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TV Technology 2. Television on the Air by Richard G. Elen


Marconi-EMI cameramen, 1937

Marconi-EMI cameramen with Emitron cameras, c. 1937

John Logie Baird's goal of persuading the BBC to work with him on an experimental 30-line television service was not easily achieved. Baird and John Reith, the BBC's Director General, had fallen out when both were students in Glasgow. Whether this counted towards Reith's dislike of television or not, it surely did not help matters, and the BBC stubbornly resisted Baird's overtures. Instead, he turned his attention to the Post Office, which was responsible for broadcast licensing.

Finally, after continuing lobbying of the Postmaster General, Sir William Mitchell-Thompson, by the Baird Company, permission was granted and in August/September 1929 30-line test transmissions began via the BBC's original radio transmitter 2LO, on the roof of Selfridges, from Baird's studio facility at Savoy Hill. Under the terms of the Postmaster General's decision, the BBC was obliged to supply engineering support; initially it also assisted in the making of programmes.

Only a single broadcast wavelength was available, and this could not carry sound and picture simultaneously. As a result, the test transmissions were often announced in sound only and then switched to vision only. Broadcasts took place outside normal broadcasting hours, and the pictures, by modern standards, were terrible. Early viewers were called by phone to tell them what they had been watching.

In March 1930 the second of two transmitters came into service at Brookmans Park as part of the BBC's new Regional Scheme, and it became possible to broadcast sound and vision simultaneously from 30 March, although with 17 miles of cable linking the studio to the transmitter it was difficult to maintain the 15 kHz bandwidth down the line that the vision transmissions required, so picture quality was initially slightly reduced.

There were some notable firsts, however, including a performance of Pirandello's play, The Man with a Flower in His Mouth - the first play to be performed on television in Britain (a play had been broadcast in the States by AT&T two years earlier). It was transmitted on 14th July 1930, and produced with the assistance of the BBC's Programme Branch.

The area that could be illuminated and reproduced with 30 lines was so small that only one actor could appear on 'stage' at a time, with a special 'fade board' of chequered squares slid in front of the photocells when it was necessary for a new actor to appear. If any movements were too sudden, or there were large areas of black in the scene, the system was all too likely to lose sync. The system used a black period at the end of each line for synchronisation of the receiver to the transmitter, and black areas during the course of a line could throw it off.

The BBC Control Board was not particularly pleased with the results. On 22nd July 1930, they decided to suspend programming involvement and continue solely with engineering support, the minimum they were obliged to give Baird under their orders from the Postmaster General. Test transmissions continued in this way until June 1932.

Technical advances

A new scanning system based on a rotating drum with 30 angled mirrors was brought into use, and the photocells improved to the point where they could be mounted on movable stands and angled and positioned carefully, to be used as the equivalent of spotlights. The flying-spot system essentially worked in reverse compared to conventional camera/lighting setups: the photocells picked up light reflected from the subject as it was scanned by a bright beam of light.

The first outside broadcast followed, and then the Derby was televised live in June 1931 and with higher quality the following year. At last, there was a change in the BBC's grudging acceptance of television (though arguably the BBC did not recognise television as approaching equal importance to radio until the advent of commercial TV in Britain in the mid-1950s).

Noel Ashbridge, who had replaced P.P. Eckersley as the BBC's Chief Engineer, advised Lord Reith to take television seriously. Reith responded, and on August 22 1932, after a two-month break in transmissions to allow the BBC to take control of both transmission and programme production, basement studio BB in the newly-completed Broadcasting House was opened, and the BBC began a regular 30-line television service, with vision on 261.3 metres and sound on 398.9 metres medium wave. It was the first time that the BBC had made its own television programmes. Broadcasts continued from Studio BB until 16 February 1934, when a ten-day interruption of programming allowed the studio to be moved from Broadcasting House to a specially converted studio at nearby 16 Portland Place.

