Broadcasting in Britain: The Coming of Television 

2 December 2022 tbs.pm/76320

 

Cover of Broadcasting in Britain

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

The transmission of moving pictures was accomplished only in the 1920s, but still pictures were transmitted over wires by Alexander Bain in about 1850, and in the 1860s a system developed by the Abbe Caselli was operated commercially between Paris and Lyons. In both instances, the complexity of a two-dimensional scene was reduced to a single stream of information for transmission as an electrical signal; this ‘scanning’ principle is the basis of all television.

With the discovery, in 1873, that the electrical conductivity of selenium increased with exposure to light, it became possible in principle to derive a signal from an actual scene, and a number of inventors proposed systems for ‘seeing by electricity’.

The proposal that is best remembered today was that of Paul Nipkow, who in 1884 patented the spirally perforated scanning disc that Baird was to use forty years later; there is no evidence that Nipkow himself ever constructed a practical apparatus. The response of selenium to light is too sluggish to allow the rapid scanning of the scene needed for portraying movement. Moreover, early workers were handicapped by the absence of any form of amplification that would enable the signal from the selenium cell to control a light source at the receiver.

Because of these fundamental limitations, interest in television waned, but was revived by the invention of the cathode-ray tube in 1897. Dieckmann in Germany (1906) and Rosing in Russia (1907), embarked on constructing experimental apparatus in which mechanical scanning at the transmitter was combined with display on a cathode-ray tube. With the technology of the period, there was no hope of their succeeding, but Rosing’s experiments had an indirect result of great importance. As an academic he was able to enlist for his research work on television the spare-time assistance of a young student, Vladimir Zworykin. Their association, lasting from 1910 until he graduated in 1912, inspired Zworykin with the passionate interest in television that was to lead him to the invention of the iconoscope, as related later in this chapter.

Very simple calculations suffice to prove that television inevitably involves much higher frequencies than can conveniently be handled by mechanical systems, and in 1908 a noted consulting engineer, W Campbell Swinton, proposed, for the first time, using a deflected beam of electrons as the scanning medium at the transmitter. In 1911 he elaborated his proposals, describing a transmitting tube in which an electron beam scanned a mosaic of light-sensitive photo-emitting elements, mutually insulated. This was a remarkably close prediction of the way in which Zworykin was to achieve high-definition television by all-electronic means some 20 years later.

Swinton did not attempt to realize his scheme. In 1924, he re-presented his proposals in a lecture to the Radio Society of Great Britain, together with some suggestions for their modernization. In the ensuing discussion, a ‘selenium’ pioneer, Llewellyn B Atkinson, said: ‘I do not believe there is sufficient call for seeing by electricity to lead anybody or any corporation to lay out the large sum of money which is necessary to complete the investigation.’ Campbell Swinton ruefully agreed. [Another speaker was more optimistic: ‘I should advise Mr Atkinson to preserve his relics of 40 years ago very carefully in case they are required for storage and exhibition in one of our national museums when the problem has been solved.’ In 1930, Mr Atkinson did indeed present to the Science Museum relics of his experiments of 1882.]

The low-definition era

Notwithstanding these sentiments, the prospects for television were at that time brighter than ever before, with valves to solve many of the technical problems and the popularity of ‘listening-in’ to suggest a lucrative application.

Experimenters were at work in Germany and America, while in England John Logie Baird was beginning to attract public attention. In March 1925 he demonstrated the reproduction of shadow images during a three-week engagement at Selfridge’s store, and a few months later (using apparatus which he presented to the Science Museum in 1926) scored a notable ‘first’ when he reproduced a recognizable image by reflected light; much less light could be reflected from a subject than could be used in the creation of shadow images, so Baird’s achievement was a significant one. A weakness of the apparatus was that at each moment it only utilized the light falling on the single point then being scanned. Baird’s next step was to overcome this weakness by using a mirror-drum scanner in the light projector, which scanned the subject (otherwise in darkness) with an intense spot of light, enabling an ordinary photo-cell to serve as the pick-up device. This was the basis of the Baird 30-line system, current in the later 1920s and early 1930s, for which the ‘Televisor’ receiver was designed.

 

A woman's face, depicted in light and shadow

A 30-line television picture: As displayed on the Baird ‘Televisor’, the picture was enlarged by a lens to the size shown here, and had the reddish orange colour of the neon lamp employed as a light source

 

In 1928 the BBC came under pressure to co-operate with the Baird company, by making one of its stations available for regular transmissions. The Corporation’s refusal was widely criticized and in 1929, following pressure from the Postmaster General, a transmitter was made available for short transmissions outside normal broadcasting hours. Nevertheless, the Corporation’s reluctance was soundly based. The tiny 30-line pictures, flickering at only 12½ pictures per second, had little entertainment value, nor was any substantial improvement possible so long as the vision signal had to be confined to the narrow band of frequencies that could be permitted in a medium-wave transmission. To transmit a television programme, in vision and sound, would have occupied two channels, which could only have been provided at the expense of current plans for an alternative radio programme. The BBC’s chief engineer, P P Eckersley, made it clear that whenever better pictures were demonstrated, the Corporation would try to transmit them, but that this would be impossible on medium waves.

