405-line Television System

405-line Television System

The 405-line monochrome analogue television broadcasting system was the first fully electronic television system to be used in regular broadcasting.

It was introduced with the BBC Television Service in 1936, suspended for the duration of World War II, and remained in operation in the UK until 1985, and was also used between 1961 and 1982 in Ireland as well as from 1957 to 1973 for the Rediffusion Television cable service in Hong Kong.

Sometimes called the Marconi-EMI system, it was developed in 1934 by the EMI Research Team led by Sir Isaac Shoenberg. The figure of 405 lines had been chosen following discussions over Sunday lunch at the home of Alan Blumlein. The system was the first broadcast system in Britain to use interlacing, though EMI had been experimenting with a 243 line all-electronic interlaced system since 1933. In the 405 system the scanning lines were broadcast in two complementary fields, 50 times per second, creating 25 frames per second. The actual image was 377 lines high and interlaced, with additional unused lines making the frame up to 405 lines to give the slow circuitry time to prepare for the next frame; in modern terms it would be described as 377i.

At the time of its introduction the 405-line system was referred to as "high definition", which it was compared to earlier systems, although of lower definition than 625-line and later standards.