Cable TV - Scrambling - Gated Sync

Most cable systems have used / or still are using a scrambling method using pulsed sync suppression.

This method involves reducing the amplitude of the picture carrier signal by 6db during the horizontal blanking interval and possibly during the vertical blanking interval. This video signal has sync tips located between the black and white levels. Sync seperators in the television cannot operate properly with this signal, nor can AGC and color circuits, since the picture cannot sync properly the signal appears to be scrambled.

The decoder compensates by attenuating this signal during the time in which the transmitted signal was not attenuated, in which the logic controlled gain switch must receive the timing data for proper sync.

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