What type of signals does CTCSS squelch rely on to operate?

CTCSS, or Continuous Tone-Coded Squelch System, operates by using low-frequency tones that are added to the voice signal to control the squelch function of a communication device, such as a radio transceiver. These tones, typically around 67 to 250.3 Hz, are sent continuously and are not part of the audio that carries the voice communication.

When a receiver is set to a specific CTCSS tone, it opens the squelch and allows the audio to pass through only when that designated tone is detected. This feature helps reduce noise and ensures that only relevant communications, associated with the correct tone, are heard. Thus, it enhances communication by filtering out unwanted signals.

The reliance on these specific tones, rather than speech signals, noise patterns, or data packets, is what makes CTCSS effective in providing clear and private communication in radio systems.