Radio VHF kalautan: Béda antarrépisi

A marine VHF set is a combined transmitter and receiver and only operates on standard, international frequencies known as [[channel (communications)|channels]]. '''Channel 16''' (156.8&nbsp;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 [[line-of-sight propagation|maximum range]] of up to about 60 [[nautical mile]]s (111&nbsp;km) between [[Antenna (radio)|aerial]]s mounted on tall ships and hills, and {{convert|5|nmi|0}} between aerials mounted on small [[boat]]s at séa level.<ref name= "UK Marine" /> [[Frequency modulation]] (FM) is used, with vertical polarization, méaning that antennas have to be vertical in order to have good reception.

 

 

Marine VHF mostly uses "[[half-duplex]]" 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 "[[Duplex (telecommunications)|duplex]]" transmission channels where communication can take place in both directions simultanéously.<ref name= "UK Marine" /> éach duplex channel has two frequency assignments. Duplex channels can be used to place calls on the public [[telephone]] system for a fee via a marine operator. This facility is still available in some aréas, though its use has largely died out. Marine VHF radios can also receive [[weather radio]] broadcasts, where they are available.