What is the purpose of a squelch circuit in a receiver?

• A. To mute audio output when received signal is below a threshold, reducing noise and unwanted background hiss
• B. To boost audio output when a signal is strong
• C. To filter out high-frequency noise
• D. To convert between AM and FM modes

Answer: (A)

Squelch is about keeping the radio quiet when there’s nothing useful to hear. The circuit monitors the incoming signal and keeps the audio path muted until a real transmission breaks above a preset level. When the signal is below that threshold, you hear nothing or just silence, which removes the annoying background hiss that sits there when no station is transmitting. When a valid signal arrives, the squelch opens so the audio can be heard clearly.

This is why the option describing muting the audio below a threshold is the correct one. It isn’t about boosting loudness for strong signals—that would be gain control. It isn’t about removing high-frequency noise with a filter, which is a filtering function. It isn’t about changing modulation formats, which is a mode change.