Tone detector and multifrequency receiver using said detector

Abstract From the Canadian patent

The purpose of the receiver is to indicate the reception of a multifrequency signal and to identify said signal. A multifrequency signal is a signal combining two predetermined pure tones one, belonging to a high-frequency range the other to, a low-frequency range. The received signal is sampled at 8 KHz and digitally converted. The signal provided by the converter is simultaneously processed by two tone detectors. Each tone detector comprises : a bandpass filter covering the high- or low-frequency range and supplying the components (x, y) of the filtered signal in Cartesian coordinates; decimation means at the output of said filters; a converter converting the Cartesian coordinates (x, y) …