Alarm sending and receiving system incorporated in a catv system

Claim 1

An alarm sending and receiving system incorporated in a CATV system which transmits broadcasting signals within one frequency range via a trunk line to a plurality of subscribers, comprising an alarm signal generating means at the subscriber ends of the CATV system for generating an alarm signal in a frequency range lower than said first mentioned frequency range and which can be fully separated from said broadcasting signals, an alarm receiver means adapted to be located at any desirable optionally selected location for receiving the alarm signals from said alarm signal generating means, a bridging means associated with said trunk line and provided with a first coupling circuit means cooperating electromagnetically with said trunk line to pass only said broadcast signals, said bridging means also comprising an input terminal and an output terminal on said trunk line and a first bridging terminal, said first coupling circuit means being operatively associated with said trunk line so as to bridge to said bridging terminal said broadcast signals, said bridging means further comprising a first filter between said first bridging terminal and said output terminal to pass only alarm signals of said lower frequency range, a subscriber''s terminal circuit comprising an input terminal and an output terminal on said trunk line, a second coupling circuit means operatively associated with said trunk line to effect an electromagnetic coupling for said broadcast signals, a second bridging terminal, a second filter between said trunk line and said second coupling circuit means operable to pass broadcast signals to said bridging terminal means, an alarm connection terminal, and a third filter between said alarm connection terminal and said trunk line for passing alarm signals and preventing passage of said broadcast signals, whereby actuation of an alarm generating signal at one of said alarm signal generating means provides a closed circuit for the alarm signal only between said actuated alarm signal generating means and said receiver means.