an automatic reverberation timer developed by Research Department. Many of the equipments featured by Designs Department on the exhibition stand were available for licence by British manufacturers. The ME3/502 TV waveform analyser (see Eng Inf No. 8) was coupled to a digital fibre-optic link, and visitors were able to test both exhibits simultaneously. The 2kW Band II amplifier, recently licensed to Eddystone Radio Ltd., dominated one corner of the exhibition, and The crowded BBC stand created much interest. Also of interest were the generation of electronic graphics used, for example, as the open- ing sequence for TV News, or the Open University rotating symbol. Elsewhere the potential of "Editrace", the two machine video tape editing equipment was demonstrated. A practical demon- stration of headphone limiting equip- ment allowed visitors to hear for them- selveshow the equipment worked. Engineering Training Department creat~d considerable interest in their colour TV training package, with many enquiries from visitors from the UK and abroad.. BBC engineers played an and Designs Departments. On the promenade SCPD were important part in the 9th International Details of the exhibits are given demonstrating the last of the Type 5 Broadcasting Convention (IBC) held, elsewhere in Eng Inf, but are sum- CMCRs to be manufactured. Television once again, in Brighton from September marised here. OBs demonstrated the potential of their 18th to 21st. Seventeen papers, From Research Department came mobile satellite ground station; the covering technical subjects from solid- a demonstration of high-quality text design has just been licensed to state sensors to satellite broadcasting, used to demonstrate improvements in Marconi and will now be made available were read by engineers from specialist alpha-numeric fonts. The studio stills to other broadcasters. Radio OBs and operational departments. Review- store, recently licenced for manufacture demonstrated one of their two mobile ing the impact of new broadcasting by Rank Cintel Ltd., and borrowed studios. Inside the control room were a technology on future broadcast services, from Television Centre for the pair of the new LS 5/9 monitor loud- Charlie Sandbank (HRD) spoke at some exhibition, was used to demonstrate speakers for visitors to appraise. length on Direct Broadcasting by how live pictures could be "grabbed" An estimated 1200 visitors a day Satellite (DBS), , the and stored; these included some start- came to the BBC stand in the exhibition role of the microprocessor in broadcast- ling pictures from the Type 5CMCR on hall; (where the air-conditioning still left ing, and high definition television. the seafront! Many visitors were a lot to be desired). No single exhibit Some of the new technology attracted to the demonstration of captured the show, but the hard work mentioned in HRD's paper was on Extended PAL which was freely avail- of many engineers made each exhibit display in the accompanying exhibition. able for discussion with the specialist valuable in its own right. Twelve exhibits from Research, Designs engineers on the stand. A prototype Credit must be given to all of the and Engineering Training Departments adaptor for the BBC micro- staff who worked hard over many provided a lively demonstration inside computer allowed visitors the chance to months to make IBC worthwhile. the crowded exhibition halls. Outside see Telesoftware in action. Thanks must go to Research, Designs, on the promenade three OB vehicles Using signals specially radiated Studio Capital Projects, Television VT, created much interest to both con- from the Rowridge vhf transmitter, Engineering Training, Radio OBs, ference delegates and general public research engineers demonstrated the full Television OBs, Equipment and alike. Space inside the exhibition halls potential of "Radio-data", the Engineering Information Departments being at a premium, one vehicle from experimental system used for station who each contributed to the overall Radio OBs, also contained some inter- identification and programme labelling. success of the exhibition and con- esting new technology from Research The studio part of the Radio OB vehicle ference. 'ENG INF' Autumn 1982 - Page 3 Automatic Reverberation Timer Better Rostru A new video rostrum camera and a digital picture storage system have .. been developed to overcome many of the difficulties encountered when using conventional fIlm rostrum cameras in a ...... television environment. A video tape recording, demonstrating. the new . . system, was shown on the stand at ,,-.. mc. The video rostrum camera ..... The new video rostrum camera comprises a television camera with a 15: 1 zoom lens moun ted on a column over a horizontal table top. The camera and lens are counterbalanced and are free to travel up and down the column. The BBC carries out acoustic full-scale time axes from 0.5 s to 15 s. Artwork is placed on the table top measurements as part of the acceptance The displayed dynamic ranges of both which can be rotated and moved along procedure on almost all new or the individual and average decays are the north/south and east/west axes. refurbished areas in which sound quality 60dB, the gain of the microphone Also set into the table top are four is important. These areas include all amplifier being automatically adjusted sliding tracks (called 'panning bars') types of studios, control rooms, listen- over the range 40 to 100 dB to start the designed to accurately locate and move ing rooms and recording areas. In display of the decays near to the top of separate pieces of artwork individually. addition