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.
The receiving radio may be programmed to only respond to signals transmitting the desired tone frequency. Digital Coded Squelch (DCS) is a digital form of CTCSS. A third type of squelch system, called Selective Calling (SelCall) is used in some business radios, but is not used in Ham radios. Note that none of these squelch systems are used in digital radios. CTCSS is also known by a number of other terms which are registered trademarks of individual manufacturers. Among them are Private Line (PL), owned by Motorola; Channel Guard (CG), owned by GE/Ericsson/Harris; and Quiet Tone (QT), owned by Kenwood.