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

摘要

A high security subscription television system which includes the feature of dynamic scrambling and descrambling of cable-connected television signals in response to real-time coded control signals. The system also has the ability to precisely tune the frequency converter unit at the subscriber's site, in response to real time coded control signals provided by a computer at the central transmitting station. Various methods of scrambling and descrambling are described which use manipulation of the video signals at the baseband video level, and also at the RF level. Alternate embodiments of the descramblers include a secondary source for the reference carrier signal required for proper descrambler operation. In an ultra-stable embodiment of a subscriber's control terminal, a single crystal controlled master oscillator is used to control the frequency conversion unit, to provide a clean reference carrier signal for the descrambler unit, and to tune the control signal receiver, thereby removing the need for frequent fine tuning control adjustments, and further allowing simplified system design and fabrication.