Disabling circuit of a transmission line amplifier

Claim 1

A disabling circuit of a two-way transmission system that has a direct current path and an alternating current path, said disabling circuit having resistive means connected in series in said direct current path, a control switch connected to said resistive means, a disabling switch connected to said alternating current path, and control means having a pair of input terminals connected to said control switch and an output connected to said disabling switch, said control switch operating to a conductive state in response to current flow in said direct current path; said control means operating in response to operation of said control switch to operate said disabling switch to its state for enabling said alternating current path, and said control switch operating in response to cessation of current flow in said direct current path to operate said disabling switch to its state for disabling said alternating current path, characterized in that said control switch comprises a pair of complementary transistors, each of said transistors having a base, an emitter, and a collector, means for connecting base circuits of said transistors to said resistive means, and the emitter-collector circuits of said transistors being connected in parallel across said pair of input terminals of said control means, a different one of said emitter-collector circuits being conductive for each direction of flow of current in said direct current path.