VHF Radio Coverage and Range

Fixed-mount radios are limited to 25 watts of transmit power while Handhelds VHF radios have a maximum output of six watts.

Transmission power ranges between 1 and 25 watts with a maximum range of up to about 60 nautical miles (111 km) between aerials mounted on tall ships and hills, and 5 nautical miles (9 km) between aerials mounted on small boats at sea-level. The antennas should be vertical in order to have good reception.

How does a repeater work?

A repeater station is a stand-alone receiver and transmitter. The receiver will receive transmissions on the repeater channel frequency and then retransmits this through the transmitter. The nominal range of every repeater is 80km, but this will vary from repeater to repeater and should also be noted that as VHF is essentially “line of sight”, some areas of coastline might be in a shadow zone.

Repeater channels known as “duplex” use different frequencies for transmitting and receiving.  For “simplex” channels, such as Channel 16, the transmitting and receiving frequencies are the same.

Repeaters were originally for vessel to vessel communications, but it soon became apparent that all repeaters could be monitored from shore stations, when several link radio stations were fitted.

How do I access a repeater?

The closest repeater station to your vessel should be the appropriate channel number selected on your VHF radio. It is important to check that your unit is set to “international” as this ensures the duplex frequency repeater channels are used. And then, it is a matter of calling the desired receiving station, either another vessel or a coast radio station.

Read about How to make an Emergency Call...