Importance

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Abstract

Sinusoidal timing reference signals, each of which is associated with a different suppresed-sync scrambled-priority television channel signal, frequency modulate associated carrier frequency signals for producing modulated carrier signals that are combined with a continuous wave (CW) sinusoidal carrier frequency signal. After low-pass filtering to block harmonic frequencies that may interfere with the video carriers of composite television signals, only the fundamentals of the CW and modulated carrier signals are combined with non-scrambled and/or scrambled composite television signals for transmission to subscriber's equipment. In a descrambler at a subscriber location, the CW carrier signal is mixed with the modulated carrier signals to produce frequency modulated IF signals containing timing information for associated priority television channel signals. Upon request of a subscriber, a particular IF signal is demodulated to reproduce a timing reference signal here that is operated on to produce timing pulses that are slightly wider than the pulse width of, and delayed in time with respect to, suppressed horizontal blanking pulses carrying synchronization pulses in the associated scrambled composite television signal. The timing pulses drive a switched attenuator or amplifier for restoring the level of suppressed horizontal synchronization and blanking pulses in the associated scrambled composite television signal, and thereby descramble it.

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First Claim