Importance

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Abstract

A cable television system includes a headend unit having a plurality of program signal sources, encoders, scrambling circuits, and channel modulators for producing a plurality of program channels modulated at a corresponding plurality of cable system carrier frequencies. An address computer within the headend unit is operative upon the encoders to provide the insertion of a message packet within the vertical blanking interval of the program signals. The scrambler circuits render the program signal unviewable by conventional television receivers. A cable system decoder is coupled to the headend by a cable and includes a conventional tuner, intermediate frequency amplifier and detector. A decoder processor is coupled to a channel selection input and to the tuner to provide channel selection in accordance with a user input. The decoder processor examines the message packet during the vertical blanking interval to determine authorization of the decoder to display the received program channel. A descrambler is coupled to the processor and the tuner IF and detector to descramble the program signal if authorization is detected. A modulator modulates the descrambled signal upon a fixed channel carrier for application to a conventional television receiver.

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First Claim