Frequency agile security apparatus

摘要

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.