Chapter 4
Operating a marine VHF radio
Every make and model of marine VHF radio is different. Whilst there may be a certain family resemblance between different models from one manufacturer, or between competing products aimed at the same group of users, there is certainly no such thing as a “standard” control panel. There are, however, a number of standard controls:-
Power on
Volume
Squelch
Transmitter power
Channel selector
PTT switch
Dual watch/Tri watch/Scan
Dimmer
Power on
The power on/off switch connects the radio to its power supply, so until it has been switched on, the radio is useless.
In fixed mount radios, the power on/off switch is often a press-button, mounted on the front panel. In hand-held portables, it is often combined with the volume control.
Volume
The function of the volume control is exactly the same as that of its counterpart on a domestic radio or television: it makes the sound from the loudspeaker either louder or softer.
Some radios, particularly those with telephone-style handsets, have a “mute” facility, which switches the loudspeaker off altogether when the handset is removed from its cradle.
Squelch
The squelch control regulates the sensitivity of the receiver, so it affects the radio’s ability to receive incoming signals. It does not, however, affect the volume of the audio signal heard through the loudspeaker or handset.
Turning the squelch “up” reduces the sensitivity of the receiver and vice versa. When the squelch is turned right down, the receiver will detect a lot of very weak signals, including “static” and atmospheric noise, which will produce a sharp crackling, or frying sound through the loudspeaker. This is a very useful indicator of whether the volume control is set to about the right level, but no-one would put up with it as background noise for very long.
As the squelch control is gradually turned up, there will come a point at which the noise suddenly stops. This is the correct setting: the receiver has been desensitised sufficiently to eliminate unwanted signals, but should still be able to receive wanted signals.
Turning the squelch up further will desensitise the receiver still more, and runs the risk of losing weak signals.
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