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The use of digital squelch on a channel that has existing tone squelch users precludes the use of the 131.8 and 136.5 Hz tones as the digital bit rate is 134.4 bits per second and the decoders set to those two tones will sense an intermittent signal (referred to in the two-way radio field as "falsing" the decoder). [2]
In telecommunications, squelch is a circuit function that acts to suppress the audio (or video) output of a receiver in the absence of a strong input signal. [1] Essentially, squelch is a specialized type of noise gate designed to suppress weak signals.
CTCSS (Continuous Tone-Coded Squelch System) superimposes any one of about 50 continuous audio tones on the transmitted signal, ranging from 67 to 254 Hz. [1] At any time when the transmitter is on, the tone is encoded on the signal.
The crudest and oldest of these is called CTCSS, or Continuous Tone-Controlled Squelch System. This consists of superimposing a precise very low frequency tone on the audio signal. Only the receiver tuned to this specific tone turns the signal into audio: this receiver shuts off the audio when the tone is not present or is a different frequency.
Selcall (selective calling) is a type of squelch protocol used in radio communications systems, in which transmissions include a brief burst of sequential audio tones. . Receivers that are set to respond to the transmitted tone sequence will open their squelch, while others will remain
FRS radios frequently have provisions for using sub-audible tone squelch (CTCSS and DCS) codes, filtering out unwanted chatter from other users on the same frequency. Although these codes are sometimes called "privacy codes" or "private line codes" (PL codes), they offer no protection from eavesdropping and are intended only to help reduce ...
The complexities in communications system design often introduce delay in the time it takes to turn on the various components comprising the system. Transmitters take time to come up to full power output, tone squelch decoding equipment requires time to open receivers and receiver voting systems take time to select the best receiver.
Systems transmitted a continuous tone (at 3051.9 Hz by default), called Busy Tone. A low-pass filter eliminated most of the tone from speaker audio. The tone was present through the transmission, but cut off just before the repeater dropped in order to eliminate squelch tail.