television standards (was Re: Pravetz 82)

Chuck Guzis wrote: The deployed 405/25 "System A" was monochrome, and was in service from 1936 through 1985. There were some experimental colour broadcasts using NTSC-like colour encoding with various subcarrier frequencies, most notably 2.6578215 MHz. Reportedly the BBC convinced the government to skip colour on 405/25 and wait for a higher-definition system. There were also tests of 625/25 with NTSC-like colour encoding using a 4.4296875 MHz subcarrier, and while that was never adopted as a broadcast standard, it is sometimes seen as a baseband signal and referred to colloquially as "NTSC-4.43". 625/25 broadcast started in 1963, and PAL colour in 1967. Apparently 405 line service was originally called "high definition", by comparison to Baird's electromechanical system. There's a lot of historical information at: http://www.pembers.freeserve.co.uk/World-TV-Standards/ Eric