33. TECHNICAL PROBLEMS IN TELEVISION

The dominant constraint on broadcasting is the restriction on ether-space - the available wavebands. Most people may not realise how numerous and varied are the communication services needed to run a country, or the need for the closest international control. They are familiar with broadcast sound and television, but are not aware of how heavy is the demand for frequencies by the maritime services, the police, fire brigades, aircraft control, military and certain social services; and by mobile stations, radio telephones and telegraphs, radio astronomers, radio amateurs and many others. It is because all these users have to be accommodated that our public broadcast and television programmes have to be confined within agreed relatively narrow bands.

At present ether-space is allotted in the "medium" and "long-wave" bands for sound radio, but the congestion of stations in Europe is now so great that further ones in these bands cannot be contemplated; the mutual interference is already very serious, especially after dark. The need for more stations has forced research and development into higher frequencies - into the VHF (very high frequency) bands and more recently the UHF (ultra-high frequency) bands.

It must be appreciated that a sound or television signal does not use one single frequency, of so many megacycles per second, but that the signal energy spreads out to cover a range of "sideband" frequencies. In this respect television demands five hundred to a thousand times as much "space" in these bands as does sound, depending upon the number of scanning lines into which the television picture is divided for transmission. The result is that television station wave lengths must be spaced widely apart within these allocated bands.

(from New Scientist, 5th July, 1962)