In the event, Baird did not begin development of a standard higher than 30 lines until 1933, whilst for several years even the task of realizing the full potential of the 30-line system took second place to the launching of a succession of publicity-catching variants: ‘Phonovision’ (signals recorded on gramophone records); ‘Noctovision’ (an infra-red device for seeing in the dark or through fog); transatlantic television; colour television; stereoscopic television; large-screen television (an array of 2,100 small lamps).

By 1931, the quality of Baird’s 30-line pictures had improved sufficiently for the BBC to feel justified in providing a studio in Broadcasting House (opened in 1932), undertaking the production of programmes, and instituting collaboration in engineering matters. There was never any intention of instituting a service on 30 lines however, and Baird was required to issue a warning with all sets and kits of parts that the experimental transmissions might cease after March, 1934. Only a few thousand Televisor kits were ever sold and fewer than a thousand ready-made receivers, though experimenters in many parts of Western Europe are known to have received the transmissions on home-made apparatus. The BBC’s highest annual expenditure on 30-line television, in 1933, was only £7129 [£530,000 today, allowing for inflation -Ed]; the transmissions finally ceased in September 1935 when the establishment of a high-definition service was under way.

High-definition television

From about 1930, several British firms besides Baird’s began investigating television. One of these – the Gramophone Company Ltd – merged with other organizations in 1931 to form ‘Electric and Musical Industries Ltd’ (EMI) which mustered a formidable team of research engineers, under Isaac Shoenberg.

Initially, the EMI team designed receivers using cathode-ray tubes, but retained mechanical scanning for generating the picture signals. As their work proceeded, they progressively increased the number of scanning lines in their pictures, from 120 to 180 and then to 243. They also introduced ‘interlaced’ scanning whereby, though only 25 pictures a second are transmitted, each area of the screen is scanned 50 times a second, causing flicker to be substantially reduced. To achieve this effect, all ‘odd-numbered’ lines down the picture are traced out during one scan, and all ‘even-numbered’ lines during the next. Interlacing is now employed in all television systems.

From 1933, the Baird Company too were experimenting with standards of 120, 180 and 240 lines, though without interlacing. These figures suggest that at this stage EMI and Baird were making comparable progress, but BBC engineers attending demonstrations of the rival systems were consistently more impressed by the EMI apparatus.

In 1932 the EMI engineers began work on an electronic camera tube, as an alternative to mechanical scanning. By virtue of EMI’s link with the Radio Corporation of America (RCA), they had access to work that was being carried out in the RCA laboratories on a revolutionary new’ camera tube, the ‘iconoscope’. This was to prove the crucial factor.

The iconoscope camera tube

The ‘spotlight’ technique of scanning the subject with a moving spot of light, used by Baird, could not be used for distant subjects, and was confined to studio use, since it required darkness. It was, however, the only available alternative to scanning a normally lit scene one point at a time, thereby wasting the light from all other points. This inefficiency became proportionately worse as the standard of definition was raised.

The other major obstacle to high-definition television was the impracticability of mechanical methods of scanning; as the scanning frequency increased, the equipment became progressively bulkier and less manage-able.

Both these obstacles were surmounted by Zworykin’s ‘iconoscope’ camera tube. It utilized light more efficiently, by a principle known as ‘charge storage’, and used an electron beam for scanning, thereby avoiding the need for moving parts.

 

Cutaway of a television camera

Emitron camera, 1936: Unlike modern camera tubes, the Emitron required the electron beam to scan the illuminated side of the ‘target’; this accounts for the characteristic shape of the camera, with the electron gun protruding diagonally, below and in front of the lens. An optical viewfinder was used, in a twin-lens reflex arrangement

 

Vladimir Zworykin, who had worked on television in St Petersburg with Rosing, arrived in the United States as a penniless refugee in 1919. At that period television did not exist as a subject for study in the handful of laboratories with facilities for electronic research, and Zworykin was able to work on television only intermittently over the next ten years. Nevertheless, in 1923, while working for Westinghouse, he demonstrated and patented a pick-up tube embodying charge storage, and soon after moving to RCA in 1930 produced the first iconoscope.