to the acoustic background the displayed range. Reverberation All these table functions are computer noise level and the sound insulation to times can be measured accurately over controlled, as are the zoom, focus, iris adjacent areas, a measurement is also the range 0.1 s to 15 s, with less and level on the camera and lens. made of the average reverberation time accurate estimates down to 0.06 sand The video rostrum camera is as a function of frequency. Using con- up to 60 s. The instrument is capable of operated from a control desk which ventional methods, this last measure- being operated remotely as part of a comprises two panels and a visual ment is extremely laborious and time larger integrated acoustics measuring display unit. The operator can program consuming, requiring a manual analysis system via an integral interface bus, a sequence of table positions and of about four hundred and eighty which is designed to the IEEE - 488 camera operations into the control individual recordings of the decay of GPIB standard. system. These can then be automatic- sound energy as a function of time. Although designed specifically for ally replayed whilst the result is viewed With the sixty to one hundred areas measuring times the instrument may be on a picture monitor. Movement may which need to be measured in the BBC used for any other types of measure- be slowed down or stopped at any time each year, use of this manual method ment which require a signal source with to check the effects being generated. would require a large amount of effort. 1/3 octave wide bandpass fIlter and a Any necessary changes can easily be An automated, microprocessor- receiving chain. The receiving chain made to the control data before the controlled, measuring system for reverb- consists of an optional variable gain final output is recorded. eration time has therefore been microphone amplifier, rectifier and log- The programmed route can be developed. It employs the same basic arithmic analogue-to-digital converter. traversed in a continuous motion or can measurement procedure as the earlier In addition the individual elements of be stepped along frame by frame. manual method but uses a micro- the instrument were designed to be This stepped movement is especially computer to control the individual easily used for other purposes. For useful for cell animation where it may elements and to record the decay of example, the display controller can be be necessary to change the artwork for the sound energy. A clear, annotated used as a high resolution (256 x 256 every frame, in this case the output is display is included, showing both the pixels) graphics display for any recorded into the animation stills store a individual and the cumulative average computer system with an RS232 serial picture at a time. decay of sound pressure level in deci- interface. The animation stills store bels as functions of time using a The animation stills store provides standard 625/50 television format. A a means of storing up to 815 television computational routine can be initiated, pictures (1630 fields) in digital either manually, after a sufficiently component (YW) form and replaying representative average decay has been acquired, or automatically after a preset number of individual decays. This calculates the average gradient of the decay and hence, the reverberation time in seconds. The numerical result is displayed in a table showing reverberation times and frequency (as third-octave band numbers). Measurements can be made in any of twenty-four, 1/3 octave-wide bands of frequency over the range of centre frequencies from 50 Hz to 10 kHz with Page 4 - 'ENG INF' Autumn 1982 Im Facilities Headphone Limiter

them either individually or as a sequence at normal television rates subject to certain restrictions. Facilities ...... " are also provided to allow pictures to be "

combined by mixing and colour .. separation overlay (CSO) whilst in .. digital form. The main storage medium . . .~. .. is a computer type disc-pack adapted to record and replay at television rates. --- Three semiconductor picture (frame) stores are included to provide . temporary storage of pictures during Single limiter (centre) with case (right) for holding two for stereo. internal processing operations. The self-powered headphone pro- higher than 150dB cause instantaneous The control desk for the tector safeguards both the headphones damage, and prolonged exposure to animation stills. store comprises three and their wearers against excessive sounds in excess of 90dB cause progres- panels and a VDU in a similar layout to levels. It is self-powered and easy to sive loss of hearing as the result of that of the video rostrum camera. install being simply added between the the intense or prolonged high sound Various 'pages' of control information amplifier and the headphones. The levels. can be called up onto the display and device allows a maximum subjective The design of equipment for pro- these allow an operator to program the output before shutdown and its delay- tecting headphone wearers presents a system to replay the desired sequence of ed action gives no distortion of short- number of problems. The variable and pictures. The mixing and CSO facilities term peaks. By using an 'A' weighting extreme peak-to-mean ratio of speech can also be used to combine sequences action, the protector gives no distortion and music restricts the use of simple of pictures to form the final output of safe low-frequency waveforms. Its peak clippers, as their action is audible sequence. foldback action gives a reduction in on peaks of