Sync suppression scrambling of television signals for subscription TV
First Claim
1. In a sync suppression scrambling system in which TV signals are transmitted with sync pulses thereof suppressed, together with timing pulses having a dynamically variable time delay relationship with said sync pulses and together with delay control pulses which represent said time relationship, descrambling apparatus which comprises means for restoring said suppressed sync pulses of said TV signal with restoring pulses, and means for operating said restoring means to generate said restoring pulses in different time relationships with said timing pulses depending upon the number of said delay control pulses which are detected in a given period of time.
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Abstract
Sync suppressed television signals transmitted with timing pulses in dynamically variable time delayed relationship with respect to the suppressed sync pulses are descrambled with a high degree of noise immunity by decoding tag pulses transmitted with the timing pulses into a digital signal representing the dynamically variable time delay relationship in terms of the number of such tag pulses during a predetermined period of time during each field of the TV signal, into a digital signal. The decoding is carried out to provide the digital signal with different values for different groups, each containing a different number of tag pulses. The pulses which restore the sync pulses in the TV signal in each field are timed with respect to the timing pulses in accordance with the value of the digital signal. Dynamic delay variations which vary from field to field or for any selected number of fields, during any selected period of time, may be accommodated in the descrambling of the TV signals and with high noise immunity due to the use of groups of tagging pulses in the decoding of the dynamically varying delays.
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12 Claims
- 1. In a sync suppression scrambling system in which TV signals are transmitted with sync pulses thereof suppressed, together with timing pulses having a dynamically variable time delay relationship with said sync pulses and together with delay control pulses which represent said time relationship, descrambling apparatus which comprises means for restoring said suppressed sync pulses of said TV signal with restoring pulses, and means for operating said restoring means to generate said restoring pulses in different time relationships with said timing pulses depending upon the number of said delay control pulses which are detected in a given period of time.
Specification