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Marine VHF Radio

Marine VHF radio in the frequency range 156 to 174 MHz, is mainly used for collision avoidence, summoning rescue services and communicating with harbours and marinas.

A marine VHF set is a combined transmitter and receiver of VHF transmissions on standard, international frequency bands known as "channels". Transmission power ranges between 1 and 25 Watts, giving a maximum range of 25 nautical miles between aerials mounted on tall ships and hills, and 3 nautical miles between aerials mounted on small boats at sea-level.

Sets can be portable or fixed. A portable set generally has the advantages of easily being carried to a lifeboatFor the 1944 movie, see Lifeboat (movie). A lifeboat is a boat designed to save lives of people in trouble at sea. There are two quite different usages. One usage is the lifeboats carried by passenger ships, the other the boats designed to be launched as in an emergency, having its own power source and being easily water-proofed. A fixed set generally has the advantages of a more reliable power source and a larger and more effective aerial and bigger display and buttons.

There are two types of equipment: "voice-only" and "digital selective calling".

Voice-only equipment is the traditional type, which:

• relies totally on the human voice for calling and communicating
• uses a number of " simplexTopology Geometry Geometry In geometry, a simplex is an n dimensional figure, being the convex hull of a set of n + 1) affinely independent points in some Euclidean space of dimension n or higher i. a set of points such that no m plane contains more than" transmission channels, which have a frequency band each, where communication can only take place in one direction at a time. A transmit button on the "set" determines whether it is operating as a transmitter or a receiver. Channel 16, the calling channel, this most important of these.
• uses a number of " duplexDuplex is the having of two principal elements or parts. A duplex home is the US name for a particular type of housing; see Semi-detached. A Duplex Lamp is a type of oil lamp. Telecommunications In telecommunications, duplex means "two-way" when referring" transmissions channels where communication can take place in both directions simultaneously. Each duplex channel has two frequency bands.
• uses a set of international "calling" procedures such as the " MaydayAlternative meanings: May Day, Mayday (music). Mayday is an emergency code word used internationally as a distress signal. Some people say that it was derived from the French M'aidez (help me). This is likely because most other urgency calls like Seelonce" distress call and the "Pan Pan" urgency call
• uses "pro-words" based on the English languageThe English language is a West Germanic language, originating from England. It is the third most common "first" language (native speakers), with around 402 million people in 2002. English has lingua franca status in many parts of the world, due to the mil 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
• uses this phonetic alphabet : Alpha, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Lima, Kilo, Mike, November, Oscar, Papa, Quebec, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu
• uses a phonetic numbering system based on the English languageThe English language is a West Germanic language, originating from England. It is the third most common "first" language (native speakers), with around 402 million people in 2002. English has lingua franca status in many parts of the world, due to the mil: Wun,Too,Tree,Fow-er,Fife,Six,Sev-en,Ait,Nin-er,Zero,Decimal

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 ditress 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