High security subscription television system employing real time control of subscriber's program reception

A method of operating a subscription television system, comprising the steps of:

• at a subscriber control unit:
• (a) receiving a complete scrambled television signal which has a video signal component with reversed polarity for at least some fields thereof and which is amplitude modulated on a channel carrier having a first frequency in the CATV channel assignments;
• (b) receiving a coded control signal stream having first portions containing respective subscriber addresses, second portions identifying the channel carrier frequency, and third portions containing scrambling signals which identify the polarity of each field of the complete scrambled television signal, the coded control signal stream being modulated on a code carrier having a second frequency, different from said first frequency, in the CATV channel assignments;
• (c) demodulating the coded control signal stream;
• (d) determining whether one of said first portions of the coded control signal stream matches a local address code, and providing an enabling signal when a match is found;
• (e) tuning a local oscillator to a first local oscillator frequency corresponding to said channel carrier frequency, in dependence on said second portions of the coded control signal stream, when said enabling signal is provided;
• (f) mixing the modulated complete scrambled amplitude modulated television signal with the first local oscillator frequency to produce an intermediate-frequency scrambled television signal;
• (g) mixing the intermediate frequency scrambled television signal with a second local oscillator frequency to produce the complete scrambled television signal amplitude modulated on an RF carrier detectable by a conventional television receiver;
• (h) regulating said first local oscillator frequency such that the complete scrambled television signal amplitude modulated on the RF carrier is maintained at a constant frequency and is phase-stable;
• and
• (i) descrambling the complete scrambled television signal amplitude modulated on the RF carrier to produce a standard television signal amplitude modulated on the RF carrier in a form detectable by a conventional television receiver.

A method of operating a subscriber control unit for use in a subscription television system using coded control signals originating at a central transmitting station comprising:

• (a) receiving any one of a plurality of channels, at least one of which may be in scrambled form;
• (b) receiving and processing coded control signals;
• (c) converting said at least one scrambled channel to a predetermined frequency band in part by tuning a variable frequency oscillator in response to said coded control signals;
• and
• (d) descrambling said converted channel in response to said coded control signals rendering the resultant descrambled channel directly usable on a conventional television receiver, wherein said step of descrambling said converted channel comprises:
• receiving a converted channel signal comprised of an inverted video television waveform;
• amplifying and detecting said inverted video signal to obtain a detected video signal;
• clipping and filtering said inverted video signal to obtain a continuous wave carrier signal;
• and
• modulating said continuous wave carrier signal with said detected video signal to obtain a descrambled channel directly usable on a conventional television receiver.