CCIR System A
CCIR System A was the 405-line analog television system used in the UK and Ireland. It began service in 1936 and was shut down in 1982 in Ireland and 1985 in Britain.
How it worked: Each picture had 405 lines. Frames were created by interlacing two fields (odd and even), giving 25 frames per second and 50 fields per second. The line rate was 10,125 lines per second. Video bandwidth was 3.0 MHz, and the video signal was transmitted with vestigial-sideband amplitude modulation and positive polarity, so brighter images used more RF power. Sync pulses used very little power.
Audio was also amplitude modulated and carried 3.5 MHz below the video carrier. The total RF bandwidth for System A was 4.26 MHz, designed to fit into the 5.0 MHz TV channels in Britain’s VHF band, with about 740 kHz of guard space between channels.
Colour experiments: System A never carried official color broadcasts, but trials with NTSC, PAL, and SECAM were conducted in the 1950s. Color tests began in 1954 from Alexandra Palace, though they did not become part of the standard 405-line system.
Legacy: System A was one of the world’s first formal broadcasting standards and helped shape European TV allocation.
This page was last edited on 3 February 2026, at 14:18 (CET).