Broadcasting in Britain: The Ascendancy of Television 

23 December 2022 tbs.pm/76612

 

Cover of Broadcasting in Britain

From ‘Broadcasting in Britain’, published in 1972 by HMSO

Immediately after the war there was little indication that within ten years there would be more people in Britain watching television than listening to the radio. In Wireless World for May 1946 there was a small paragraph announcing that the television service would re-open in June*; a slightly longer paragraph in the June issue reported that shortage of wood had so far prevented the production of any receivers.

* The Hankey Committee had recommended in 1943 that, though research into an improved specification (including colour) should be pursued, post-war television should initially retain pre-war signal standards.

Thereafter, British television made slow headway against post-war difficulties. In 1948, there were some 50,000 receivers picking up the Alexandra Palace transmissions, and the BBC was planning to extend the service to the rest of the UK. It was at this stage decided to retain the 405-line standard indefinitely. Though other countries used or proposed to use various other standards, all with more lines, there was at that time no immediate prospect of establishing a common standard, even for Europe. A higher standard would have used up more of the radio spectrum for a given quality of picture, hence aggravating overcrowding of the available wavebands, whilst existing equipment was in any case incapable of exploiting its potential advantage in definition.

Between December 1949 and August 1952 the BBC commissioned four high-powered transmitters, bringing television within reach of about 80% of the population. Over the next four years, seven medium-power stations were added, increasing coverage to 97%. These shared channels already in use by the high-power stations. Mutual interference was minimized by radiating vertically polarised waves from some stations and horizontally polarised from others, by making some of the transmitting aerials slightly directional, and by arranging that nominally identical transmitter frequencies were, in fact, very slightly different; this difference could be chosen to ensure that the interference pattern on the screen was of minimum visibility.

To link the various transmitters, the Post Office installed coaxial cables and microwave radio links, capable of earning the necessary 3-MHz band of frequencies, equivalent to 750 telephone circuits. This ‘simultaneous broadcasting’ network was mostly two-way, so that outside broadcasts could be originated from all parts of the UK and programmes produced in regional studios for national distribution.

 

A TV tube, with an original 50p next to it to demonstrate size

Projection tube, about 1950: It was possible to obtain pictures larger than the screens of contemporary picture tubes, by optically projecting onto a translucent screen an enlarged images of a small but extremely bright picture formed on the screen of a special cathode-ray tube

 

Cameras and studios

The outside broadcast of the wedding of HRH Princess Elizabeth and HRH the Duke of Edinburgh, in November 1947, marked the first use of a new camera tube, the CPS* Emitron, based on the American ‘orthicon’ It was more sensitive than earlier tubes, and was free from their spurious ‘shading’ signals, which had required continual adjustment of correcting controls.

* Cathode-Potential Stabilized.

However, the CPS Emitron had one serious failing. Any excessive highlight in the scene, such as a momentary glint off metal or glass, caused the tube to become unstable. On the viewer’s screen, a white patch spread out from the offending point, obliterating the whole picture, and the camera-tube had to be briefly switched off to restore normal operation. When the 3-inch image orthicon tube became available from America in 1949, its freedom from this fault, and its greater sensitivity, caused it to be preferred to the CPS Emitron for outside broadcasting, though its picture quality was less good. In particular it produced an exaggerated accentuation of sharp edges which, while imparting a useful illusion of resolution to the picture, made it look ‘embossed’. Under studio conditions, where highlights were easier to control, the merits of the two tubes were more evenly balanced, and both types were therefore used.

In 1956, a new design of CPS Emitron overcame the problem of instability, but by this time a tube had appeared that superseded all earlier types and was to maintain its supremacy for the remainder of the ‘monochrome’ era.

This was the 4½-inch image orthicon, developed by the English Electric Valve Company in response to the BBC’s dissatisfaction with the 3-inch tube, which the company had manufactured under licence since 1950. There were sound reasons for expecting that the 50% increase in target diameter, though fraught with problems, would bring about a more than proportionate improvement in performance. This proved to be the case, and the 4½-inch tube achieved great success in both home and overseas markets. The situation was, in fact, the exact inverse of what is commonly supposed to happen; America was importing a British development of an American invention.

