Скачать или смотреть What is Squelch?

When there is no signal being received, a sensitive receiver can produce significant noise because automatic gain control disappears in the absence of any carrier. Receiver becomes more sensitive and amplifies any electrical noise present in the input. This especially more in FM receivers which produces a hissing noise when the squelch is kept open. The circuit used to quieten the noise while no signal is being received is known as squelch. Usually a volume control like mechanism is used to adjust the squelch level. While receiving weak signals of amateur radio satellites, squelch is intentionally kept open as the weak signals from satellites may not be enough to open the closed squelch. Powerful signals from satellites like the amateur radio on international space station may be able open squelch in high elevation passes when the satellite comes near overhead.