Adaptive video descrambling system
First Claim
1. A television decoder for descrambling a scrambled video signal in which the synchronizing signals are suppressed and which includes an unsuppressed reference level occurring during a preset reference interval, said decoder comprising an input terminal for receiving the scrambled video signal, first means operatively connected to said input terminal for detecting the level of the suppressed synchronizing signal, second means operatively connected to said input terminal for detecting the unsuppressed reference level, means operatively connected to said first and second level detecting means for operatively comparing the suppressed synchronizing level and said unsuppressed reference level and for producing an error signal having an amplitude proportional to the difference between the suppressed synchronizing level and said unsuppressed reference level, and means operatively connected to the output of said comparing means for applying said error signal to a second level establishing means in advance of said first detecting means, thereby to modify by an amount based on the amplitude of said error signal the level of the suppressed synchronizing signals.
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Accused Products
Abstract
A television signal is scrambled by suppressing horizontal and vertical synchronizing signals while leaving unsuppressed a reference level during a selected reference interval. Descrambling of the received scrambled signal is achieved by comparing the unsuppressed reference level with the suppressed synchronizing signals and by adding a level representative of that comparison to the suppressed synchronizing signals, thereby to restore the latter to their proper levels.
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Citations
18 Claims
- 1. A television decoder for descrambling a scrambled video signal in which the synchronizing signals are suppressed and which includes an unsuppressed reference level occurring during a preset reference interval, said decoder comprising an input terminal for receiving the scrambled video signal, first means operatively connected to said input terminal for detecting the level of the suppressed synchronizing signal, second means operatively connected to said input terminal for detecting the unsuppressed reference level, means operatively connected to said first and second level detecting means for operatively comparing the suppressed synchronizing level and said unsuppressed reference level and for producing an error signal having an amplitude proportional to the difference between the suppressed synchronizing level and said unsuppressed reference level, and means operatively connected to the output of said comparing means for applying said error signal to a second level establishing means in advance of said first detecting means, thereby to modify by an amount based on the amplitude of said error signal the level of the suppressed synchronizing signals.
Specification