Multichannel subscription television system
First Claim
1. In a multi-channel television system utilizing suppression of horizontal synchronization and associated horizontal blanking pulses for scrambling a plurality of composite television channel signals for associated ones of a plurality of television channels in the system, apparatus for providing a timing signal in receiver equipment for a subscriber location for use in descrambling a selected scrambled composite television signal, comprising:
- transmitter means comprising first means generating a first continuous wave sinusoidal carrier frequency signal having a frequency fo;
second means generating a plurality of sinusoidal timing reference signals for associated scrambled television signals, each timing reference signal having a different phase (defined by zero crossings thereof) related to that of, and delayed in time with respect to, suppressed synchronization pulses in the associated scrambled television signal;
third means frequency modulating associated ones of a plurality of second continuous wave sinusoidal carrier frequency signals with associated sinusoidal timing reference signals for providing associated modulated carrier signals, at least some of said second carrier signals having different frequencies that are spaced apart in a particular band in the frequency spectrum; and
fourth means being repsonsive to the first and modulated-second carrier signals for combining only the fundamental frequency of the first carrier signal, only the modulated-fundamental frequencies of the second carrier signals, the associated scrambled television signals, and composite television signals for other channels into a first combination signal; and
receiver means of the receiver equipment for receiving the first combination signal produced by said fourth means, and comprising fifth means for selecting a particular scrambled television channel for viewing and producing a control signal associated with and identifying the selected channel;
sixth means for mixing said first carrier signal in the first combination signal with the modulated carrier signal for the selected channel signal in the first combination signal for producing an intermediate frequency (IF) signal for the selected channel modulated with the associated timing reference signal;
seventh means responsive to said control signal for demodulating the modulated IF signal associated with the selected television channel for reproducing an associated sinusoidal timing reference signal carrying timing information in zero crossings thereof about timing of suppressed synchronization pulses in the associated television signal.
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Accused Products
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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Citations
10 Claims
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1. In a multi-channel television system utilizing suppression of horizontal synchronization and associated horizontal blanking pulses for scrambling a plurality of composite television channel signals for associated ones of a plurality of television channels in the system, apparatus for providing a timing signal in receiver equipment for a subscriber location for use in descrambling a selected scrambled composite television signal, comprising:
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transmitter means comprising first means generating a first continuous wave sinusoidal carrier frequency signal having a frequency fo;
second means generating a plurality of sinusoidal timing reference signals for associated scrambled television signals, each timing reference signal having a different phase (defined by zero crossings thereof) related to that of, and delayed in time with respect to, suppressed synchronization pulses in the associated scrambled television signal;
third means frequency modulating associated ones of a plurality of second continuous wave sinusoidal carrier frequency signals with associated sinusoidal timing reference signals for providing associated modulated carrier signals, at least some of said second carrier signals having different frequencies that are spaced apart in a particular band in the frequency spectrum; and
fourth means being repsonsive to the first and modulated-second carrier signals for combining only the fundamental frequency of the first carrier signal, only the modulated-fundamental frequencies of the second carrier signals, the associated scrambled television signals, and composite television signals for other channels into a first combination signal; andreceiver means of the receiver equipment for receiving the first combination signal produced by said fourth means, and comprising fifth means for selecting a particular scrambled television channel for viewing and producing a control signal associated with and identifying the selected channel;
sixth means for mixing said first carrier signal in the first combination signal with the modulated carrier signal for the selected channel signal in the first combination signal for producing an intermediate frequency (IF) signal for the selected channel modulated with the associated timing reference signal;
seventh means responsive to said control signal for demodulating the modulated IF signal associated with the selected television channel for reproducing an associated sinusoidal timing reference signal carrying timing information in zero crossings thereof about timing of suppressed synchronization pulses in the associated television signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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Specification