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Abstract

A master decoder for scrambled television signals in which the signals are processed in a circuit by converting them to other frequencies and then removing the scrambling signal. One method uses one or more narrow filters at a fixed frequency with the television signal being heterodyned down to the frequency of the filters to place the scrambling signals in the rejection band of one of the filters. A second method eliminates scrambling signals by filters at video frequencies. In this method, the frequency in phase with the television signal carrier of a television channel is regenerated by filtering it with a narrow crystal filter and by means of an automatic phase comparison (APC) loop. The regenerated carrier is then used to synchronously demodulate the television signal. A third method for removing the scrambling signals is by use of one or more comb filters. A comb filter using a delay line produces periodic rejecting bands spaced at selected frequencies which are equal to the reciprocal of the delay produced by the delay lines. The delay lines are video delay lines with a delay of one horizontal line which are used to produce rejection bands spaced by the horizontal frequency.

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First Claim