Method and apparatus for testing subscribers' telephone instruments in situ under service conditions

Claim 1

APPARATUS FOR TESTING SUBSCRIBERS'' TELEPHONE SETS IN SITU, COMPRISING MEANS FOR CONNECTING THE APPARATUS IN A TELEPHONE LINE BETWEEN AN EXCHANGE AND A TELEPHONE SET, VOICE FREQUENCY ALTERNATING CURRENT MEANS AT THE EXCHANGE FOR APPLYING A REFERENCE SIGNAL TO THE APPARATUS, ELECTROACOUSTIC TRANSDUCER MEANS IN THE APPARATUS FOR APPLYING SAID REFERENCE SIGNAL TO THE TELEPHONE SET DURING A FIRST INSTANCE AND FOR RECEIVING SAID REFERENCE SIGNAL FROM THE TELEPHONE SET DURING A SECOND INSTANCE, ALTERNATING VOLTAGE MEASURING MEANS IN CIRCUIT WITH SAID ELECTRO-ACOUSTIC TRANSDUCER MEANS FOR INDICATING THE RELATIVE PERFORMANCE OF THE TELEPHONE SET DURING SAID FIRST AND SECOND INSTANCE, MEANS FOR SELECTIVELY DIRECTING SAID REFERENCE SIGNAL FROM THE EXCHANGE THROUGH ALTERNATIVE PATHS IN THE TESTING APPARATUS DURING SAID FIRST AND SECOND INSTANCE, AND SWITCH MEANS IN THE APPARATUS FOR SELECTIVELY CHANGING SAID PATH OF SAID REFERENCE SIGNAL THEREBY DETERMINING THE RECEIVING ABILITY OF THE TELEPHONE SET DURING SAID FIRST INSTANCE AND DETERMINING THE SENDING ABILITY OF THE TELEPHONE SET DURING SAID SECOND INSTANCE.