8.3 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
the other vessel passes behind the curve of the Earth.
Therefore, the range will increase greatly the higher above sea
level the antenna is, as Fig 8.1 illustrates (assuming maximum
transmission power is used):
Instruction Manual
71
Part No. E04297
Therefore, the typical ship to ship range of a fixed VHF radio
such as the RS87 with a masthead antenna will be approxi-
mately 20 Km (12 miles). This will increase as height above
sea level increases, 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 8.1 - VHF transmission range
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