Malfunction monitoring of time-division multiplex pcm equipment

Claim 1

IN A TIME DIVISION MULTIPLEX PCM TRANSMISSION SYSTEM WHICH INCLUDES A TRANSMITTER FOR TRANSMITTING A PCM PULSE TRAIN WHICH HAS BEEN FORMED BY SAMPLING AND CODING THE OUTPUT SIGNALS FROM A PLURALITY OF CHANNELS IN SAID TRANSMITTER, AND A RECEIVER FOR RECEIVING AND DECODING THE TRANSMITTED PCM PULSE TRAIN AND THEN DISTRIBUTING THE DECODED PULSE TRAIN TO A PLURALITY OF CHANNELS IN SAID RECEIVER, A MONITORING SYSTEM FOR MONITORING THE OPERATION OF SAID TRANSMISSION SYSTEM AS DATA IS BEING PROCESSED THEREIN, SAID MONITORING SYSTEM COMPRISING: (A) MEANS IN SAID TRANSMITTER FOR GENERATING UNIFORMLY SPACED PILOT PULSES WHICH HAVE THE SAME PREDETERMINED WIDTH, POLARITY AND AMPLITUDE; (B) AMPLITUDE-MODULATING MEANS IN SAID TRANSMITTER, INCLUDING MEANS FOR INSERTING SAID PILOT PULSES AT PERDETERMINED POSITIONS, INTO THE SAMPLED INFORMATION SIGNALS TO FORM AN AMPLITUDE MODULATED PULSE TRAIN WHICH INCLUDES SAID PILOT SIGNALS; (C) MEANS IN SAID TRANSMITTER FOR CODING SAID AMPLITUDE MODULATED PULSE TRAIN, INCLUDING SAID PILOT PULSES, INTO THE TIME DIVISION MULTIPLEX PCM PULSE TRAIN WHICH IS TO BE TRANSMITTED; (D) DECODING MEANS IN SAID RECEIVER FOR DECODING THE RECEIVED PCM PULSE TRAIN, INCLUDING SAID PILOT SAID AMPLITUDE-MODULATED PULSE TRAIN, WHICH REPLICA INCLUDES SAID INSERTED PILOT SIGNALS; (E) AND DETECTION MEANS IN SAID RECEIVER RESPONSIVE ONLY TO THE PILOT SIGNALS CONTAINED IN SAID REPLICA PULSE TRAIN, FOR DETERMINING WHETHER SAID PILOT PULSES HAVE BEEN DISTORTED BEYOND PRESELECTED LIMITS THEREBY INDICATING WHETHER A MALFUNCTION, INCLUDING UNDESIRED DRIFT IN DIRECT CURRENT WORKING POINTS, HAS OCCURRED IN THE TRANSMISSION SYSTEM.