Recollections of BBC engineering from 1922 to 1997
The British Broadcasting Corporation
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Designs Department - Studio Apparatus (Television) Section
Inlay and Overlay Processes
By 1952, the Television Service was outgrowing its original premises at Alexandra Palace and expanding into the old Gaumont-British film studios at Lime Grove, Shepherds Bush. To meet the needs of this expanding service, a variety of special facilities and apparatus were developed in Designs Department; one such facility, the “inlay” process, was introduced into service in mid-1953. This process enabled the signal from one picture course to replace that form another over a selected area of the raster, determined by means of a mask placed on the screen of a flying-spot cathode-ray tube. A development of this, the “overlay” process, in effect used the silhouette of the inset scene as the mask, so enabling that scene to consist simply of an object or performer against a plain background. These effects were much used for monochrome television until the later “colour separation overlay” process was devised in 1959 to meet the needs of colour television.
Also during 1954 a member of the Department (FGP) was seconded to the Marconi Wireless Telegraph Company for three months to work with that company’s engineers on their experimental colour television equipment. Following this, work was begun in the Department on the construction of experimental colour monitors and coding equipment. Colour equipment was also borrowed from the Marconi Company so that extensive experiments could be carried out, leading in the Autumn to the transmission of an experimental colour signal to NTSC 405 line standards from the standby transmitter at Alexandra Palace. The work continued into 1955 with the construction of further apparatus, notably a vector scope and an NTSC colour signal encoder for installation at Alexandra Palace. Broadcast tests were carried out in co-operation with BREMA (British Radio Equipment Manufacturers’ Association) to establish compatibility and other factors concerning the NTSC colour television waveform.
Colour separation overlay
Colour separation overlay was first used in 1959 and depended on a difference in colour between the foreground object and its background to produce the switching signal. It was first used in a monochrome programme and subsequently developed for extensive use in the colour television services. It was at about this time that transistors began to be used extensively in designs for new equipment.
Remotely controlled camera
In 1960, development was completed of a remotely controlled camera, and the construction of eight such cameras was put in hand for use in the News Studio at Alexandra Palace and the Presentation Studio at the new Television Centre. In co-operation with SCPD (then designated P & ID) a desk was devised from which four such remotely controlled cameras could be operated by two men.
In 1960, Designs Department provided equipment for an exhibit of 405 line colour television at the annual Radio Exhibition.
In 1962 TW visited France to study the SECAM system of colour television. At the year’s Radio Exhibition, 625 line colour television was shown, with equipment provided by Design’s Department.
Selection of Colour Television System
In 1962, the relative performance of the three colour television systems, NTSC, SECAM and PAL, was studied by the television group of Designs Department. In July demonstrations were given in London to an international gathering of the colour experts of the EBU. The staging of these demonstrations entailed the close co-operation of P&ID, Television O & M and Designs Department. Unhappily, no one system was agreed upon for the whole of Europe; in parts of the Continent the PAL system was used, and in the remainder the SECAM system.
Investigation continued into the relative merits of the various systems of colour television, and during 1964 four series of demonstrations were given. The first of these was to a special meeting of CCIR Study Group XI. The performances of all these systems in the presence of various distortions was demonstrated, as well as video tape recordings. The second series of demonstrations were staged in Hamburg in collaboration with members of the EBU; pictures originating at Lime Grove to NTSC standards were displayed in Hamburg using a prototype NTSC decoder. The third series of demonstrations were to an EBU committee and featured the latest developments in video tape recording. The fourth series were given to an EBU Ad-hoc Colour Group and representatives from OIRT. Among the features shown were radio tape recording, including the process of transcoding to PAL standards, the use of a differential phase corrector for NTSC signals and the long distance transmission of the three systems over a loop via Rome.
Colour television tests were also made between London and Moscow. Four members of Designs Department staff travelled to Moscow, with equipment, to demonstrate to leading engineers and politicians an improved NTSC system side-by-side with the PAL and SECAM systems.
In 1965, Designs Department took part in further comparative tests of the colour television systems, and as a result of these tests the Television Advisory Committee made a firm recommendation to the Government that the PAL system, with 625 line definition, should be adopted as standard. Accordingly, colour test transmissions began to be radiated to PAL standards.
A second expedition was made to Moscow to take part in further test transmissions of colour signals between there and points in eastern and western Europe.
Public demonstrations of PAL colour television
During 1967 the Department co-operated with Enineering Information Department and BREMA (British Radio Equipment Manufacturers’ Association) to provide a series of public demonstrations of colour television reception in various towns. Among the more attractive items shown were transmissions in colour from the tennis championships then in progress at Wimbledon; for this assignment coders, decoders, mixers and test equipment were supplied by Designs Department. A colour capable Vertical Aperture Corrector was also introduced into service in 1967.
Designs Department produced a slide scanner in 1971 and the prototype was installed in Studio E at Lime Grove. The scanner was intended to be a low cost device for use in small regional installations, but it was highly reliable and incorporated a number of novel features. There was random access to any of twenty slides, the maximum change time being one second. The mechanism could be controlled remotely, and the whole equipment was contained within a standard sized bay.
In 1972, a second slide scanner was installed in Studio E, together with a control panel for the operation of the two equipments. The panel carried two banks of 20 slide selection switches, an ADVANCE button and fader control for each machine and a CUT button. Cross fades were possible by the simultaneous operation of the fader controls, and when either of these controls was moved to its “fully out” setting the slide carrier of the corresponding scanner is advanced one slide position. Hence, repeated cross fades could cause the entire sequence of forty slides in the two scanners to be shown in turn, the scanners contributing slides to the sequence alternately. Repeated cuts caused a similar pattern of presentation.
Portable colour picture monitor
To provide an easily portable colour picture monitor for use, for example, by outside broadcast commentators, a small commercial colour receiver was modified to accept input signals from line as an alternative to the normal RF input.
Thin Film Circuits
In the interests of compactness and accurate reproducibility of matched value components, increasing use was made of thin film circuit “packages” in 1972. Resistor matrices were developed, in collaboration with a commercial manufacturer, which could be used with integrated circuit operational amplifiers to form the coder and decoder circuits of a colour television system.