Recollections of BBC engineering from 1922 to 1997
The British Broadcasting Corporation
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Designs Department - Transmission Section
TV distribution by cable
In December 1949 the first regional television transmitting station was opened at Sutton Coldfield. The planning of this station had involved Designs Department in negotiations with the Post Office regarding the cable from London to Birmingham via which the station received its signal and in setting performance standards and making measurements of the performance achieved.
In 1937 the first cable manufactured for the transmission of high definition television signals was laid from various OB points around London to Broadcasting House and thence to Alexandra Palace, and was used on the occasion of the coronation procession in May of that year. The cable was 23 mm in diameter, paper insulated, with twin air spaced (kinked) conductors having a characteristic impedance of 186 ohms.
In 1950 the original EMI repeaters and equalisers of the “EMI balanced pair” were replaced by DD equipment developed by S Padel and D Savage, to give improved performance and flexibility. In its improved form the cable was used for the vast majority of central London outside broadcasts for some sixteen years, including a second coronation procession – that of 1953. During this period it was further uprated for 625 line operation.
Eventually, however, the requirements of colour transmission proved too stringent for the thirty year old cable and the sections in central London were replaced in the mid-1960 by 9.5 mm co-axial cable. The terminal equipment for the new cable was produced by DD and was in daily use in the Switching Centre at Broadcasting House.
An important event in 1954 was the first full scale Eurovision hook-up, when pictures were received from the annual Spring Festival at Montreux. The incoming terminal in this country was at Swingate, near Dover, where RAF radar masts provided a convenient support for the aerials of the cross channel radio link. L E Weaver of DD co-ordinated operations with ORTF in France.
Owing to the propagation characteristics of UHF and VHF signals, the long distance transmission of television signals was not possible until 1959, unless a chain of relay stations were available. Thus transatlantic television, for example, involved the physical transport of tape or film. Now, however, a means was devised, known as “Cablefilm”, whereby a short length of film could be transmitted slowly (i.e. at one hundredth the normal projection rate) via the transatlantic cable by facsimile process. This project was a joint undertaking by Research and Designs Departments, with SP and IJS taking a leading part in the Designs Department effort. To speed the process as much as possible the information content of the transmitted signal was reduced to a minimum, and the resulting film at the receiving end was of inferior definition, but the urgency of an important news item could justify acceptance of this deficiency. The system was of practical use until outmoded by the advent of communication satellites in 1962. Among the outstanding events covered with the aid of “Cablefilm” was the Royal Tour of Canada.
In July 1962 the first active communications satellite “Telstar” was used to transmit video signals across the Atlantic Ocean. The signals originated in the USA, and after reception at Goonhilly, Cornwall, were distributed to nine European countries. Designs Department was involved in three aspects of this exercise. Firstly, collaboration took place with the Post Office and with BBC programme and operational departments over engineering planning and technical arrangements for the Corporation’s participation in the event. Secondly, the Department provided, at short notice, two remotely controlled cameras for the coverage of events in the Goonhilly Down technical areas, where there was insufficient space for camera operators to be accommodated as well as 525 line colour equipment. Thirdly, a member of the Department, IJS visited Washington, USA to take part in the first international meeting of a CCIR study group to determine standards for the transmission of television signals over satellite communication systems.
Following the launching of the “Early Bird” satellite the first live colour programme transmission took place from Europe to the USA on 1 April 1966. Signals from London were routed to Raisting in Germany, via a link tested and equalised co-operatively by Designs Department and NBC engineers, before being relayed via the satellite to New York.
In October 1968 the Mexico Olympic Games were received via the ATS 3 satellite for transmission in the UK and Europe. The manning of the satellite terminal apparatus was shared between Designs and Communications Departments, and some 170 hours of programme were transmitted during the course of the games. The processing of the received signal included standards conversion by means of a Field-Store Standards Converter and, in addition to this, a comprehensive array of equipment was provided for the correction or amelioration of distorted signals.
Sound in Syncs
In 1969 Designs Department undertook the engineering of Research Department’s system for the insertion of a pulse code modulated sound signal into the synchronising periods of a video signal. Prototype “Sound in syncs” equipment was produced and a demonstration of the system given to members of the EBU.
To facilitate the processing of video signals, a high performance semi-conductor switching matrix was developed in 1969, together with the means of paralleling three such matrices while maintaining performance and timing.
13 Channel PCM
In 1972 development was completed of a 13 channel, high quality system for the distribution of sound signals, using pulse code modulation. The system was intended primarily to facilitate the distribution of stereophonic pairs of signals, since the stereo image can be seriously damaged by otherwise insignificant differences of propagation time when the two signals are transmitted by line.