Furuno FM-2710 - Manual (Page 32)

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4-2. Communication Distance
The FM-2710 operates on the VHF band assigned for maritime mobile stations (156.025 to
163.275 MHz).
The VHF radio wave, unlike LF or HF, propagates like a light ray. Thus communication is only available with
another VHF antenna which is above the horizon. This is called line-of-sight.
Even if a clear line-of-sight condition exists, the radio wave is attenuated along the signal path. The
communication distance is limited also by transmitter power, antenna efficiency and receiver sensitivity.
The average communication range, using 25 W marine VHF, is 10 to 15 nm for ship-to-ship
and 20 to 30 nm for ship-to-shore.
Note that an obstruction in the signal path, such as a large ship, crane, building or mountain, can destroy
VHF communications even for a short distance.