programme, even though Pictures can be loaded into the output once the safety threshold is the average programme level may be stills store either individually or as a exceeded. much lower than the clipper level. continuous sequence at normal Investigation has shown that The energy output of a television rates. This recording listeners choose an appreciably higher conventional clipper circuit continues to operation can be momentarily inter- listening level when using headphones increase with progressive overdrive due rupted at any time in order to check the than when using loudspeakers. Factors to waveform squaring and clipper circuit continuity of movement between sub- leading to this are:- impedances. A condition of any pro- sequent pictures. Any mistakes can 1. A headphone listener may choose a tective device is that no distortion must then be corrected by re-recording. high listening level without disturbing occur until protective action is initiated. After all the pictures have been anyone else. Proposed regulations included in recorded the entire replay sequence can 2. At high levels a loudspeaker - two Stationery Office publications, be viewed. If any changes are then amplifier system distorts and thus gives "Protection of hearing at work"; and necessary, they can be incorporated into warning; a headphone -amplifier system "Code of practice for reducing the the control details of the output does not. exposure of employed person to noise", sequence and the results viewed imm- 3. The physical sensations to feet and used 'A' - weighted measurements ediately. chest provided by a loudspeaker are not (dB(A)) up to the very high sound By retaining the original pictures present when listening on headphones. levels of 150dB or higher. of an output sequence within the stills In addition to this tendency, On demonstration at !BC was a store system, the animation produced operational circumstances may give rise method of limiting the electrical signal can be radically altered wherever to high sound levels in the following fed to the headphones to provide safety necessary. Sequences can be played in circumstances: protection for the wearer and overload reverse and a picture may be held for In broadcasting studios high ambient protection for headphones. This many frames instead of appearing for sound levels lead to higher listening required no additional source of power only one frame in the output sequence. levels, both for effective quality other than that present in the signal In this way, a wide range of different monitoring or balancing operations and itself. effects can be generated using the same for intelligibility of communication The insertion of an 'A' weighting stored pictures without re-recording in the presence of high background network in the control chain allows from the original artwork. noise. higher level of signals at less damaging The sound feed to the headphone frequencies to pass in the main chain system may be subject to disturbance before limiting takes place. . by a person not aware of the resultant A time delay or averaging circuit headphone level. This can occur when a prevents short term peaks from trigger- programme source is selected or level ing the protection. A foldback action adjustment made. If 8 ohm headphones ensures the output level is reduced to a are inadvertently connected to a loud- lower level than the threshold level for speaker amplifier output, sound levels in all levels above threshold. Finally, to excess of 140dB (A) are possible. prevent instantaneous damage a fast Clearly, headphones are acting circuit by-passes the above potentially capable of causing damage frequency-dependent and averaging to hearing. Two forms of hearing circuits for very high level signals. damage can occur. Intense sounds *** 'ENC INF' Autumn 1982 - Page 5 volume, as close an approximation as TV Signal by Fibre Optic possible to the BBC's large high-quality Each fibre has a 50/lm graded index monitor, the LS 5/8. In terms of core. The cladding and a hard lacquer subjective quality, the approximation is coating bring the overall fibre diameter very close indeed; the only concessions 150/lm. The numerical aperture is 0.13 to the larger loudspeaker are a reduction and the loss in the region of 6dB/km. in maximum sound level and the loss of The length is just under Ikm but the about half an octave of bass. system total optical loss is about 20dB The LS 5/9 employs two drive due to the inclusion of several units with a passive crossover and equal- demountable connectors. iser. The tweeter is a proprietary soft- The optical connectors used are dome type of 34 mm diameter; the butt-jointed ferrule connectors of the low-frequency unit is a BBC design with 'epoxy and polish' type. Typical power a 200 mm polypropylene diaphragm losses of 2-3dB can be obtained if the and a high-temperature voice coil. The cabinet is vented, with a volume of 28 Optical fibre cable, laser and a ferrule connectors are assembled with care. litres (I cubic foot). Panel damping is connector. The Transmitter The analogue-to-digital converter achieved by an internal bituminous is a standard BBC design based on a layer, and air damping is provided by a TRW (C08/509). The lining of mineral wool enclosed in thin In 1980 Communications polyethylene to prevent the escape of Department were faced with the composite coded input is sampled at 14MHz and coded into 8-bit words. loose fibres. problem of replacing a couple of The crossover frequency is about obsolete balanced-pair cables. which The sampling frequency is not line or subcarrier locked and the input need 2.4 