Repeater alarm system for indicating failure of an amplifier

Claim 1

IN A COMMUNICATION SYSTEM WITTH A SIGNAL TRANSMISSION MEDIUM INCLUDING FIRST AND SECOND AMPLIFYING MEANS CONNECTED IN PARALLEL BETWEEN INPUT AND OUTPUT CIRCUITS SO THAT THE OUTPUT IS CONTINUOUS IRRESPECTIVE OF THE FAILURE OF ONE OF SAID AMPLIFYING MEANS, A TESTING ARRANGEMENT COMPRISING: CIRCUIT CONNECTIONS TO SAID INPUT CIRCUIT FOR COUPLING THERETO TEST SIGNALS OF A FIRST AND A SECOND TEST FREQUENCY; A FIRST RESONANT CIRCUIT CONNECTED TO THE OUTPUT OF SAID FIRST AMPLIFYING MEANS AND TUNED TO SAID FIRST TEST FREQUENCY SO AS TO PASS ALL SIGNALS EXCEPT THOSE OF SAID FIRST TEST FREQUENCY FROM SAID FIRST AMPLIFYING MEANS TO SAID OUTPUT CIRCUIT; A SECOND RESONANT CIRCUIT CONNECTED TO THE OUTPUT OF SAID SECOND AMPLIFYING MEANS AND TUNED TO SAID SECOND TEST FREQUENCY SO AS TO PASS ALL SIGNALS EXCEPT THOSE OF SAID SECOND TEST FREQUENCY FROM SAID SECOND AMPLIFYING MEANS TO SAID OUTPUT CIRCUIT; AND MEANS CONNECTED TO SAID OUTPUT CIRCUIT FOR DETECTING THE PRESENCE AND ABSENCE OF SAID TEST SIGNALS OF A FIRST AND A SECOND TEST FREQUENCY, FOR INDICATING FAILURE OF SAID FIRST AMPLIFYING MEANS WHEN PRESENCE OF SIGNALS OF SAID FIRST TEST FREQUENCY AND ABSENCE OF SIGNALS OF SAID SECOND TEST FREQUENCY IS DETECTED, AND FOR INDICATING FAILURE OF SAID SECOND AMPLIFYING MEANS WHEN PRESENCE OF SIGNALS OF SAID SECOND TEST FREQUENCY AND ABSENCE OF SIGNALS OF SAID FIRST TEST FREQUENCY IS DETECTED.