Enhanced security for a cable system

A method of operating a cable television plant including a cable head-end and a plurality of subscriber terminals, each of said subscriber terminals having single mode signal descrambling means that is either ON or OFF and microprocessor control means comprising:

• transmitting a scrambled television signal including a first and a second mode signal therein to said subscriber terminals;
• transmitting an encoded mode control signal in said scrambled television signal to said subscriber terminals;
• transmitting, apart from said scrambled television signal, a mode control signal decoding algorithm to said microprocessor control means from said cable head-end;
• supplying said encoded mode control signal to said microprocessor control means for decoding;
• supplying said first and said second mode signals to said signal descrambling means;
• turning said signal descrambling means ON and OFF responsive to said first and said second mode signals as validated by said encoded mode control signal;
• and
• periodically changing said encoded control signal to validate said first mode and said second mode signals.

A cable television system comprising:

• in a transmitter;
• a source of video information;
• means for selectively inverting the video information from said source;
• means for supplying a first mode signal and a second mode signal indicative of the inversion/non-inversion of said video information;
• means for supplying an encoded mode control signal for validating one of the first mode and said second mode signals;
• means for multiplexing said video information, said first mode and said second mode signals and said encoded mode control signal and transmitting a multiplexed signal to subscriber stations;
• means for providing a decoding algorithm for said encoded mode control signal apart from said multiplexed signal;
• in a receiver;
• means for receiving said multiplexed signal and supplying said first mode and said second mode signals to an inverting/non-inverting amplifier;
• a microprocessing means;
• means for supplying said decoding algorithm to said microprocessing means;
• means for decoding said encoded mode control signal in said microprocessing means;
• and
• means responsive to decoding of said encoded mode control signal for validating said first mode or said second mode signal for controlling said inverting/non-inverting amplifier to invert or not invert the received video information.