×

Subscription television apparatus and methods

  • US 4,222,068 A
  • Filed: 11/02/1978
  • Issued: 09/09/1980
  • Est. Priority Date: 11/02/1978
  • Status: Expired due to Term
First Claim
Patent Images

1. A subscriber television system for selectively communicating a composite video signal having fields with horizontal trace lines separated by horizontal blanking pulses having front porches followed by horizontal synchronization pulses and the video signal further having vertical intervals separating the fields, the vertical intervals containing vertical synchronization information followed by horizontal trace lines separated by horizontal blanking pulses, the system comprising:

  • (a) video encoder means for randomly inverting the polarity of said video signal by inverting the polarity of a trace line of randomly selected vertical intervals, and by inverting the trace lines of associated fields following said randomly selected vertical intervals, said encoder means further including means for suppressing the amplitude of randomly selected horizontal synchronization and blanking pulses during fields of said video signal to form a scrambled video signal;

    (b) detector means responsive to the polarity of said trace line of said vertical intervals for detecting the polarity of the trace lines of said associated fields, said detector means being further responsive to the amplitude of said scrambled video signal having less than a first amplitude signal during selected time intervals of said horizontal blanking pulses for detecting the suppression of said randomly selected horizontal synchronization pulses, and(c) decoder means responsive to said detector means for unscrambling said scrambled video signal, said decoder means including means for activating a switch for biasing said video signal with a second predetermined amplitude signal for a selected time interval following said detecting by said detector means of suppression of a horizontal synchronization pulse.

View all claims
  • 1 Assignment
Timeline View
Assignment View
    ×
    ×