Recollections of BBC engineering from 1922 to 1997
The British Broadcasting Corporation
web site is: www.bbc.co.uk
Designs Department - Recording Section
In 1948, attention to magnetic recording began when the Department received two EMI recorders, type BTR/1, for evaluation; these were among the first magnetic recorders of professional quality to be manufactured in this country. In the same year, a new disk reproducing desk was designed, coded DRD/1. This was suitable for either 78 r.p.m. or 33 ⅓ r.p.m. standard groove recordings on disks up to the maximum size then used 17¼ inches diameter. The pick up, which by the standard of the times was of light weight, was carried on a parallel-tracking arm fitted with a groove-locating facility.
In 1952 a prototype of an improved EMI magnetic recorder (BTR/2) was received. This machine was capable of being controlled remotely and was widely used in later years in central recording and reproducing rooms. Even in 1966, after internal redesign and transistorisation by Designs Department, the BTR/2 was still considered to be equivalent to the best up-to-date machines.
A method of tele-recording on 16 mm film, the “suppressed frame” system, was developed by JLB and extensive use was made of this to provide a record of the Coronation ceremonies of 1953.
In 1955 a sophisticated disk reproducer was produced, specifically designed for the reproduction of long-playing gramophone records, to replace the modified pre-existing 33 ⅓ r.p.m. reproducers which had been used since these records were commercially introduced. The new reproducer incorporated a high-quality commercial three-speed turntable, with the 78 r.p.m. facility removed, and a then highly regarded crystal pickup cartridge on a well-engineered arm which actuated a mechanical/optical groove-indicating device. A quick starting facility, based on the “drop-start” principle but designed to avoid damage to the delicate fine groove records, was incorporated.
In 1969 it was decided that the Goldring 800 gramophone pickup cartridge was the one best suited to the Corporation’s needs for the reproduction of both monophonic and stereophonic fine groove records. Older reproducing desks were modified to give monophonic reproduction using the new cartridge and a new desk, coded RPS/6, was designed for monophonic or stereophonic reproduction. This had all the facilities of the older desks in improved form and in addition frequency response selection and variable speed operation in the range 10 to 80 r.p.m. as well as the normal fixed speeds of 33 ⅓ r.p.m. and 45 r.p.m.
Portable tape recorder
As part of a trend towards the miniaturisation and increased portability of equipment, a successful light weight portable tape recorder, the EMI type L/2, was still further reduced in weight, and its facilities improved in 1955, by the transistorisation of its circuits. (Later, in 1957, it was adapted for the recording of synchronised sound in conjunction with a motion picture camera.) All the apparatus required for a simple, single-channel outside broadcast was successfully fitted into a small leather-covered hand case of conventional appearance.
Initially the recording of television by the BBC was necessarily on photographic film, which could not be re-used and required time-consuming chemical processing before the recorded material could be viewed. A television equivalent of the magnetic recorder was clearly needed, but its advent was delayed by the necessity to achieve a very high tape-to-head speed in order to record the upper frequencies included in the spectrum of a video signal. Research Department’s experimental Vision Electronic Recording Apparatus (VERA) which recorded on a very fast moving tape, with the higher video frequencies as frequency modulation of a 1 MHz carrier, was considered disappointing.
However, the Ampex Corporation of America demonstrated their quadruplex video tape recorder in 1956, operating on 525 lines.A two inch tape, moving at the normal speed of fifteen inches per second, was scanned transversely by four heads set in the periphery of a rapidly spinning wheel with which the tape was curved into contact under pneumatic pressure; the signal was in the form of the single sideband of a frequency-modulated suppressed carrier and was thus largely immune to the effects of level fluctuations due to commutation, irregularities of head-to-tape contact, etc. The tape speed, head wheel speed and, during reproduction, the accurate tracing of the recorded tracks were maintained by an elaborate system of servo circuits. Series production did not begin until late 1957/early 1958 and the 405 lines version did not appear until May 1958.
