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Television scrambling system

  • US 3,885,089 A
  • Filed: 02/16/1973
  • Issued: 05/20/1975
  • Est. Priority Date: 02/16/1973
  • Status: Expired due to Term
First Claim
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1. A subscription television scrambling and unscrambling system for selectively transmitting a plurality of television programs on a plurality of transmission channels from a central station to each of a plurality of subscriber sites;

  • said system comprising;

    central station equipment comprising;

    first means for deriving a first signal from a first television program signal;

    second means for deriving timing signals from a second television program signal;

    third means coupled to said first and second means for developing a channel switching code in response to the first signal and timing signals;

    fourth means coupled to said third means for enabling the channel switching code to be transmitted to the subscriber sites in the system;

    fifth means having first and second output circuits, said fifth means being coupled to said fourth means for selectively alternating the first and second television program signals between said first and second output circuits at preselected times determined by a sequence of channel switching codes in order to respectively develop third and fourth scrambled television program signals at said first and second output circuits;

    first and second transmitting means respectively coupled to said first and second output circuits for transmitting to each of the subscriber sites the third and fourth television program signals within the first and second transmission channels, respectively; and

    equipment at each subscriber site comprising;

    a frequency converter responsive to the plurality of transmission channels for converting any selected transmission channel to a predesignated transmission channel;

    sixth means for developing signal information in response to each channel switching code received from the central station;

    seventh means coupled to said sixth means for utilizing the signal information therefrom to generate first and second switching signals when a subscriber is authorized to receive a scrambled television program on a transmission channel selected by the subscriber; and

    switching means coupled between said seventh means and said frequency converter for selectively developing and applying first and second tuning voltages to said frequency converter in response to said first and second switching signals, said frequency converter being responsive to the selective application of the first and second tuning voltages for causing the desired one of the first and second television programs to be developed within the predesignated transmission channel.

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