Icom AH-740 Instruction Manual - page 7
New2001
New2001
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2
INSTALLATIONS
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For best communications, position the antenna as high as
possible. The Figure 1 shows the preferred option selection.
The Figure 2 shows an antenna installation that uses the op-
tional AH-5NV, for best communications on the 30–300km
(18.6–186.5 miles) short ranges, and up to 1500 km (932
miles) medium ranges.
Figure 1
Figure 2
What is NVIS?
NVIS stands for Near Vertical Incidence Skywave.
The NVIS radio-wave propagation provides usable signals
between groundwave and skywave distances. (between 50
and 650 km; 30 and 400 miles) The radio waves from the
antenna travel upwards into the ionosphere, and then are
refracted back down in a circular area. The signals can be
received up to 650 km (400 miles) from the transmitting sta-
tion. Refraction fails if the frequency is too high. The signal
strength is reduced if the frequency is too low, because of
absorption.
precautions when the optional AH-5NV is in-
D
stalled on a vehicle
R
WARNING!
The NVIS antenna element can swing a lot
while driving. Therefore, we strongly recommend that you re-
move the NVIS antenna while driving. Otherwise the antenna
element may swing excessively and interfere with your driv-
ing.