General Instrument Corporation

Stephen E Crook

Joseph D Rocci

Marc W Kauffman

A cable TV security system utilizes three radio frequency signals as three data communication channels: one downstream channel and two upstream channels. A headend alarm processor transmits system commands on the downstream channel. A plurality of subscriber alarm units, connected to the cable TV system, transmit messages on the upstream channels to the headend alarm processor. The respective center frequency of both upstream channels is selectable by command on the downstream channel transmitted from the headend. In the event that one subscriber's alarm unit malfunctions whereby a continuous stream of upstream transmission jams one of the upstream channels, the headend alarm processor changes the respective transmitter frequency of the remaining subscriber alarm units to a clear channel frequency. Alternatively, the frequency or frequencies of the malfunctioning unit may be changed. In either case, system security coverage is rapidly restored.

Frequency agile security apparatus

A cable TV security system utilizes three radio frequency signals as three data communication channels: one downstream channel and two upstream channels. The system includes a plurality of individual subscriber security units which transmit respective alarm messages on an upstream alarm channel essentially when an alarm condition is first detected. If two or more subscriber units attempt to transmit simultaneous alarm messages on the alarm channel, the resulting collision causes a garbled alarm message to be received at the headend. The present invention provides respective apparatus in each subscriber's security unit for responding to two unique headend search commands for identifying the respective addresses of the subscriber unit or units which originated the garbled alarm messages. The first of these headend search commands requests that subscriber units with a specified bit in their respective address respond if an alarm condition exists and that subscriber unit did not previously respond to a special headend search command. The second headend search command requests that subscriber units with a specified bit in their respective address respond if an alarm condition exists and that unit did previously respond to a special headend search command.

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Horsham, PA, United States of America

Stephen E Crook