A marine VHF radio is a communications device installed on all large ships and on some motorized smaller crafts. Mainly used for collision avoidance, marine VHF’s are also used for summoning rescue services and communicating with harbors and marinas. Operating on VHF frequency, the device has a range between 156 to174 MHz. VHF (Very High Frequency), is the radio frequency range from 30 MHz to 300 MHz and is commonly used for FM radio and television broadcast. However, it’s mainly used for terrestrial navigation systems and aircraft communications.
With a combined transmitter and receiver, a marine VHF operates on standard international frequencies known as ‘channels’. For example, Channel 16 is the standard calling and emergency channel. The normal power of the transmission 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 smaller boats at sea-level. Standard marine VHF’s use ‘simplex’ transmissions; this means that communicators can only converse one at a time. Also available are ‘duplex’ transmission channels, where instead of a singular communication, a conversation can take place in both directions. These duplex channels also have two frequency functions; one can be used as a public telephone system. To select between the transmitter and the receiver, a transmit button is located on the set or on the microphone.
Marine radios also have the function to pick up NOAA Weather Radio broadcasts that are available on receive only channels such as wx1, wx2, and others. These radio systems can be fixed on ships or can be used as separate portable units. Fixed marine radios tend to be more reliable as they have a higher transmit power with bigger display buttons and cover a larger area with a more effective aerial. Portable radios are usually carried on lifeboats for emergency using their own power source. Other features include a distress button, a connection to a GPS receiver, and more. |
