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In Britain a sort of solution to co-channel interference was frequency offsetting, but this only worked well when the interfering signal used the same system i.e. 405 lines. Problem was a lot of the interference was from foreign stations using 625 or 819 lines which used varying bandwidths, most European 625 systems used negative video modulation & FM sound, but Belgium had some TX's that used positive video & AM sound, French 819 used positive video & AM sound. The British TV set working on 405 lines, positive video & AM sound was totally confused when these signals came in & you'd get a horrible broken up picture & a warbling distorted sound. European viewers I presume had the same sort of problems when 405 line signals came bounding in..
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