Subscriber line monitoring system in electronic telephone exchange - compares transmitted and reflected test signals to determine state of line

摘要

A test signal generator (G) is connected via the exchange four wire selector circuit system (TSI) to the transducer (GA) in the subscriber line terminal equipment (TS). The generator feeds signals into the transmit channel. Reflected signals are passed from the transducer via the receive channel to an evaluating circuit (A) together with a suitably time delayed output direct from the generator. The evaluation circuit constructs a transfer function from the two signals received from which the characteristic curve for the subscriber line is determined. If this curve departs from an established norm a fault is recognised and signalled. A computer (R) carries out the evaluation of the transfer function. If the system operates with digital signals then the test signal generator output passes first through an analog to digital converter (A/D) before connection to the exchange equipment.