FRAC; Fracastoro; Fraccaro; Fraccaro, M. FRACDS; FRACGP; fracidin; FRACO; FRACOG; FRACP; FRACR; FRACS; fract-fract dos; Fractal; fractals; fraction; fraction collector; fraction of inspired oxygen; fractional; fractional dilation and curettage; fractional distillation; fractional excretion of sodium; fractional flow reserve; fractional injection; fractional oxyhemoglobin
In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a sufficiently strong desired input signal. carrier squelch is unlocked and will let any signal in. Selective calling locks out all signals except ones with the correct code. In non-critical uses, selective calling can also be used to hide the presence of interfering signals such as receiver-produced intermodulation.
External squelch logic takes the user-selected tone and the actual tone present and passes the voice signal if the selected tone and present tone match. I'll describe a method to detect CTCSS signals in this SDR environment using the modified Goertzel discrete Fourier transform (DFT) algorithm. We'll examine the algorithm itself and how it has been used by many others to detect dual-tone multifrequency (DTMF) signaling.