Importance

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Abstract

Suppressed sync TV signals are descrambled by restoring their sync intervals with restoring pulses generated in predetermined time relationship with timing pulses which are transmitted with the TV signals, amplitude modulated on the audio carrier (the center of the sound or audio frequency portion of the TV signal). The timing pulses are derived by intercarrier demodulation of the television signals which are transmitted on a RF (radio frequency) channel so as to avoid loss of the timing pulses in the event of deviation of the RF TV signals in frequency, either on transmission or due to frequency errors in an up/down converter which is tuned to select the RF TV channel. Baseband signals containing the audio portion of the TV signals are envelope detected in a manner to discriminate against changes in the average level of the sound carrier envelope due, for example, to variations between the sound and picture carrier components of the transmitted TV signal, as by a comparator which responds to the difference between the average value of the envelope and the pulses superimposed upon the envelope attenuated 6 dB such that the timing pulses are detected when they reach fifty percent of peak amplitude.

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First Claim