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5.2 Transmission Range
Because VHF signals travel in a straight line
and are not reflected 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 Figure 5.1 illustrates (assuming maxi-
mum transmission power is used):
Fig 5.1 - VHF transmission range
Therefore, the typical range of a handheld
radio such as this one used at sea level will be
approx. 8 km (5 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
handheld user increases to 13–16 km (8–10
miles).
