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.
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.
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. s
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:
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:
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.
| "A" frequency (MHz)|
Usually ship stations
| "B" frequency (MHz)|
Usually coast stations
|0||156.000||160.600||Private, coast guard Ⓐ|
|1||156.050||160.650|| Public Correspondence (Ship-to-Shore Duplex) |
|3||156.150||160.750||Ⓐ Illegal for public use1|| Public|
|4||156.200||160.800|| Ship-to-ship/shore, commercial and safety|
BC and East Coasts Ⓐ
|9||156.450||161.050||Ship-to-ship Ⓐ||Calling Ⓐ, commercial and non-commercial.|
|13||156.650||161.250||Ship-to-ship Ⓐ||Bridge-to-Bridge safety Ⓐ: Vessels > 20m must maintain watch, Tx limited to 1 watt.|
USA: All vessels equipped with VHF must maintain watch.
|21||157.050||161.650||Ⓐ U.S. Coast Guard Only|
|22||157.100||161.700||Ⓐ U.S. Coast Guard—public working channel2|
|23||157.150||161.750||Ⓐ U.S. Coast Guard Only|
|61||156.075||160.675||Ⓐ Illegal for public use1|
|64||156.225||160.825||Ⓐ Illegal for public use1|
|69||156.475||161.075||Non-commercial Ⓐ||Australian Navy|
|70||156.525||161.125||Digital Selective Calling Ⓐ|
|72||156.625||161.225||Non-commercial ship-to-ship Ⓐ|
|81||157.075||161.675||Ⓐ U.S. Government Use Only|
|82||157.125||161.725||Ⓐ U.S. Government Use Only|
|83||157.175||161.775||Ⓐ U.S. Coast Guard Use Only|
|87||157.375||161.975||Automatic Identification System Ⓑ|
|88||157.425||162.025||Automatic Identification System Ⓑ|
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.
1. Comprehensive AMC of GP-328 Walkie-Talkie/ Portable Motorola VHF Radio Sets (115 Nos.) of Rajmahal Area. 2. Comprehensive AMC of GP-300 Walkie-talkie/ Portable Motorola VHF Radio Sets (35 Nos.) of R
Nov 05, 2013; Tenders are invited for 1. Comprehensive AMC of GP-328 Walkie-talkie/ Portable Motorola VHF Radio Sets (115 Nos.) of Rajmahal...