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TV Technology 3. High Definition by Richard G. Elen


Marconi-EMI studio at Alexandra Palace, 1936

The Marconi-EMI studio at Alexandra Palace, 1936

By 1934, the battle to develop a workable high-definition television system for the UK was on, with John Logie Baird and mechanical scanning on one side, and Shoenberg's EMI group with all-electronic television on the other. Baird had taken an early lead with the flying-spot scanner for telecine and moved towards CRT-based receivers, but EMI was catching up.

By this time, major organisational changes had taken place at Baird Television Ltd (BTL). After funding shortages, a takeover had been engineered in 1932, with control passing to Isidore Ostrer and the Gaumont-British Film Corporation. A year later, a boardroom coup ousted Baird from his duties, though he retained the title of managing director - it was felt that while Baird was certainly the father of television, he was focusing too much on mechanical techniques, whereas the future, it was believed, lay in electronic approaches.

Captain A.D.G. West, formerly an engineer at the BBC and EMI, was now technical director, and it was he who began to crank up the resolution of the mechanical scanning system, employing faster rotating discs in a vacuum to improve performance. BTL had moved, in July 1933, to a new facility at The Crystal Palace in Sydenham, South London which was rapidly being equipped as a world-class television station and receiver manufacturing plant, while Baird was effectively banished to the laboratory attached to his new house nearby, free to develop new technologies but effectively locked out of the day-to-day running of the company and brought out primarily to meet the press.

EMI showed a 120-line all-electronic system to the BBC and to the GPO, who regarded it as superior to BTL's latest effort, which was now also offering 120-line images, telecine and a CRT-based electronic receiver using cathode ray tubes built under licence from GEC. Initial EMI electronic transmission demonstrations to management in early 1934 were, however, disappointing. Their mechanical transmission system was now up to 180 lines and the electronic images, initially, were vastly inferior. BTL's, meanwhile, increased the number of lines to 180 and began to use VHF for additional bandwidth, as EMI was already doing.

But by April, EMI had dramatically improved the performance of the Emitron camera tube and was achieving significantly better results. Shoenberg's team built a vision mixer with six channels - two telecine and four cameras - and was able to run a camera outside the Hayes factory by the local canal, as well as studio-based cameras and film sources to show the system off when the BBC visited on 18 April 1934.

The BBC's Engineer In Charge of Television, Douglas Birkinshaw, quoted in Bruce Norman's Here's Looking At You, noted: "No whizzing discs, no mirror drums: silence, lightness, portability. It showed the way things were going. It was quite easy to see, even then, that the Baird system couldn't eventually lead anywhere." He felt that it was inevitable that TV would have to provide outside broadcasts, and with the Baird system's heavy, fixed equipment, this didn't seem possible.

Baird's flying spot system had proved particularly successful for scanning film, thanks at least partially to the absence of focus and depth of field issues - so much so that flying spot scanning remained the standard telecine technique for decades. Following this success, Baird had borrowed an idea from his licensees in Germany, where they used a film camera to shoot studio images, the film going instantly into baths of developer, fixer and then water, being scanned while underwater by a flying spot scanner.

The British implementation of the system - called the 'Intermediate Film Technique' - worked, some of the time, but it had problems: underwater air-bubbles interfered with the sound, and it needed lethal cyanide developer to get the processing time down to 'almost instantaneous' - in fact it took just under a minute. The lurid orange developer was notorious for leaking out of the system and on to the studio floor. The in-line processing and scanning equipment made the assembly so heavy and bulky that it had to be mounted in a special bay-windowed room in the studio where it could not be moved, in stark contrast to EMI's comparatively small, light Emitrons.

