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High security subscription television system employing real time control of subscriber's program reception

  • US 4,253,114 A
  • Filed: 09/26/1978
  • Issued: 02/24/1981
  • Est. Priority Date: 04/08/1976
  • Status: Expired due to Term
First Claim
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1. A method of operating a subscription television system, comprising the steps of:

  • I. At a central transmitting station;

    (a) generating a standard television signal having a video signal component with predetermined amplitude and polarity relationships;

    (b) scrambling and amplitude modulating successive fields of the standard television signal in a time-coded way so as to provide a complete scrambled amplitude modulated television signal which has said predetermined polarity reversed for at least some fields thereof, and which is amplitude modulated on a channel carrier having a first frequency in the CATV channel assignments;

    (c) generating a coded control signal stream having first portions containing respective subscriber addresses, second portions identifying the channel carrier frequency, and third portions containing scrambling signals which identify the polarity of each field of the complete scrambled television signal;

    (d) modulating the coded control signal stream on a code carrier having a second frequency different from said first frequency, in the CATV channel assignments; and

    (e) transmitting the complete scrambled television signal and the modulated coded control signal stream to at least one subscriber control unit.

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