IMPROVEMENTS IN OR RELATING TO RECEIVERS FOR PLURAL FREQUENCY SIGNALLING SYSTEMS.

摘要

A receiver for plural frequency signaling systems, comprising a pair of frequency recognition circuits 4,5,6 to 11 respectively producing an output if an input signal to the receiver is within one or other of two frequency bands a low pass filter 14 connected to receive the input signal and having an upper frequency limit between the two frequency bands and a high pass filter 18 connected to receive the input signal and having a lower frequency limit between the two frequency bands the outputs from the low and high pass filters inhibiting the outputs from the frequency recognition circuit associated with the higher frequency band and the frequency recognition circuit associated with the lower frequency band reprectively.