Electrical communication system

Claim 1

A COMMUNICATION SYSTEM COMPRISING A TELEPHONE EXCHANGE CENTRAL OFFICE AND A PLURALITY OF SUBSCRIBERS APPARATUS, EACH INCLUDING A TRANSDUCER CONNECTED TO THE CENTRAL OFFICE BY INDIVIDUAL PAIRS OF SUBSCRIBER LINES, A CONTROL STATION INCLUDING AN OPERATOR''S WHEATSTONE BRIDGE LOCATED AT THE CENTRAL OFFICE AND HAVING FOUR ARMS CONNECTED TO DEFINE TWO PARALLEL PATHS AND A DIAGONAL ARM CONNECTED INTERMEDIATE EACH OF SAID PATHS, TRANSFER SWITCH MEANS FOR CONNECTING SAID BRIDGE TO ONE OF SAID PAIRS OF SUBSCRIBER LINES SAID CONTROL STATION INCLUDING A FIRST SIGNAL MEANS INCLUDING MEANS FOR GENERATING A CONTROL FREQUENCY SIGNAL AND MEANS FOR INDUCING SAID CONTROL SIGNAL IN THE DIAGONAL ARM OF SAID BRIDGE AND AN OPERATOR''S RECEIVING APPARATUS INDUCTIVELY COUPLED TO TWO OF SAID FOUR ARMS OF SAID BRIDGE, SAID SUBSCRIBERS APPARATUS FURTHER INCLUDING WHEATSTONE BRIDGE MEANS AND RELAY MEANS FOR CONNECTING SAID SUBSCRIBERS BRIDGE MEANS IN PARALLEL WITH THE SUBSCRIBERS LINES IN RESPONSE TO SAID CONTROL FREQUENCY SIGNAL, SAID SUBSCRIBERS'' WHEATSTONE BRIDGE MEANS INCLUDING MEANS FOR SENDING A SIGNAL TO SAID CENTRAL OFFICE WHEN SAID SUBSCRIBERS BRIDGE MEANS IS CONNECTED TO SAID SUBSCRIBER LINE.