U.S. Marine Corps Antenna Mcrp 6 22D Operating Instructions

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MCRP 6-22D
Another problem could be misaligned directional antennas. If direc-
tional antennas are not correctly pointed at each other, communica-
tion is degraded. The directional antennas’ electrical characteristics
can change over several field deployments, especially if the antenna
is subjected to harsh use. These electrical characteristic changes can
cause the radiation pattern to change. Then, when the antenna is
physically pointed at the distant station,...

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In a dense forest, get the antenna tip above the treetops. This height
allows the radio signal to propagate in the clear space above the
trees. If it is impossible to raise the antenna above the trees, a hori-
zontally polarized antenna provides better communications throughFigure 8-1. Ridge Line Antenna Farm.DESIRED 
COMMUNICATIONSENEMYFigure 8-2. Antenna Sited on a Military Crest. 

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MCRP 6-22D
trees than a vertically polarized antenna. Figure 8-3 shows good,
fair, and poor antenna siting in dense trees.
A clearing in a forest improves propagation if the antenna is placed
so that the clearing is between the antenna and the distant station
(for a directional antenna). Place an omnidirectional antenna in the
center of a clearing, with the antenna as high as possible (fig. 8-4).
A communicator may have little choice in selecting a transmitter...

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Figure 8-4. Directional Antennas Sited in a Clearing.
Transmitting Antenna Site
Any site that has a horizon whose obstructions subtend vertical
angles of less than 2° from level in any of the directions of trans-
mission can be considered immediately as a satisfactory site from
the standpoint of radiation. As a simple rule, a satisfactory horizon
clearance exists when any obstruction subtends a vertical angle that
does not exceed one-half of the...

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MCRP 6-22D
For example, if the computed vertical beam angle for a one-hop cir-
cuit is 6° at an azimuth of 332°, and the horizon in this direction is a
range of mountains with a height of 8° as seen from the antenna
site, the performance of the circuit would be greatly compromised
by the obstruction of the mountains. It might be better to work this
circuit with two hops—a vertical beam of 20° could be used
instead, with adequate horizon clearance for the wave...

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Receiving Antenna Sites
Choosing a receiving antenna site is similar to choosing a transmit-
ting antenna site. The dominant angles of arrival of the incoming
waves at the site are determined mainly by the characteristics of the
transmitting antenna. Best results are obtained with complementary
transmitting and receiving antennas. If a horizon obstruction exists
at the optimum angle of wave arrival, a compromise, noncomple-
mentary antenna may be...

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MCRP 6-22D
ANTENNA FARM INTERNAL ARRANGEMENT
Frequency Band
The higher the frequency, the shorter the wavelength. The shorter
the wavelength, the more nearly LOS. The more nearly LOS, the
more critical is a clear LOS path for the signal.
Antenna Selection and Placement
Selection. The key to antenna selection rests with the answers to
the following three questions:
• To whom will you be transmitting?  Where will they be?
• What is the path between you and them?
•...

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nature of the interfering signal. Sometimes the interfering signals
combine with other frequencies in the system, including carrier-
sum and difference frequencies, to produce interference in a third
radio channel. The products may hold up automatic gain control
during critical fading periods, with serious effect on system noise.
Usually, noise in the base band channels is an end product.
Radio system interference may be introduced through antennas,...

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MCRP 6-22D
reradiate about one-half of the power they receive. If the receiving
antenna is within one wavelength of a transmitting antenna (it
makes absolutely no difference whether or not the receiving
antenna’s radio is tuned to the same frequency as the transmitting
radio), the receiving antenna will reradiate a portion of the signal
which may be out of phase with the original signal, altering the
transmitting antenna’s radiation pattern.
Direction of Desired...

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Multiply separations by 10 for each halving of frequency separation
(i.e., 10 for 5 percent; 100 for 2.5 percent).
For  a 5 percent separation—
For a 2.5 percent separation—
Separate antennas by a minimum of wavelength at the lowest fre-
quency at which they will operate to alleviate antenna coupling.
Separate antennas according to the desired direction of transmission
(i.e., don’t send the propagated wave through other antennas).
Polarization
The...