In 1956, a demonstration of the Ampex machine was witnessed by Sir Harold Bishop and F C Maclean (then Director of Engineering and Deputy Chief Engineer, respectively). On their recommendation machines were ordered and it is believed that BBC Designs Department received the first BBC machine in July 1958, prior to the first BBC machine going into service at Lime Grove in October 1958 (Rediffusion TV received the first in the UK in May 1958 from Rank Electronics). For BBC use, the machines were modified by Designs Department, notably to enable approximately synchronous operation to be achieved; the servo mechanisms and FM signal circuits were also investigated. Work on the Ampex machines continued over a number of years, resulting in a steady improvement in their performance and adaptability and, as might have been expected, video tape recording became a very important part of television operations.
Stereo tape recorder
In 1966 the occasional transmission of stereophonic programmes began from the Third Programme transmitter at Wrotham. This development made necessary the adaptation for stereo working of two of the four continuity control positions in Broadcasting House, London. Also in the domestic sound service, a start was made on the up-dating of the BTR/2 magnetic recorders, in service since 1952, to enable the lower tape speed of 7½ inches / second to be used and to effect a general improvement in the performance of these machines. The conversion involved the replacement of valve apparatus by equivalent solid state units, the fitting of ferrite heads and a new type of tape drive motor, and improvement of the tape tensioning arrangements.
Slow Motion playback
1966 was the year of the World Cup Football championship and a means was sought of reproducing pictures in slow motion from a standard video tape recording. PR devised an adaptation of an Ampex machine in which the tape was fed at one quarter of its normal speed. By means of a mechanical addition to the machine, a loop in the slow moving tape was drawn past the video head assembly with an intermittent motion, so that each field of the recorded picture was replayed at normal tape speed, and this was followed by a three-field-period interval during which the tape was not replayed and might be stationary or moving either backward or forward with varying speed to maintain the quarter-normal average speed through the machine. During the initial replaying of the single field, the reproduced signal was recorded on a magnetic disk store, and this stored signal was replayed four times to form the output signal of the equipment. Two tracks on the disk were used alternatively, and the timing of the system was such that while each quadruple reproduction of the signal stored on one track was taking place, the other track was being erased and recorded with the next picture field from the tape. Thus each field in turn was displayed four times, giving the required quarter speed reproduction of the tape on display equipment operating at normal 625 line field and line rates. The system proved to have considerable application subsequent to the World Cup Championship, especially in programmes covering sporting events, but unfortunately its performance was not adequate for colour operation and it was superseded by equipment of Ampex design.
Programme Effects Generator
The Programme Effects Generator, designed in 1967, was an assembly of four or six magnetic tape reproducers constructed as modules to nest together. Each could be loaded with a small cassette of tape carrying the required sound effect; loading took two seconds and re-winding was automatic after reproduction. Thus a range of effects could be immediately available and repeated as required.
Vertical aperture correction
The performance of 16 mm telecine machines was improved by the provision of vertical aperture correction units, production models of which became available in 1971. The use of this equipment made the quality of pictures reproduced from 16 mm film acceptable for purposes which had formerly required 35 mm film, so that considerable savings on film stock and new equipment became possible.
Transportable presenter’s desk
The introduction of OB programmes such as Radio One Club (around 1969) necessitated the development of a transportable presenter’s desk to be used normally with a pair of disk reproducers. The desk incorporated three stereophonic tape cartridge machines, three monophonic and six stereophonic channels. It was designed to feed a remote OB engineer’s desk via cables up to 100 metres in length. The reproducing desks contained Gates turntables and 12 inch Gray pick up arms with Goldring 800 cartridges. Speeds of 33 ⅓ r.p.m., 45 r.p.m. and 78 r.p.m. were available, but the pickup stylus had to be changed if 78 r.p.m. coarse grooved records re to be played.
Audio Delay Device
The use of satellites for the transatlantic relaying of television signals created a need for an audio delay device to bring the accompanying sound, received via transatlantic cable, into synchronism with the video signal which was delayed approximately half a second by its longer transmission path via the satellite. To meet this need equipment was developed in which the audio signal was recorded as a circular track on a sheet of magnetic-coated material, resembling that of recording tape, which covered a commercial gramophone turntable. The signal was reproduced by a head which could be positioned around the recorded track so that the transit time between the recording and reproducing heads of a point on the track gave the required delay.