The level of incoming radio signals is set by the Squelch (Mute) control, either by using a rotating knob (clockwise or anti-clockwise), or a push-button (^ and v) control, which affects the sensitivity of the receiver .

Squelch can, therefore, affect the radio’s ability to receive incoming signals, though without affecting the volume of the audio signal heard through the loudspeaker or handset earphone.

Turning the squelch up reduces the sensitivity of the receiver and vice versa. With the squelch turned down the receiver will detect lots of very weak signals, including static and atmospheric noise, which produces crackling or hissing noise through the loudspeaker or handset earphone when no voice signal is being received. This is a very useful indication of whether the volume control is set to the optimum level in order to receive information clearly.

However, one could not put up with this background noise for very long, so by adjusting the squelch control up there will come a point at which the background noise hiss suddenly stops. This is the correct setting for the squelch control, that is, the receiver sensitivity has been reduced sufficiently to eliminate unwanted signals and noise, but will still be able to receive 'wanted' signals. Turning the squelch up further will reduce the sensitivity of the receiver still more and can result in the loss of weak wanted signals.

	Rotating squelch control	Push- button squelch control
To turn the squelch up	rotate control clockwise	push button arrow ^
To turn the squelch down	rotate control anti-clockwise	push button arrow v

Practice on MF/HF radio simulator

After switching the MF/HF radio ON, it is first necessary to set the receiver squelch to an appropriate level to eliminate receiver noise and optimize receiver sensitivity.