BTL, obliged to begin to consider electronic transmission technologies, somewhat half-heartedly struck up a relationship with American Philo T. Farnsworth, another claimant to the title of 'Inventor of Television'. Farnsworth's system, despite major flaws that Baird might have been able to sort out, did produce electronic pictures, but it needed extremely high light levels and BTL was seldom able to get it to work properly, necessitating personal visits from Farnsworth to tweak the temperamental machinery. Part of the deal with Farnsworth, however, gave BTL access to useful electromagnetic deflection technology for CRT-based receivers

High-Definition Considered

In mid-1934, the government set up the Selsdon Committee, under the chairmanship of Postmaster General Sir William Mitchell-Thompson, now Lord Selsdon, and including BBC, government and GPO representatives. Its job was to evaluate the possibility of replacing the existing 30-line low-definition service with a high-definition successor, and which system to use to do so. BTL and EMI were not the only players, with alternative offerings from companies such as Cossor and Scophony and a couple of others, but it was evident that the first two were the primary contenders.

BTL was by now offering an array of technologies, including 30-line flying spot, Intermediate Film at 180 lines and telecine at 240 lines, 25 frames per second, all using mechanical scanning. There was also the Farnsworth all-electronic option - if they could iron out its problems. Its Crystal Palace facility, though at this time out of the limelight, was enormous, and represented the most fully-equipped television studios in the world. Now making regular test transmissions at 180-line resolution, BTL, in April 1934, murmured about applying for a licence as an independent broadcaster, transmitting from the top of the South Tower at the Crystal Palace, over 600 feet above sea level and in view of seven counties, at a power that would cover the entire Greater London area.

EMI, having now set up a joint operation with Marconi to provide it with transmission capability, was officially offering 240-line mechanically scanned telecine and little else - its electronic system was still effectively in its infancy. In an almost incredible leap of faith, Shoenberg decided to take the plunge and committed the Marconi-EMI team to delivering 405 lines, 50 interlaced fields per second - and, giving up drum scanning, to all-electronic signal generation. It was a major milestone. It was also beyond the team's capabilities at the time of the announcement, and it was likely that the first receivers would not do the system justice. Marconi-EMI had specified a system that allowed room to grow - but one that would be difficult to achieve so early in the game.

The difference provided by the interlaced field system was that while the Baird approach delivered 25 complete 'pictures' per second, one after the other, the EMI system sent two 'fields' - one containing alternate lines in the picture and the other filling in the gaps - in the same length of time. So although both sent 25 complete pictures per second, the EMI system, with its 50 interlaced fields per second, was much less subject to flicker. Moreover, having almost twice as many lines made the line structure much less apparent. In fact, the structure of the EMI television signal was so carefully thought out that it became the basis for television standards all over the world for many years to come.

The Selsdon Report was published on 31 January 1935, and Lord Selsdon announced that there would be a high-definition (defined as a minimum of 240 lines, 25 frames: the limit of the Baird system) BBC Television Service - but as the Committee couldn't (or wouldn't) decide between Baird and EMI, it chose both. The two systems would run side by side, alternating weekly, under evaluation for six months, after which a permanent system would be chosen.

After the event, it became evident that there had been political motives behind this complex, wasteful, expensive and perhaps typically British compromise. Baird was a high-profile figure, who had even impressed the Prime Minister with a demonstration. Leaving him out of the world's first high-definition television service would have resulted in serious public criticism of government and Post Office alike. In addition, the bankruptcy of BTL was seen as a real possibility, and once again the government did not want to shoulder the blame for such an eventuality. Finally, including BTL in the BBC Television Service would perhaps help dissuade the company from going it alone.

The day after the Report was published, however, journalists were shown around the previously little-known, but extremely impressive, Crystal Palace facility. Geoffrey Edwards, the News Chronicle radio correspondent, wrote on Saturday, February 2, "Any search by the BBC for a site for the promised London Television station would, it seems, be a waste of time when the Crystal Palace station is there ready for use." But it was not to be. (As a further blow, on 11 September 1935, the BBC closed down its low-definition service, orphaning the several thousand medium wave 30-line mechanical Televisors already in the marketplace. They would never receive programmes again.)

High-definition TV was coming to London, and the BBC had just eighteen months to do it. Gerald Cock, formerly the BBC's outside broadcast director, was appointed Director of the new BBC Television Service.

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