Squelch

Squelch is a function in radio receivers and related equipment that mutes or reduces audio output when the received signal strength falls below a chosen threshold. The primary purpose is to suppress background noise or hiss when there is no meaningful transmission, making operation on shared channels more comfortable and practical.

Squelch can be implemented at different points in the signal chain. RF squelch decisions are based on the presence of a carrier at the radio frequency, while IF squelch uses the intermediate frequency after initial demodulation. More recent devices may use digital or soft squelch, which relies on signal processing to distinguish quiet noise from actual transmissions. A squelch control sets the threshold: when a signal exceeds the threshold, audio passes through; when it does not, the audio is muted. If the threshold is set too high, weak but valid signals may be suppressed; if too low, noise becomes audible on idle channels. Some systems feature automatic squelch control that adapts to changing conditions.

Squelch is widely used in two-way radios, scanners, citizen band radios, marine and aviation communication equipment, and amateur radio. It improves readability on crowded or noisy channels and facilitates fast channel scanning by preventing continuous noise. In practice, users must balance sensitivity with the desire to avoid noise, adjusting the squelch level to suit the operating environment. The term also appears in broader usage as a verb meaning to suppress or silence something.