kHz, with asymptotic rolloff rates were used as vision circuits between about 18dB/octave. The ftlter circuit Television Centre and Lime Grove. In not be a PAL coded signal. At a bit-rate of 280 Mbit/s a semi- includes low-frequency equalisation to the normal course of events these would provide an approximately flat free-field have been replaced by coaxial circuits. conductor laser must be used as the optical source as the rise time of high axial response, ind provision is made to But the current interest in optical trans- compensate in initial setting-up for mission methods coupled with a desire radiance LEDs is too long. The laser chosen can launch a mean power of production tolfrances in relative drive- to gain first-hand experience of this unit sensitivities. technology led to the decision to about ImW into the fibre and the device contains an integral photo diode which is Provided. that it is driven by an replace the balanced pairs by optical amplifier of nominal power not exceed- fibres. British Telecom installed eight used to stabilise the mean optical power against the effects of temperature and ing 50 watts, this loudspeaker will not fibre cables early in 1982. The fibre be damaged either mechanically or length is short by telecommunication ageing. thermally by electrical overload, standards, only about Ikm, but is The Receiver whether momentary or prolonged. The typical of the transmission path lengths The expected optical power at the output of the fibre is about 10/lW and a tweeter is also protected against found within studio complexes. accidental impact by a perforated steel At an early stage it was decided PIN photo diode used with a low-noise GaAs FET amplifier will provide guard. that if possible, the performance of the When driven at a nominal SOW optical circuit should be no worse than adequate sensitivity. The digital-to- (20V R.M.S.) the LS 5/9 will generate the performance of a coaxial link. The analogue converters used are a standard BBC design (C09/506). sound levels in excess of 100dB over the results of a feasibility study suggested frequency range 50 Hz to 16 kHz that the desired performance could be General measured at I metre in a typical achieved by using pulse frequency The interconnections of high- listening room. modulation of the optical source. speed logic devices need careful design. Designs Department have just However, the price of such a link In the critical parts of the transmitter completed design of a new loudspeaker would be high and the. report and receiver three-layer pcbs are used. assembly, the LS 3/4C for close mono- recommended that a more appropriate The central layer is an earth plane and phonic listening. This is intended for use for this circuit would be as an this allows critical interconnections to experimental link for digital trans- be treated at microstrip transmission use in television mobile control rooms mission of composite television signals lines whilst retaining all flexibility of a and similar types of area. Although it using PCM. A single channel system double-sided layout. replaces the LS 3/4B which is now would need approximately 140 Mbit/s, obsolete, it is able to handle higher but a two-channel system, needing 280 powers and has an improved high Mbit/s, is of more interest as the bit rate ... frequency response. is similar to that required for Two new licences have been component coded digital video - the negotiated with Spendor Audio Systems favoured system for use within studios. and Goodmans Loudspeakers for the The link would then provide valuable LS 5/9 et AI miniature monitoring loudspeaker, the experience of high bit-rate digital trans- LS 3/5A. Rogers-Swisstone already mission as well as the experience gained The LS 5/9 was on working holds a licence to manufacture and of optical transmission methods. display in the mobile radio studio at market another BBC designed miniature The System mc. This medium size monitoring monitoring loudspeaker the LS 3/8A. The Fibre and Optical Connectors loudspeaker has been developed for use The cable installed has eight fibres in locations where space is limited, or arranged in four pairs. Each pair is where portability is an inlportant * * * contained within a loose tube, helically consideration. The design objective was wound around a steel strength member. to provide, in one quarter of the cabinet Page 6 - 'ENG INF' Autumn 1982 Colour coded pins set the gain of each The two carrier system uses a Type 5 CMCR cross-point thus enabling any combin- second f.m. sound carrier, between 250 ation of inputs to be mixed, at different kHz and 350 kHz above the existing levels if required, on to an output feed. sound carrier, to carry the extra sound The engineering and camera information. The level of the main control area is at the front and incorp- sound carrier is reduced with the second orates a five position desk. Four of the carrier being at an even lower level. (In positions are camera control points order to improve the compatibility of equipped to control two cameras each, the system with existing receivers). A although for most programmes not all compromise is necessary because if the eight are used. The fifth position is a carrier levels are too low the service area colour balance point where all the for stereo sound will be smaller than cameras are colour balanced from a that for the pictures and existing single routable control panel. The receiver sound stages may not work standard cameras are Philips LDK5s properly. Another matter for A Type 5 CMCR was exhibited operated on triax cable or through a compromise is the frequency