The heart of the tube was a mosaic of tiny photo-sensitive elements sparsely deposited on a sheet of mica, and thus insulated from each other; these elements emitted electrons when acted upon by light. On the back of the sheet was a metallic coating, from which the output signal was obtained, by capacitative coupling to the elements of the mosaic. The mosaic was scanned by an electron beam, and when an optical image was focussed on to the mosaic each element underwent a cyclic process, charging up continuously as a result of the light falling upon it, and being discharged periodically by electrons from the scanning beam.

In practice, only about 5% of the charge generated by the light was utilized, but even with this limited storage the sensitivity of the tube was adequate, though low by present-day standards.

The ‘Emitron’ camera tube, developed by EMI engineers in 1933-4, was based on the iconoscope, but incorporated significant differences in manufacturing technique.

The choice of system

In 1934, EMI and the Marconi company merged their television interests in a new company, the Marconi-EMI Television Company, Ltd., which was thus able to profit from the Marconi company’s expertise in the field of transmission. Since the signal generated by a high-definition television system contains a band of frequencies extending from DC to several megahertz, it could not be accommodated in the wavebands then in use, and new techniques had to be devised for transmitting it in the largely unexplored v.h.f. waveband.

The merger further strengthened the resources ranged against the Baird company which, from an early stage, had been aware of the threat from EMI, and had reacted strongly. In 1933, as soon as it became evident that the BBC was taking an interest in EMI’s achievements, the Baird company made representations to the BBC, the Postmaster General and the Prime Minister, attacking the Corporation on the grounds of EMI’s link with an American company.

It was against this background that the Postmaster General, in May 1934, appointed a Television Committee to advise him on ‘the relative merits of the several systems…’; in practice, this meant the Marconi-EMI and Baird systems. The Committee, after a thorough investigation of technical progress in this country, and also in the U.S.A. and Germany, reported in January 1935.

It recommended that a service be instituted by the BBC, with Baird and EMI equipments used alternately for a trial period. It decreed that ‘the definition should not be inferior to a standard of 240 lines and 25 pictures per second’, and that both transmissions should be readily usable by a single receiver.

The Wireless World expressed itself agreeably surprised that the report had specified so high a standard, and reported that news of its publication ‘fell like a bomb-shell on the ears of American radio engineers’.

It was therefore even more surprising when, only a month after the report was published, Marconi-EMI announced that they were abandoning their 243-line standard and would use 405 lines, 25 pictures per second (interlaced). By choosing more lines they were requiring transmitters and receivers to handle higher frequencies for a given sharpness of picture, and the decision was made with considerable misgivings. The Baird company, still heavily committed to mechanical scanning, elected to use the minimum standard specified.

The two companies installed their apparatus in Alexandra Palace in North London. Marconi-EMI used the Emitron camera exclusively-for studio work, for film transmission and for such outdoor programmes as could be staged within the practical range (1 000 ft) of extension cables linking the cameras to the studio equipment.

The Baird equipment had no provision for outside broadcasting. A mirror-drum ‘spotlight’ scanner was used for close-ups and interviews, and a mechanical flying-spot scanner for film transmission. By this time Baird had belatedly realized that only an electronic camera would be satisfactory for large-scale studio productions, and was experimenting with a camera tube invented by the American pioneer, Philo T Farnsworth. However, the tube did not incorporate the vital principle of ‘charge storage’ and never gave satisfactory results. As a stop-gap, Baird had to use an ‘intermediate-film’ process; the programme was filmed, and its sound recorded, on special film which passed directly into a processing plant and was scanned, still wet, 64 seconds after exposure. The whole structure was bolted to the floor, so that the camera was completely immobile.

The official opening of the BBC’s service – the world’s first regular service of high-definition television – took place on November 2, 1936; as planned, the Baird and Marconi-EMI systems were used during alternate weeks. It was soon evident that the Baird system was markedly inferior, and had less potential for improvement. The official announcement of the exclusive adoption of the Marconi-EMI system came in February 1937.

Overnight, Baird ceased to be a figure of importance on the television scene, though he continued to work on a variety of schemes until shortly before his death in 1946 at the age of 57. He was a man of undoubted vision, and a resourceful experimenter; at a time when established opinion held, quite correctly, that high-quality television was inherently impossible with contemporary resources, Baird had nevertheless demonstrated television of a sort. As a result, he was hailed by the Press and the lay public as a great inventor, and embarked on a decade of euphoric improvization, mistakenly believing that his methods could be refined to produce high-quality pictures. But the scientific facts were against him, and his unwillingness to accept them, which in the short term had operated in his favour, in the long term proved his undoing.

The success of the Marconi-EMI system was primarily due to the development of the Emitron camera, but equally significant was the shrewdness with which the engineers chose the basic constants of the system. Many features of the 405-line standard have since been universally adopted, whilst the standard itself, though obsolescent, has continued to give good service into the 1970s.

 

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