Theoretical and practical ruggedness of UK teletext transmission

The parameters defining the UK teletext transmission standard were set in 1974 after some two years of intensive theoretical and practical investigations. There were available a multitude of possible combinations of binary signalling schemes, screen formats, character coding and control-coding methods. Many possibilities were assessed before a final choice was made in favour of the 40character × 24row fixed-format synchronous transmission system of the UK teletext specification. The paper discusses the reasons behind the selection of the many parameters defining the UK teletext standard, and why in particular a free-format composite character coding scheme is rejected as quite unsuitable for a broadcast data service. Teletext has been available as a public service in the UK for several years. The soundness of the UK teletext standard is being affirmed by the increasing thousands of viewers who, with a teletext receiver bought at low additional teletext cost, are now enjoying a reliable, error-free, efficient and effective domestic information service.