In addition to the main flying spot system, there was a second scanner in the control room that was pointed at a horizontal drum holding caption cards - about the size of postcards - which included tuning signals, announcement captions and occasionally more, as the caption scanner's image could be mixed into the image from the main 'camera', for example to add a background to a scene.

Receiver technology improved with the development of mirror-drum-based systems, but the 30-line video was still indistinct, with a pronounced 12.5 Hz flicker - though regular viewers and production staff reportedly got used to it.

Electronic Television

As discussed in section 1, there were originally two approaches to the goal of transmitting and receiving pictures by wireless. One was the mechanical scanning technique based on Nipkow's disc of 1884 and adopted by Baird and other early players around the world. The other, A.A. Swinton's proposal of 1908, relied on a completely electronic system based on the cathode ray tube. Both took time to come to fruition as a result of the lack of technology to implement them. But as the advent of more sensitive photocells had made the mechanical technique possible, so the development of electronic amplification techniques and advances in cathode ray tube (CRT) technology now allowed fully-electronic television to be developed.

As had been the case with mechanical scanning, the techniques were developed by a number of different researchers around the world at more or less the same time, making it difficult to determine who, if anyone, was the primary innovator. Such a determination is further complicated by the fact that many writers on the subject have had some kind of axe to grind, generally to promote their particular champion as 'the inventor'.

The major players in electronic television were undoubtedly RCA under David Sarnoff in the USA and EMI's team under Isaac Shoenberg in Britain. The two companies had a degree of common ownership and a patent-sharing arrangement, but the traditional view - that EMI's research relied heavily on that of the American company - is almost certainly incorrect.

It would appear that Russian émigré Vladimir Zworykin, working for RCA, and EMI's J.D. McGee, working under Shoenberg - the latter being a former colleague of Zworykin and Sarnoff in Russia - developed the first cathode ray 'camera' tubes independently, Shoenberg's group being the more advanced. EMI had previously successfully made CRT-based television receivers - receiving mechanically generated 150-line signals - and ultimately, with the help of all-round genius Alan Dower Blumlein, McGee and W.F. Tedham, managed, secretly at first, to transmit a picture all-electronically across the laboratory in 1932.

EMI's 'Emitron' camera used a light-sensitive mosaic that was discharged pixel by pixel as an electron beam scanned it, the discharge current intensity being proportional to the light falling on the dot. At the receiving end, a CRT's electron beam scanned a phosphorescent screen in sync with the transmitted image, lighting up phosphor dots in the screen when they corresponded to illuminated dots in the camera mosaic.

By the end of November, EMI had shown the BBC a 5 inch-square CRT receiver capable of receiving mechanically generated 150-line transmissions via VHF over a distance of two miles. VHF was chosen for reasons of bandwidth: the higher the definition of a television signal, the more bandwidth it occupies, and the wider the bandwidth, the higher the frequency of the signal required to carry it.

EMI urged the BBC to begin transmissions with their system the following year, but the system was, at this time, capable only of telecine (film to TV) operation and not 'live' television. For this reason, and to avoid potential political problems, the BBC's Sir John Reith preferred to keep the Corporation's research with EMI under wraps.

Despite this apparent setback, Shoenberg did not give up, and when Zworykin published information on his 'iconoscope' in 1933, the EMI team was able to read between the lines enough to know that their 'Emitron' was virtually identical. In fact it was apparently superior to the American development, and Shoenberg is said to have concluded that the EMI had nothing significant to learn from RCA in this field.

Knowing they were on the right course, EMI brought additional resources to bear, working not only on cameras but on higher vacuums and on improving the performance of receiving-end CRTs, developing screens in excess of seven inches across. They also succeeded in producing a blue-white phosphor that gave a true black-and-white display instead of the black-and-green previously demonstrated.

Baird knew by now that there was competition in the wings, and tried to smear EMI by claiming that theirs was an American-controlled invention. Meanwhile, he began to increase the resolution of his mechanical system. The race for 'high-definition' television in the UK was on.

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