Abstract: A CATV scrambling system ultilizes low cost, uncritical, pole mounted components for all subscriber locations and high cost precision components only in subscriber units provided at "premium" subscriber locations. The subscriber unit includes a digital stepped oscillator for generating frequencies that are 1/10 of the frequency of the premium television signals and are supplied, along with data, to a pole unit scrambling station. The pole unit has a microprocessor which interprets the data and opens a switch for premium television signals that are to be received. The digital stepped oscillator output is supplied to a frequency multiplier which produces interfering carrier frequency signals that are injected through a directional coupler into the cable that feeds the subscriber TV/VCR. A broad band default oscillator is activated by a microprocessor in the pole unit when there is no subscriber unit or when the data is not present.

Abstract: Suppressed sync pulses in a scrambled video signal are restored to their proper level in another video signal that is applied to a clamp circuit for controlling the DC level of an amplifier coupled between the head end encoder and the modulator in a CATV system. This prevents the clamp from drifting and changing the DC signal level in the scrambled video signal supplied to the modulator. The encoder supplies a suppression signal that indicates when a sync pulse is suppressed. This signal is used to trigger sample-and-hold circuits to measure the level of the first suppressed sync pulse after a vertical interval and the level of a sync pulse during the vertical interval when sync pulses are not suppressed. The levels are compared and their difference is used to restore the suppressed sync signals in the video signal applied to the clamp.