of the on the promenade at the IBC at radio link. LDK14L cameras are also second carrier. Choosing higher Brighton. Because of weight restrictions available enabling a lightweight camera frequency improves compatibility but on the promenade, the sound control head to be deployed using the same may worsen adjacent channel inter- desk had to be removed and re-installed cable and camera control equipment as ference and increase the difficulty and when the vehicle was in its final the standard camera. cost of modifying transmitters. position. The vehicle is one of a series The vehicle as displayed was Patterning of the picture and of replacements for the BBC main virtually complete but not completely crosstalk from the extra sound channel television outside broadcast fleet tested. It is one of three to be operated into the main one are compatibility vehicles built around 1970. These from the BBC North base in Manchester problems which can occur due to the earlier vehicles, known as Type 2, have and was exhibited in cooperation with characteristics of existing receivers. covered the bulk of the BBC's major Link Electronics Ltd who were the Two series of test transmissions from outside broadcast commitments BBC's main contractor for the Type 5 Crystal Palace showed that compat- throughout the '70s and into the early fleet. ibility problems may arise with a sign- '80s. They were three compartment ificant minority of receivers. However, vehicles, production, engineering and the samples were too small to be certain sound, and were equipped with five Stereo Sound about the number of viewers who would cameras. be affected. Nevertheless, these tests By the late 1970s outside For some years the BBC has been gave valuable results and Research broadcasts had developed and expanded interested in the possibility of broad- Department are grateful to those who to the point where five cameras were in- casting stereo sound with television, participated. sufficient for many broadcasts and it from the existing network of uhf trans- It is hoped to involve many more was therefore necessary to deploy more mitters. However, the technical diffi- people in another series of test trans- than one vehicle for these programmes. culties are considerable. missions from Crystal Palace planned The Type 5 carrying up to eight One obvious method is to for late October/early November. A cameras, was designed to cope with all transmit a pilot-tone multiplex signal. range of carrier levels and frequency but the most complex broadcasts When this possibility was examined it separations will be tried in order to without the use of additional product- was shown that the multiplex signal is investigate the compatibility aspect ion vehicles. It is a three compartment easy to transmit and causes no compat- further. vehicle with the production area in the ibility problems with existing receivers. In view of the plans to introduce centre. The production desk and However, because of the buzz-on-sound satellite television with digital sound we monitor stack are oriented along the it is far from straightforward to design a might also consider the possibility of length of the vehicle in order to provide stereo receiver that will givegood sound using digital sound with terrestrial adequate elbow-room for a staff of four quality. Furthermore, if a subcarrier of television. One possibility is to add a seated along the desk. This cannot be 38 kHz is used, it beats with line freq- carrier about 500 kHz above the exist- achieved with the more conventional uency and produces intolerable whistles. ing sound carrier and modulate it with a cross-ways layout in a vehicle which is In order to avoid these whistles it is form of phase shift keying. This might restricted by traffic regulations to 2.5 necessary to use a subcarrier, locked to accommodate two sound channels, but metres width. A customised Grass twice line frequency, which may restrict it is likely that a compromise would Valley 16 channel vision mixer is the audio bandwidth that can be used. again be needed over the technical para- installed with monitoring and line The problem of buzz-on-sound meters of the system. routing facilities to match the complex can arise in a number of ways, and In conclusion, the search is on requirements for the production of mostly affects the difference channel. for a two channel system which will give sports and other live programmes which One cause is unwanted phase both hi-fi sound and satisfactory com- are demanding in terms of cameras, modulation of the vision carrier (ICPM), patibility with existing receivers. video tape, slo-mo and caption effects. which is transferred to the 6 MHz sound Attention is presently concentrated on The sound area, at the rear, is I.F. in the intercarrier process. Among the two carrier system, but if compati- equipped with a 24 channel Neve desk the sources of ICPMis the asymmetrical bility proves to be a serious problem with 20 auxiliary channels. The area fIltering of the vision signal which is then other approaches may be tried. also houses the communications equip- applied in all TV receiver I.F. stages. At At this stage there is insufficient ment. This is a BBC design which is present, since it is not clear whether a information to make firm proposals for aimed at total flexibility to cope with satisfactory domestic receiver can be a stereo sound service for our terrestrial all kinds of outside broadcast. Its heart produced, a two carrier sound system is transmissions. This is only the first is a 100 x 50 active peg-board matrix. being tried instead. phase of a long term project.

