Squelch operation in broadcast/communications receivers What does a typical squelch circuit do under no-signal (no carrier) conditions to avoid loudspeaker noise?

Introduction / Context:
Squelch (muting) improves user experience by silencing the loud hiss or noise when a receiver is not tuned to a station or when the incoming carrier falls below a threshold. It is widely used in FM communications receivers and in AM/FM sets to avoid irritating audio between stations.

Given Data / Assumptions:

• Standard superheterodyne receiver with AGC/AVC.
• No valid carrier or the carrier is below the squelch threshold.
• We are interested in the typical action performed by the squelch circuit.

Concept / Approach:

Most squelch systems monitor signal metrics (noise level, carrier presence, or recovered DC from discriminator) and then control the audio path. When no carrier is detected, they mute the audio stage so that only silence is heard. This avoids blasting noise while tuning or during weak-signal fades.

Step-by-Step Solution:

Verification / Alternative check:

Service manuals often show the squelch voltage muting the audio path or disabling AF preamplifiers. IF muting exists in some designs but typical squelch silences the AF chain rather than completely shutting down IF gain.

Why Other Options Are Wrong:

Cutting off IF stages per AGC extremes is not standard squelch action; “eliminating RF interference” is too vague; boosting LO power is unrelated and undesirable.

Common Pitfalls:

Confusing AGC (automatic gain control) with squelch; AGC adapts gain to signal strength, while squelch mutes audio to hide noise.

Final Answer:

Cuts off an audio amplifier when the carrier is absent