TRANSMISSION SYSTEM WITH IMPROVED TONE DETECTION

摘要

In a transmission system a pair of signalling tone signals is transmitted by a transmitter (2) to a receiver (6) via a transmission channel (4). In the terminal (6) a tone detector is used to detect the presence of the pair of signalling tone signals. In order to improve the reliability of the tone detector in the case of differing strength of both tone signals, the decision on the presence of the pair of signalling tone signals is based on a combined strength measure which is determined by the adder (23). The combined strength measure is compared with a reference level TH2. In a further embodiment also a check on the level of the individual tone signals is done with comparators (11) and (9), in order to specify the maximum strength difference tolerated.