Information About405-line |
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Initially the system was used by the BBC from their Alexandra Palace site, 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 . In 1955 the BBC lost its monopoly of the British Television market, when 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 the BBC persuaded the Government that colour should await the introduction of a higher-definition system. In 1964 the BBC launched its BBC Two service on UHF only using a 625-line ( 576i ) system, introducing PAL colour in 1967 . In November 1969 BBC One and ITV also started broadcasting on 625-line on UHF in colour. Thereafter the 405-line broadcasts served only as a rebroadcast in monochrome for people who did not have the newer receivers. Finally in January 1985 broadcasts ceased, leaving only the UHF PAL system in operation. The frequencies left empty were sold off, used now for other purposes including DAB . A few 405-line Videotape s are believed to exist. However, the majority of surviving 405-line programmes are in the form of black and white film Telerecording s, usually with optical soundtracks. 405-line is ''system A'' in the CCIR asignment of Broadcast Systems . The audio uses Amplitude Modulation rather than the Frequency Modulation in use on modern analogue systems. In addition, until the 1950s the system was broadcast in a Ratio of 5:4 and only later changed to the more common 4:3 format. Other analogue TV standards have included 30, 90, 120, 180, 240, 243, 343, 441, 455, 525, 605, 625, 819 and 1125 lines but only the 525 and 625 line standards are still in use today. SEE ALSO
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