In 1949 when the BBC acquired a site at White City for the construction of an ambitious studio centre, the television service was still confined to its two pre-war studios at Alexandra Palace. Interim accommodation was urgently needed, and between 1950 and 1956 eight, new studios were opened in the West London area; one had been a variety theatre, and the rest were converted film studios. A start was also made in providing studios at the BBC’s regional centres.

Over this period, new studio facilities were introduced. Lighting installations were designed for more rapid control than had been needed for film production. Back projection widened the range of scenic effects and electronic switching techniques made possible such special effects, as Lilliputian figures moving within a normal scene. A new type of scanning equipment greatly improved the fidelity with which film could be televised.

 

A man with a bulky tape recorder

A BBC correspondent, equipped for the Commonwealth Transantarctic Expedition of 1956: The portable tape-recorder increased the range of events that radio could cover

 

Telerecording and standards conversion

There was no regular provision for recording television programmes (‘telerecording’) until 1949, and the first six years of BBC television are lost to us. There were also more immediate consequences. A programme could be repeated only by re-staging it, preferably before cast, costumes and settings were dispersed, and evening programmes could only employ performers who were not currently working in the theatre. Without editing, the pace of a production was dictated by practical considerations such as costume changes, whilst any mishaps were mercilessly exposed.

Telerecording was accomplished by filming the programme from the screen of a special high-quality monitor. This basically simple method (which is still widely used for some purposes) is complicated by the difficulty of moving the film from frame to frame without thereby losing part of the picture; the moving spot of light that forms the television image is absent for less than 2 milliseconds between the bottom of one scan and the top of the next. In one design of equipment, produced expressly for the 1953 Coronation, alternate scans from the screen were simply blacked out. Since in television all the ‘odd-numbered’ lines are dealt with during one scan and all the ‘even-numbered’ ones during the next, the film contained only, say, the odd-numbered lines, broadened electronically (by vertical ‘spot wobble’ on the monitor tube) so as to fill in the gaps. This loss of information was surprisingly tolerable, though critical examination of the long-shots in the recording of the Coronation service reveals that people’s eyebrows were only intermittently visible.

The use of film telerecording was restricted by its cost, as well as by the noticeable loss of technical quality it entailed, and it did not affect the predominance of ‘live’ programmes.

One application of telerecording is the international exchange of programmes. Since the line structure of the picture is eliminated in the filming process, no problem arises when different line-standards are used in the two countries involved.

Somewhat similar arrangements were needed for the exchange of ‘live’ programmes involving a change of line standard. The original programme was displayed on a high-quality monitor, again with the gaps between lines eliminated electronically. A camera trained on the screen was operated on the line-standard of the ‘user’ country. The first use of such ‘standards conversion’ apparatus was in 1952, when pictures relayed from Paris were broadcast by the BBC; the systematic exchange of programmes between European countries (Eurovision) began in 1954.

Both in film recording and in the form of standards conversion outlined here, technical quality is lost by having to display the original signal as an optical image and then re-scan that image. In later methods of recording and standards conversion, these processes are avoided.

Receivers

Post-war television receivers benefited from war-time work on radar, but had much in common with pre-war sets. In particular, they still employed long, thin picture tubes with circular screens (reduced to a rectangle by a rubber mask), making for small pictures and large cabinets. The size and weight of a receiver was in part due to its massive mains transformer, which supplied a low voltage for heating the valves and a very high voltage for the picture tube. Around 1950, designers got rid of the transformer by connecting the valve heaters in series across the mains supply and deriving the high voltage from the line-scanning circuit.

When the first regional transmitter opened, some manufacturers produced separate ‘London’ and ‘Birmingham’ models tuned to the appropriate frequencies, but soon sets were produced which could be pre-set by the dealer, to any one of the five BBC channels. It was only in 1955, when an alternative programme became available in the London area, that it became necessary to provide means for the viewer to change channels.

‘Independent’ television

The BBC’s monopoly of television broadcasting was ended by the Television Act, 1954, which provided for an additional service, to be financed entirely by the sale of advertising time. Programmes were to be produced by a number of companies, each with a regional franchise, and radiated by a central body – the Independent Television Authority.

