Marine VHF radio

Marine VHF radio is installed on all large ships and most motorized small craft. It is used for a wide variety of purposes, including summoning rescue services and communicating with harbours and marinas, and operates in the VHF frequency range, between 156 to 174 MHz. Although it is widely used for collision avoidance, its use for this purpose is contentious and is strongly discouraged by some countries, including the UK. ^[1]

A marine VHF set is a combined transmitter and receiver and only operates on standard, international frequencies known as channels. Channel 16 (156.8 MHz) is the international calling and distress channel. Channel 9 can also be used in some places as a secondary call and distress channel. Transmission power ranges between 1 and 25 watts, giving 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. ^[2] Frequency modulation is used.

Modern day marine VHF radios have a variety of features in addition to basic transmit and receive capabilities. All fixed mount marine VHF radios produced nowadays have some level of DSC calling capability. A number of the more expensive units are capable of acting as a hailer when connected to a hailer horn, can work with optional voice scramblers, and a few even have the ability to use a Bluetooth headset. A large number of unbiased independent reports on both fixed mount and handheld marine VHF radios can be seen at Marine Electronics Reviews

Marine VHF mostly uses "simplex" transmission, where communication can only take place in one direction at a time. A transmit button on the set or microphone determines whether it is operating as a transmitter or a receiver. The majority of channels, however, are set aside for "duplex" transmissions channels where communication can take place in both directions simultaneously ^[3]. Each duplex channel has two frequency assignments. This is mainly because, in the days before mobile phones and satcomms became widespread, the duplex channels could be used to place calls on the public telephone system for a fee via a marine operator. This facility is still available in some areas, though its use has largely died out. In US waters, Marine VHF radios can also receive weather radio broadcasts, where they are available, on receive-only channels wx1, wx2, etc.

Operating procedure

The accepted conventions for use of marine radio are collectively termed "proper operating procedure." These conventions include:

• Listening for 2 minutes before transmitting
• Using Channel 16 only to establish communication (if necessary) and then switch to a different channel
• using a set of international "calling" procedures such as the "Mayday" distress call, the "Pan-pan" urgency call and "Securité" navigational hazard call.
• using "pro-words" based on the English language such as Acknowledge, All after, All before, All stations, Confirm, Correct, Correction, In figures, In letters, Over, Out, Radio check, Read back, Received, Repeat, Say again, Spell, Standby, Station calling, This is, Wait, Word after, Word before, Wrong
• using the NATO phonetic alphabet: Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliet, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu
• using a phonetic numbering system based on the English language: Wun, Too, Tree, Fow-er, Fife, Six, Sev-en, Ait, Nin-er, Zero, Decimal

Marine VHF radio is sometimes illegally operated inland. Since enforcement is often the job of the local coast guard, enforcement away from the water is sometimes difficult.

Marine VHF Channels and Frequencies

Notes:

1: Some radios enable channels 3a, 61a, and 64a when configured for "USA mode" even though those channels are not listed for maritime use by the US Coast Guard or by the FCC. The frequencies in question appear to be used for land-mobile communication by police and fire departments in some US Cities.

2: Channel 22a is reserved for communication between the U.S. Coast Guard vessels and private vessels. The Coast Guard does not monitor 22a: Contact must first be established on 16.