Squelch

Squelch refers to a circuit function that suppresses the output of a receiver (typically a radio receiver) when the input signal strength falls below a certain threshold. The primary purpose of squelch is to eliminate or reduce unwanted background noise or static, making the receiver output silent until a valid signal is received.

The fundamental principle behind squelch is signal-to-noise ratio. When a radio receiver picks up weak signals, the signal is often accompanied by a significant amount of noise. This noise can be irritating and distracting to the listener. The squelch circuit analyzes the signal strength and, when it is below a pre-set threshold, mutes the audio output. When a signal strong enough to be reliably distinguished from the background noise is detected, the squelch circuit opens, allowing the signal to be heard.

There are several types of squelch circuits, including:

• Carrier Squelch: This is the most basic type, which simply monitors the presence or absence of a carrier signal at a specific frequency. If the carrier is below the set threshold, the squelch engages.
• Noise Squelch: This type of squelch monitors the noise floor of the received signal. When the noise level exceeds a certain threshold, the squelch is activated. This is more sophisticated than carrier squelch and less susceptible to false triggering by weak signals.
• Tone Squelch (CTCSS - Continuous Tone-Coded Squelch System or DCS - Digital Coded Squelch): These systems require a specific tone or digital code to be present in the received signal for the squelch to open. This allows multiple users to share the same frequency without hearing each other’s conversations unless the correct tone or code is present.

Squelch is commonly used in a wide range of radio communication systems, including two-way radios (walkie-talkies), CB radios, amateur radios, and public safety radio systems. It helps to improve the clarity and intelligibility of communications by eliminating unwanted noise and interference. It's a crucial feature for any receiver needing a quiet idle state and automatic activation upon a legitimate signal.