Marine VHF radio

Marine VHF radio is installed on all large ships and most motorized small craft. It is mainly used for collision avoidance, summoning rescue services and communicating with harbours and marinas, and operates in the VHF frequency range, between 156 to 174 MHz.

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 calling and emergency channel. Transmission power ranges between 1 and 25 watts, giving a maximum range of 25 nautical miles (46 km) between aerials mounted on tall ships and hills, and 3 nautical miles (6 km) between aerials mounted on small boats at sea-level.

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. There are also a number of "duplex" transmissions channels where communication can take place in both directions simultaneously. Each duplex channel has two frequency assignments. In some locations, the duplex channels can be used to place calls on the public telephone system for a fee via a marine operator. Marine VHF radios can also receive weatheradio broadcasts, where they are available, on receive-only channels wx1, wx2, etc.

Types of equipment

Sets can be fixed or portable. A fixed set generally has the advantages of a more reliable power source, higher transmit power, a larger and more effective aerial and a bigger display and buttons. A portable set can be carried to a lifeboat in an emergency, has its own power source and is more easily water-proofed.

Marine radios can be "voice-only" or can include "Digital Selective Calling".

Voice-only equipment is the traditional type, which relies totally on the human voice for calling and communicating

Digital Selective Calling equipment, a part of GMDSS, provides all the functionality of voice-only equipment and, additionally, allows several other features:

• a transmitter can call a receiver automatically using Digital Selective Calling on Channel 70, using a telephone-type number known as a Maritime Mobile Service Identity or MMSI
• a distress button, which automatically sends a digital distress signal indentifying the calling vessel and the nature of the emergency
• a connection to a GPS receiver allowing the digital distress message to contain the distressed vessel's position

The MMSI is a nine digit number identifying a VHF set or group of sets. The left hand digits of MMSI indicate the country and type of station. For eamples, here are MMSI prefixes of 4 types of station:

• Ship : 23 is the United Kingdom – e.g. a UK ship : 232003556
• Coast : 00 – e.g. Solent Coastguard : 002320011
• Group of stations : 0 – e.g. 023207823
• Portable DSC equipment : for UK 2359 - e.g. 235900498

Operating procedures

Proper operating procedures for marine radio include:

• Listening before transmitting
• Using Channel 16 only to establish communication (if necessary) and then switching to a different channel
• using a set of international "calling" procedures such as the "Mayday" distress call and the "Pan Pan" urgency 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, Romeo, Quebec, 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

External links

• US Coast Guard basic radio information for boaters (http://www.navcen.uscg.gov/marcomms/boater.htm)
• US Coast Guard marine channel listing (with frequencies) (http://www.navcen.uscg.gov/marcomms/vhf.htm)
• US FCC marine channel listing (by function) (http://wireless.fcc.gov/marine/vhfchanl.html)