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Abstract

In a television receiver for a transmission system in which the video signal is scrambled to allow only for its authorized reception, a video signal processor (8) is provided in which the scrambled video signal is de-scrambled. A low rate control data signal present at an output (11) of a sound/data signal processor (10) is employed to periodically set (say once every one or two seconds) a master pseudo random pulse generator (12B) producing an output of pseudo random configuration at frame rate which is used to periodically set a video slave pseudo random pulse generator (15) to produce an output of pseudo random configuration at line frequency. This is applied to an input S of the processor (9) and forms the scrambling key for the line-by-line de-scrambling of the video signal. The arrangement has the advantage that the high rate scrambling key is not produced by the first generator (12B) where this generator forms part of a sub-system (13) and so prevents high rate data being present across the sub-system interface.

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First Claim