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Q: Your VHF radio has low and high power settings, and although it works at low power perfectly, no one seems to hear you when the radio is set to high. Does the VHF need to be replaced?

A: VHF radio is the primary means of short distance communication between boats, marinas and port operations, and for summoning help in the event of an emergency. If they are to work as designed they must have two equally important things: a reliable power supply and a good antenna.

A VHF radio’s low and high power settings refer to its transmitting power. Low power is for very short-range communications, for instance when you are tied up in a harbor and need to call the yacht club launch. For this type of communication, the radiated power is normally about 1 watt. With the radio set to high the power output goes up to 25 watts, the maximum permitted from a marine VHF set. However, you will only get somewhere near this maximum if your antenna is correctly installed and wired to the radio.

The first thing I would check is the antenna connections on the back of the radio. Salt air is corrosive, and corrosion increases resistance and will prevent full power from reaching the antenna. The coaxial cable used between the radio and antenna comprises a thin central conductor insulated in a plastic sleeve, around which is a woven copper screen cable. There should be no contact between these parts. I have seen the wispy-looking screening distorted inside the plug and making contact with the central conductor. This should be avoided, since it will hamper the radio’s ability to transmit.

If you have doubts as to whether or not there is contact, I suggest purchasing a new plug from a marine supply store and remaking the end of the antenna cable. (Do this also if there are signs of corrosion.)

Next, check the cable connections on the underside of the antenna. These generally are molded into the base of the antenna or have a connector similar to that found at the back of the radio. If this fails to cure the problem, check the power supply to the radio. Transmitting on full power requires about 2.5 amps while the transmit button is pressed. If the battery is low and in need of recharging, it may lack sufficient reserves to supply this amount of power. Or the connections could be corroded. Check these and make sure they are clean and bright before lightly coating with petroleum jelly to ward off future corrosion.

If none of these suggestions remedies the situation, try the radio on a boat that you know has a working antenna and power supply before buying a replacement. At the very least you will be certain that you aren’t throwing away a perfectly good radio.