What triggers a squelch circuit to activate?

The squelch circuit is a key component in communication systems, particularly in two-way radios. It is designed to suppress the audio output when the signal being received falls below a certain threshold, helping to eliminate background noise when no meaningful communication is present.

The trigger for a squelch circuit to activate is the presence of noise. When the receiver picks up a signal that is primarily noise, rather than a clear, intelligible voice or data signal, the squelch circuit activates. This means that it mutes the audio output to prevent the user from hearing the disruptive sounds that accompany a weak or noisy signal. The function of the squelch circuit is essential for ensuring that operators only hear audio when a clear and usable signal is received, thereby enhancing communication clarity.

In contrast, other options such as digital signals only, weak signal strength, and audio tones do not describe the correct conditions that specifically cause the squelch circuit to engage. While weak signal strength could lead to noise, it is the actual presence of noise that directly triggers the squelch.