Multifrequency signalling device and particularly signalling receiver thereof

摘要

A signalling receiver has a number of selective filters, each selective corresponding to one of the voice frequencies of the signalling plan. Each filter is associated with a detector and a signal envelope detector circuit, and, in turn, these detectors are followed by a shaping circuit for giving the detector a slow rising leading edge wave front and a fast falling trailing edge. The significance of the slow rising wave front is that it tends to limit the signal to the fundamental frequency, as contrasted with a square wave form which tends to have an infinite number of harmonics. The signal received in the signalling receiver is applied either simultaneously with or slightly before the envelope detector circuit. The selective filters have controlled selectivity. The outlet signal from the shaping circuit is applied to the selectivity control means of the filters.