Marine Antennas

Marine VHF radio is installed on all large ships and most seagoing small craft. It is used for a wide variety of purposes, including summoning rescue services and communicating with harbours, locks, bridges 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.

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. Frequency modulation is used, with vertical polarization, meaning that antennas have to be vertical in order to have good reception.

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.

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 . 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.

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 (often essentially a waterproof, VHF walkie-talkie in design) 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" (DSC).

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 the Global Maritime Distress Safety System (GMDSS), 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 send 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 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 example, here are MMSI prefixes of four station types:

• Ship : 232, 233, 234 or 235 are 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 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

Slightly adjusted regulations can apply for inland shipping, such as the Basle rules in Western Europe.

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.

3: UKSAR land based search & reacue teams have access to the simplexed versions of 24, 62, 63, 64, 85 for operational & training needs. These include Mountain Rescue teams in England, Wales & Scotland.

See also

• 2182 kHz
• Maritime mobile amateur radio
• AIS System
• Radio horizon

References

1. ^ UK Maritime and Coastguard Agency Marine Guidance Note MGN324
2. ^ UK Maritime and Coastguard Agency Marine Guidance Note MGN324
3. ^ UK Maritime and Coastguard Agency Marine Guidance Note MGN324

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