The new service, which became known as ITV, was allocated channels in Band III (174-216 MHz). These frequencies were three or four times higher than those hitherto used in this country for television, and required new designs of transmitters, aerials and receivers. The shorter wavelength of the Band III signals made them less able to bend round obstacles, so that pockets of poor reception within the service area of a transmitter were more troublesome than they had been for the Band I channels used by the BBC. By way of compensation, the smaller wavelength meant that more elaborate aerials could be designed for a given overall size, whilst the more nearly ‘optical’ range of Band III signals reduced interference between transmitters using the same frequency.

In September 1955, just over a year after the Television Act became law, the ITA’s London transmitter was operational, serving over 12 million people. Before the end of 1956, three more transmitters had been commissioned, bringing about 60% of the population within reach of the ITA’s programmes, though as yet only about half of the households with television had sets able to receive them.

Radio

The years just after the war were primarily a period of restoration rather than expansion, though the opening of a ‘Third Programme’, for material appealing only to minority audiences, was a major innovation. The BBC installed high-fidelity disc recorders of its own design, but the future of recording was soon seen to lie in the magnetic tape recorder, which had undergone remarkable development in Germany before and during the war. As early as 1935, a recorder using ¼-inch (6.5 mm) acetate tape with a ferric oxide coating had been marketed in Germany. Its performance, however, had not been up to broadcast standards. It had been improved considerably by the beginning of the war, but it was in 1940/41 that the major breakthrough occurred. Workers at the research establishment of the German broadcasting organization rediscovered the fact (previously known in America and Japan) that both the distortion and the noise level were dramatically reduced if the audio-frequency current magnetizing the tape were augmented by a current at an ultrasonic frequency, rather than by the direct current customarily used. Thereafter, ‘Magnetophon’ tape recorders found increasing application in German broadcasting, as well as for military purposes.

At the end of the war, a limited number of Magnetophon machines were brought to this country; the BBC put a pair into service in the autumn of 1946, for replaying music recordings obtained from the continent. Other machines were handed over to manufacturers so that British versions could be developed, and in July 1948 EMI lent specimens of their first recorder to the BBC for appraisal and for service trials. Though the verdicts were quite favourable there was a further period of trial and deliberation before the BBC first entrusted the ‘repeat’ of a live programme to tape, in April 1950.

By 1955, the BBC had 200 static and mobile tape recorders in service, handling 60% of its recordings.

 

A VHF broadcasting mast

V.h.f. aerial at Wrotham, Kent: The cylindrical structure at the top of the mast radiates the BBC’s three radio programmes

 

Frequency modulation

Before the war Edwin Armstrong (an American engineer with several major radio inventions to his credit) had demonstrated that interference-free reception could be achieved by using the v.h.f. frequency band and frequency modulation (f.m.). (In f.m. the sound signal varies the frequency of the radio wave, whereas in amplitude modulation (a.m.) it varies the magnitude.) Commercial stations using frequency modulation were licenced from the beginning of 1941, and when America entered the war in December of that year, production of f.m. receivers was running at an estimated 1,500 a day.

Before the war ended, the BBC was contemplating the use of v.h.f. transmissions to augment the medium-wave service, but did not regard the case for using f.m. rather than a.m. as having been established. Field trials with low-power transmitters, using both methods of modulation, were started in June 1945. The results were encouraging, but did not yield a conclusive answer to the question ‘f.m. or a.m.?’. An experimental high-power station was therefore built, at Wrotham, Kent, and further tests began in 1950 with the object of resolving this uncertainty, and of providing detailed information on the service area achieved. The results clearly showed frequency modulation to be preferable, and plans for a v.h.f./f.m. service went ahead.

In May 1955 Wrotham began radiating the BBC’s domestic programmes, and was rapidly followed by other stations. By installing a new receiver, a listener within the service area of a v.h.f. transmitter could, for the first time, hear evening programmes without interference; moreover, the fidelity of reproduction was greatly improved.

By the end of 1956, about three quarters of a million f.m. receivers had been sold, but factors that were to inhibit public interest in the new service were already at work. The BBC’s audience-research figures for 1955 showed that most of the evening audience was watching television, whilst in 1956 transistor sets (for medium and long waves only) appeared on the British market, and soon became the most popular form of receiver for the predominantly day-time audience left to radio.

 

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