405-line Television System - History

History

In 1934 the British government set up a committee (the "Television Committee") to advise on the future of TV broadcasting. The committee recommended that a "high definition" service (defined by them as being a system of 240 lines or more) to be run by the BBC be established. The recommendation was accepted and tenders were sought from industry. Two tenders were received: one from the Baird company offering a 240 line mechanical system, and the other from EMI offering a 405-line all-electronic one. The Television Committee advised that they were unable to choose between the two systems and that both tenders should be accepted, the two systems to be run together for an experimental period.

Broadcasting of the resulting BBC Television Service from their Alexandra Palace site began in November 1936, at first time-sharing broadcasts with the 240-line Baird system; however, after three months of trials (in January 1937) the Baird system was abandoned in favour of exclusive broadcasting with the 405-line Marconi-EMI system on VHF. This became the standard for all British TV broadcasts until the 1960s.

It soon became apparent that television reception was also possible well outside the original intended service area. In February 1938, engineers at the RCA Research Station, Riverhead, Long Island, New York, in the USA, were able to receive the BBC signal 5,000 km (3,100 mi) away, due to the signal being "bounced" back to earth from the ionosphere. A few minutes of programming were recorded on 16 mm movie film. This is now considered to be the only surviving example of pre-war, live British television. The images recorded included Jasmine Bligh and a brief shot of Elizabeth Cowell, two of the original three BBC announcers, an excerpt from an unknown period costume drama, and the BBC's station identification transmitted at the beginning and end of the day's programmes.

The BBC temporarily ceased transmissions on September 1, 1939 the day of the German invasion of Poland, as war was imminent. After the BBC Television Service recommenced in 1946, distant reception reports were received from various parts of the world, including Italy, South Africa, India, the Middle East, North America and the Caribbean.

In 1954 the BBC lost its monopoly of the British television market, and the following year the commercial network ITV, comprising a consortium of regional companies, was launched.

Some ITV companies, notably Lew Grade's ATV, proposed broadcasting in colour using a 405-line variation on the NTSC system, but after some trials in 1955-1956 on its Alexandra Palace then on its Crystal Palace 405 lines transmitters, the BBC persuaded the Government that colour should await the introduction of a higher-definition system.

In 1964 the BBC launched its BBC2 service on UHF using only a 625-line system, which older sets could not receive. For several years BBC1 and ITV transmitted using the 405-line and BBC2 the 625-line standard; the only way to receive them all was to use a very complex "dual-standard" 405- and 625-line, VHF and UHF, receiver. This continued until some time after the introduction of colour; dual-standard colour sets were yet more complex.

625-line PAL colour was introduced in 1967.

In November 1969 BBC1 and ITV also started broadcasting in 625-line PAL colour on UHF. As their programming was now entirely produced using the new standard, the 405-line broadcasts served only as a rebroadcast in monochrome for people who did not have the newer receivers.

One reason for the long switchover period was the difficulty in matching the coverage level of the new UHF 625 line service with the very high level of geographic coverage achieved with the 405-line VHF service.

The last 405-line transmissions were seen on January 3, 1985, in Scotland, having been shut down one day earlier in the rest of the UK. This left only the UHF PAL system in operation in the UK. The frequencies used by the 405-line system were initially left empty, but were later sold off, used now for other purposes including DAB and trunked PMR commercial two way radio systems.