'ENG INF' Autumn 1982 - Page 7 numbers of the pictures being output. 'continued from Page 1 Studio Stills Store ' Pictures can be selected for transmission The foremost advantage is the reduced The studio stills store, which was either randomly, using a number key. need for adjustment and maintenance, on display at IBC, was a prototype of a pad, or in sequence using a single 'Cut' because solid-state sensors have a long simple, inexpensive, electronic still- button. lifetime and are completely free from picture storage and display system. It Further developments of the store problems of ageing and drift. Other enables still pictures to be selected for are now in hand. These include an advantages are that the telecine is transmission, replacing more increase in the number of pictures smaller and less complex, high voltages conventional slide-scanners. It provides stored, a reduction in the access time are eliminated from the equipment, and storage for pictures derived from slides, flying-spot afterglow is absent as is geo- or "grabbed" from electronic sources and a method of conveying pictures between stores and providing long term metric distortion and variation of focus such as cameras, caption generators and storage using a removable medium. over the field. graphic sources. During field trials at TV Centre, Development of commercial When used with electronic the prototype stills store has been used telecines has been hindered by two sources, the electronic stills store avoids 'live' for several programmes. It has also factors. The first is the scarcity of the time delays and quality losses of the been used in conjunction with the suitable line-array sensors. (It is only in photographic process. A "clean-up" 'Flair' electronic graphics equipment recent years that the quality of these mode removes inter-field movement (see Eng Inf No. 7) to produce a series devices has become high enough for blur from the picture by using inter- polation techniques. When used with of programmes to be broadcast later thi.> them to be suitable for use with the year. wide range of film that must be handled slides, the store removes the need to by broadcasters). The second factor is change slides rapidly on-air and thus that the signals emerge from the sensor allows time for adjustments to be made Test Card F in a non-standard sequentially-scanned to focus and colour balance for ex- manner. In order to convert them to ample. The prototype equipment stores The BBC has radiated Test Card F standard interlaced form, a standards 40 still frames on an 8-inch "Win- during trade test transmissions for a converter incorporating a large amount chester" magnetic disc, and the contents number of years but its future use of storage is required. Although this of the store can be viewed as a became uncertain partly due to the was unthinkable several years ago, the composite "poly-photo" display on the difficulty of obtaining quantities of higll rapidly falling cost of storage, coupled VDU screen. Two independent , quality slides. with the wide use of microprocessors and Blue (RGB) outputs are fed Consultations with the receiver available for control purposes, from two digital luminance (Y), and trade via the British Radio and fortunately means that it is not a sign- colour difference (U and V) picture Electronic Equipment Manufacturers' ificant drawback today. stores, which may be accessed from disc Association (BREMA) revealed that This is especially true if the in 2.5 seconds. An unbroken sequence many service engineers prefer Test Card storage can be used to provide addition- of stills may be obtained by loading F to other purely electronic patterns. al facilities. One facility that can be each store while the other is on-air. This is thought to be because the central provided is full variable-speed running Unlike current slide scanners, the stills picture of a young girl gives a subjective with broadcast quality over a wide may be taken in any order while main- assessment of picture quality and aids speed range and sufficiently good taining this unbroken sequence. the setting of colour saturation. For quality for review purposes at film The disc is loaded by grabbing an future use, Designs Department are speeds up to 400 frames per second. RGB input picture in either of two producing an equipment which stores Another is the use of a fourth optical buffer stores before recording it on the the test card in digital form in order to channel in the machine which is disc. overcome the problems of slide sensitive to infra-red light. This fourth The stills store is controlled by a duplication and the need for a slide channel is able to detect particles of dirt keyboard which can be operated scanner. on the r1lm and suppress their visibility remotely from the equipment. The key- Data will be held in YUV form before transmission. board displays the identification using eight bits and 13.5/6.75 MHz sampling frequencies. All of the geo- metric patterns will be derived from computed picture samples calculated by programs which take account of the requirements for different risetimes in the corner diagonals, the circle and the frequency gratings. This data, which describes an essentially perfect test card, will be combined with the central picture samples obtained by a YUV 'frame grab'; techniques for noise reduction on this central inlage will be explored. Captions for network identific- ation will be added to the complete test card from separate integra] digital generators so that. the one equipment will deliver several differently annotated outputs, aJl of which are coded PAL. The first equipment is expected to be in service by mid 1983.

View of stills store controller.

Page 8 - 'ENG INF' Autumn 1982 Published by BBC Engineering Information Department, and printed by Print Unit, ETD, Wood Norton