Instruction Manual
45
E03912 Issue 2.0
5.3 Transmission range
Because VHF signals travel in a straight line and are not reflect-
ed back off the ionosphere as lower frequency signals are, the
range of VHF signals is limited to ‘line of sight’, beyond which
other vessels pass behind the curve of the Earth.
Therefore, the range will increase greatly the higher above sea
level the antenna is positioned, as Fig 5.1 illustrates (assuming
maximum transmission power is used):
The typical ship-to-ship range of a fixed VHF radio, such as the
RD68, with a masthead antenna will be approximately 20 km
(12 miles). This will increase as height above sea level increas-
es, or if the other radio user’s antenna is at a greater height –
note, that the range between the yacht with the antenna mounted
on a 9 m (30 ft) mast and the shore station increases to 46–53 km
(29–33 miles).
Fig 5.1 - VHF transmission range
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