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TV Technology 1. 'Seeing by Wireless' by Richard G. Elen


Poster advertising public demonstration of television, 1930

Poster advertising Baird's first public demonstration of television, 1930

Early developments that led the way to the practical realisation of television - 'seeing by wireless' as it was originally called - had one thing in common: all were impractical at the time they were initially proposed.

Paul Gottlieb Nipkow proposed a rotating disc scanning system in 1884, which was capable, in theory, of scanning a scene and creating a signal that could be sent electrically. However, it relied on an element to change varying amounts of light into a correspondingly varying amount of electricity to create the signal, and for many years the photoelectric cells required were simply too insensitive to generate a useful variation. In addition, the tiny signals needed electronic amplification, which was to require the development of the triode valve.

A quarter of a century later, in June 1908, A.A. Campbell Swinton wrote to the journal Nature, proposing a system of completely electronic television, based on the recently-developed cathode ray tube. In 1911 he lectured on the subject and published circuit diagrams. Again, the system required electronic amplification and a suitably sensitive opto-electronic device to originate the image.

These two approaches provided the fundamental building blocks of two different television systems, the descendants of which were to fight for supremacy in the establishment of the world's first high-definition television service a few years before the Second World War.

For some time, the mechanical scanning approach was in the lead, and researchers in both the US and Europe made significant advances. However it is generally accepted that the title of 'father of television' goes to Scottish inventor John Logie Baird. Though he was probably working on television several years earlier, while still in Scotland, Baird was certainly capable of sending shadows across his South Coast (Folkestone or Hastings) laboratory in the early 1920s, and may even have experimented with colour scanning techniques at this time. Other researchers, such as Jenkins in the USA and von Mihaly in Hungary, reached the 'shadowgraph' stage at a similar time, but what helped take Baird's apparatus beyond this stage, to the ability to send moving, greyscale images, was his development, with an assistant in Tunbridge Wells, of a superior selenium photocell with dramatically improved sensitivity, capable of reproducing gradations of tone between black and white. There was also a problem with blurred images, which Baird addressed by developing a 'sharpening' system that is not clearly described but apparently contributed to the definition of edges in the image.

Baird with some of his early television apparatus

Baird with some of his early television apparatus

Moving to London, Baird set up his laboratory in Soho, where in October 1925 he achieved a clear, greyscale image for the first time, using a ventriloquist's dummy head, nicknamed 'Stukey Bill', as the subject. He excitedly grabbed an office boy, William Taynton, from a nearby office and put him in front of the system, thereby making his the first human face to be shown on television. Four months later, in January 1926, Baird prepared a demonstration to the Royal Institute and a journalist from The Times.

Baird in fact developed two different mechanical scanning systems based upon the Nipkow scanning disc - a disc with a spiral of holes or lenses through which light was passed. In the first, a bright light was passed through the Nipkow disc and a second, splitter disc (and possibly a third) to illuminate the scene being televised. The varying amounts of light reflected from the scene were picked up by a photocell, which converted the light fluctuations into electrical variations that could then be transmitted. This system was known, understandably, as the 'Flying Spot' system. Its disadvantage was that it was difficult to illuminate more distant objects, so the technique was primarily used in small studios. The technique was later developed to employ banks of photocells. These could be moved and crossfaded to produce apparent changes of lighting in this strange, counter-intuitive system.

It turned out that the flying spot technique was perfect for one particular application, namely telecine - scanning movie films for television transmission - where the fixed plane of the film was easy to focus clearly on, and the intense scanning beam gave surprisingly high quality images. The technique has been used for some types of telecine work ever since.

The second scanning technique required the scene to be illuminated normally, and the rotating scanning discs and lenses were used to allow a photocell to scan the scene.

At the receiving end, the 'Televisor' included a similar pair of rotating discs, synchronised rather imperfectly by using the same mains frequency to drive synchronous motors at the transmitting and receiving ends of the chain. A flickering neon bulb was the light source that helped to build up an image on a small 4in x 2in ground-glass screen, in black and red rather than black and white. At this time, Baird's television system produced an image, scanned vertically, of only 30 lines.

Bell Labs in the USA made their own advances in television technology, sending a mechanically-scanned transmission via telephone lines from Washington to New York, 200 miles away, in April 1927. Baird responded by sending a television signal 435 miles, also by telephone, from London to Glasgow. Then on 8th February 1928, Baird's colleagues Clapp and Hutchinson received short-wave television transmissions in New York from Baird in London - the first transatlantic television broadcast. Baird demonstrated colour television in 1928 and worked on stereoscopic (3-D) systems.

Baird also introduced 'large screen TV' with a 1930 demonstration at the London Coliseum of received images on a 6ft x 3ft 'screen' made up of over 2,000 light bulbs.

He also developed a system called 'Phonovision', in which television signals were recorded on disc and played back into the Televisor. This system could be used to align a receiver prior to receiving a broadcast, or, in theory, for the release of actual content. It was possible to record what was essentially an audio disc carrying TV pictures because Baird's 30-line images were very low resolution, and thus occupied very little bandwidth. Indeed, when Baird started making test transmissions in the UK, he used the medium wave (AM) broadcast band, which has quite a limited bandwidth. Baird also sold Televisors, both as kits and as ready-built receivers, to pick up the transmissions. Top-of-the-line models included a medium wave receiver, while cheaper models could be connected to the audio output of an existing radio receiver.

British television broadcasting had become a reality. Baird's next challenge was to get his system accepted by the only official broadcaster in the UK - the British Broadcasting Corporation.

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