Zenith Electronics Corporation

Harold E Mann, Iii

John A Lund

Ronald L Forbes

A two channel audio scrambling circuit for a television signal encoding system includes synchronized digital carrier switching means for deriving two suppressed carrier, switched audio signals that are 90 degrees apart, and combining them into a single output signal. A digital phase shifter, supplied with a carrier related to the horizontal line frequency develops properly phased outputs for controlling electronic switches to produce two phase displaced digital carrier switching signals. A plurality of scrambling modes are determined by logic means under control of a vertical interval signal, a video inversion signal and a tone signal input for controlling the digital phase shifter to change the carrier frequency. Complementary decoding circuitry for recovering the so-encoded audio signals is also described.

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Skokie, IL, United States of America

Harold E Mann, Iii