Extremely inaccessible areas may require establishing a site by
helicopter, should the tactical situation require it. Most tactical
communications equipment can be transported by helicopter and lowered
to the site.
d. Avoiding Obstructions.
The siting of the communications
antenna can be the difference between a good radio system and a poor
one.
Steel bridges, underpasses, power lines, and power generating
equipment cause weak and distorted signals. You obtain best results
when you position your antennas up high, and clear of hills,
buildings, dense woods, or other obstructions.
Figure 2-2
illustrates some desirable and undesirable antenna siting locations.
Note the direction of radiated energy.
e. Power Considerations. The reliability of your system depends
on the availability of a reliable electrical power source. Gasoline
or diesel engine powered generators are the primary sources of
electrical power for mobile equipment.
You must ensure that
maintenance
and
operating
personnel
rigorously
follow
proper
procedures to provide reliability for this equipment. You also must
ensure that the power is regulated to provide the proper voltages and
frequencies. Whenever possible, provide a backup or alternate power
source.
f. Polarization of Antennas.
Radio waves transmitted from a
vertical antenna are vertically polarized; those transmitted from a
horizontal antenna are horizontally polarized.
The performance of
your system depends largely on the polarization of your antenna. You
may want to use either type of polarization, depending on your
situation.
In all cases, the polarization for the transmitting
antenna and the receiving antenna must be the same.
Otherwise, the
loss of signal strength may prevent communications.
(1) Vertically polarized waves are less affected by aircraft
fly-over than are horizontal waves.
They are more efficient for
transmission over sea water at frequencies less than 100 MHz.
Ordinary LOS antennas less than 50 feet high work best when
vertically polarized.
At higher frequencies there is little
difference in performance.
(2) Horizontal antennas are less likely to pick up manmade
electrical interferences such as power lines or generators.
Such
interference is generally vertically polarized.
In dense forests,
horizontally polarized waves suffer less loss than vertical waves.
The standing wave effect of horizontal polarization is not as
pronounced as with vertical polarization.
2-6
SS0016
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