Marine VHF radio is installed on all large ships and most seagoing small craft. It is also used, with slightly different regulation, on rivers and lakes. It is used for a wide variety of purposes, including summoning rescue services and communicating with harbours, marinas, and other vessels. It operates in the very high frequency (VHF) range, between 156 and 162.025 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 international calling 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; 6 mi) between aerials mounted on small boats at sea level. Frequency modulation (FM) is used, with vertical polarization, meaning that antennas have to be vertical in order to have good reception.
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 as “semi-duplex” transmission channels where communication can take place in both directions simultaneously. Each semi-duplex channel has two frequency assignments. Marine VHF radios can also receive weather radio broadcasts, where they are available.
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 (often essentially a waterproof, VHF walkie-talkie in design) can be carried on a lifeboat in an emergency, has its own power source and is water-proof.
Digital Selective Calling equipment, provides all the functionality of voice-only equipment and, additionally, allows several other features:
- a transmitter can automatically call a receiver equipped with Digital Selective Calling, using a telephone-type number known as a Maritime Mobile Service Identity or MMSI. The DSC information is sent on the reserved Channel 70. When the receiver picks up the call, his active channel is automatically switched to the transmitter’s channel and normal voice communication can proceed.
- a distress button, which automatically sends a digital distress signal identifying 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 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 (local language is used for some of these, when talking to local stations)
- 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
Although all entrants in the Great Pacific Race will have to complete a VHF radio course there’s no harm in getting ahead of everyone else and learning how to use a VHF radio now.
This great online course teaches all the basics about what a VHF / DSC radio is and how to use VHF / DSC radios. What a great way to remind yourself of the radio basics.