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,...http://www.google.com.au/patents/US4253114?utm_source=gb-gplus-sharePatent US4253114 - High security subscription television system employing real time control of subscriber's program reception
