Recollections of BBC engineering from 1922 to 1997
The British Broadcasting Corporation
web site is: www.bbc.co.uk
Designs Department - Radio Frequency Section
In 1949 the television coverage of the universities annual boat race from Putney to Mortlake was carried out on a hitherto unattempted scale, with nine cameras in use including some on board the launch “Consuta” following the competing boats. Prior to this occasion, only shots of the start and finish of the race had been possible. The improved coverage was made possible by the use of VHF link equipment provided by Designs Department and by the participation of a team of Designs Department staff under the leadership of TW.
UHF link equipment was designed and produced in the Department in time for the television coverage of the University Boat Race in March 1970. This was the first occasion on which the event was broadcast in colour. The new equipment, as well as being colour capable, replaced earlier apparatus which was bulky and inconvenient. Four of the new transmitters and eight receivers were constructed in Designs Department for use by Television Outside Broadcasts Department.
In 1954 the first of a series of television outside broadcast vehicles known as the “Roving Eye” came into service. It was constructed by Designs Department personnel, led by GWHL, and comprised a standard image-orthicon camera-channel, radio links for video, sound and control circuits, and a motor generator set installed in a 30 cwt Morris van. The camera was mounted in a gun ring on the roof of the vehicle, and the orientation of the aerial was maintained when the vehicle was in motion by means of a gyro-compass.
In 1955, advantage was taken of the progressive miniaturisation of electronic components to produce the first “radio microphone”, with a transmitter and battery-container each comparable in size with a large cigarette packet. This device was of particular use in television, where the freedom of movement which it gave to an artist made a significant change to the pattern of programme planning.
In 1971, a very compact transmitter, tuneable over the range 45 MHz – 65 MHz, was developed for radio microphone use in outside broadcasts. It was constructed in a moulded plastic case, to fit in the user’s pocket, and included a mercury cell battery capable of powering the circuit for six hours.
Television Translators (Transposers)
The problems of television reception in areas of uneven terrain, where pronounced “shadows” occur, were mitigated by installation of the first VHF television translators in 1957(?). They received a relatively weak signal and retransmitted it locally, in a different channel, with increased field strength.
In 1965 the BBC’s first two solid state UHF translators were installed at Hertford and Tunbridge Wells. These translators needed a special series of filters, and the “comb-line” configuration was devised.
In 1971 an Active Deflector was developed for use in situations where, usually for topographical reasons, the field strength of the main transmission was inadequate. It re-transmited without changing the signal’s frequency, and instability was avoided by providing about 95dB isolation between the receiving and transmitting aerials.
Research into stereo broadcasting included a series of full-scale field trials from Wrotham in 1958, using the Zenith-GE pilot tone system. Designs Department put into practical form many of the results of the research, as well as contributing some original ideas.
In 1967 a stereo decoder unit was designed for use with Designs Department’s FM re-broadcasting receiver. It was used for monitoring and checking purposes.
During 1968 stereo broadcasting on Radio 3 began as a regular service from Wrotham, Sutton Coldfield and Holme Moss. Designs Department constructed and supplied eleven receivers for these transmissions, as well as specially modified receivers for installation at Whipsnade to receive the Wrotham transmissions and route them via a SHF link to Sutton Coldfield.
Emergency programme feed
On 19 March 1969 the IBA transmitter mast at Emley Moor collapsed during heavy icing conditions and it was necessary to provide a replacement feed of BBC 2 input signal to Belmont, which was normally fed by radio broadcast reception from Emley Moor. Designs Department co-operated with Transmitter Department and TPID to solve the problem by providing mobile equipment close to Belmont to receive the signal from Waltham Cross and re-transmit it at the Emley Moor frequency – Channel 51.
UHF rebroadcast receiver
A new type of UHF rebroadcast receiver was designed and first put into service at Heathfield in 1970. It used synchronous demodulation, which greatly reduced the degradation of the signal compared with that imposed by older receivers, and it was possible to use two links containing these receivers in tandem.
VHF FM transmitters
In 1970 solid state VHF FM transmitters were designed and installed in the local radio stations at Brighton, Leicester and Nottingham. This range of transmitters had output powers from 5 to 400 watts, the lower powered equipment being intended as drivers for high power valve amplifiers.
To improve the reliability of radio broadcast reception feeds, a two channel diversity receiver was produced and the first unit was installed at Rowridge in 1971 to provide the Radio 3 stereo feed. A similar facility for the television service was provided by a double diversity switch, designed for use with two rebroadcast or microwave link receivers to select the better output signal automatically.
Experimental outside broadcasts
In 1956, the Designs Department experimental outside broadcast team (GWL, JI and FB), carried out of a series of broadcasts from an aeroplane in flight, using apparatus in which printed circuit construction was used on an experimental basis. The co-operation of the Royal Air Force was obtained and a series of trial flights from RAF Watton took place over several months, culminating in a series of four broadcasts at the end of August. Subsequent assignments included broadcasts from a submarine at sea and a helicopter in flight. By the end of 1957, fourteen outside broadcast assignments had been carried out. In the light of the information obtained the weight of the equipment was reduced by a factor of two thirds and improved transmission was achieved by the use of a band V FM transmitter. Some tests were made with a French CSF radio camera.
Stabilised aerial platform
In 1968, a stabilised aerial platform was introduced for use on board ship to maintain the correct orientation of highly directional SHF aerials. It was designed to be connected to the ship’s gyro compass for azimuthal sensing, and contained its own gyroscope for elevational sensing.
UHF Test Set