Television signal scrambling method for CATV system

A transmitting device for a central facility in a community antenna television system for scrambling signals transmitted from said central facility comprising:

• a transmitter;
• a plurality of scrambling circuits, at least some of said scrambling circuits employing different scrambling modes;
• a source of television signals coupled to inputs of said scrambling circuits;
• a scrambling change-over switch circuit having inputs coupled to receive outputs of said scrambling circuits and an output coupled to said transmitter;
• and switch control means coupled to a switch control input of said scrambling change-over switch circuit for selecting at different times different ones said scrambling circuits.

A terminal unit for use with a community antenna television system in which signals are transmitted from a central facility of said community antenna system utilizing one of a plurality of selectable scrambling modes comprising:

• a signal receiving circuit;
• a plurality of descrambling circuits, a different one of said scrambling circuits being provided for each of the scrambling modes which may be transmitted at different times by said central facility;
• means for coupling an output received signal from said signal receiving circuit to inputs of each of said descrambling circuits;
• a descrambling change-over switch circuit having inputs coupled to receive outputs of said descrambling circuits;
• and means coupled to a control input of said descrambling change-over circuit for selecting at each of said different times the one of said descrambling circuits which corresponds to the transmitted scrambling mode.