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

							Antenna Handbook ____________________________ 
4-35
Characteristics are—
Figure 4-27. 100-Foot Sloping Wire (Vertical Pattern). Frequency range:Depends on wire length/configura-
tion
Polarization:Vertical
Power capability:Determined by terminating resistor
Radiation pattern
Azimuthal (bearing):Bidirectional for unterminated
Directional for terminated
Vertical (take-off angle):See figure 4-27 and figures 4-28 and
4-29 on page 4-36TAKE-OFF ANGLE10°10°20°
20° 30°30° 40°40° 50°50° 60°60° 70°70° 80°80° 90°151050-5-10-51015dBi  3 MHz9 MHz 
						

							4-36 ____________________________________ 
MCRP 6-22DTAKE-OFF ANGLE10°10°20°
20° 30°30° 40°40° 50°50° 60°60° 70°70° 80°80° 90°151050-5-10-51015dBi  3 MHz9 MHzFigure 4-28. 250-Foot Sloping Wire (Vertical Pattern).TAKE-OFF ANGLE10°10°20°
20° 30°30° 40°40° 50°50° 60°60° 70°70° 80°80° 90°151050-5-10-51015dBi
  3 MHz9 MHzFigure 4-29. 234-Foot Sloping Wire (Vertical Pattern). 
						

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4-37
Vertical Half-Rhombic
The vertical half-rhombic antenna is a version of the long wire
antenna that uses a single center support (see fig. 4-30).  Easily con-
structed, this antenna has a narrow width (as wide as the center sup-
port guys), which allows several to be installed in a relatively
narrow area. The vertical half-rhombic antenna radiates a medium-
to low-angle signal, making it a good choice for medium- to long-
range sky wave circuits. Normally, the 500-foot version is the max-
imum length of antenna that most tactical situations will allow;
however, the vertical radiation pattern for a 1,000-foot version is
included, so that if the opportunity exists, the antenna can be used
for excellent results.
Figure 4-30. Vertical Half-Rhombic Antenna. 
						

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MCRP 6-22D
The vertical half-rhombic uses a single wire feed either through a
coupler or a balun (12 to 1). One of the two terminals of the coupler
or balun is attached to the antenna, while the other terminal is
grounded. Like other terminated antennas, the terminating resistor
(600 ohms) should be able to handle one-half of the transmitter’s
power output. Terminators can be procured or fabricated locally
(100-watt, 106-ohm resistor).
The orientation of this antenna depends on the frequency bands
being worked. Below 12 MHz, point the terminated end of the
antenna at the distant station; above 12 MHz, aim the antenna 10
feet to either side of the distant station. Figures 4-31 and 4-32 illus-
trate the vertical patterns for various vertical half-rhombic antennas.
Characteristics are—
Frequency range:2 to 30 MHz
Polarization:Vertical
Power capability:Determined by terminating resis-
tor
Radiation pattern
Azimuthal (bearing):Directional
Vertical (take-off angle):See Figures 4-31 and 4-32 
						

							Antenna Handbook ____________________________ 
4-39TAKE-OFF ANGLE10°10°20°
20° 30°30° 40°40° 50°50° 60°60° 70°70° 80°80° 90°151050-5-10-51015dBi  3 MHz9 MHzFigure 4-31. 50-Foot Vertical Half-Rhombic (Vertical Pattern),
500 Feet Long.TAKE-OFF ANGLE10°10°20°
20° 30°30° 40°40° 50°50° 60°60° 70°70° 80°80° 90°151050-5-10-51015dBi
  3 MHz9 MHzFigure 4-32. 50-Foot Vertical Half-Rhombic (Vertical Pattern),
1,000 Feet Long. 
						

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MCRP 6-22D
HF NVIS COMMUNICATIONS
NVIS propagation is simply sky wave propagation that uses anten-
nas with high-angle radiation and low operating frequencies. Just as
the proper selection of antennas can increase the reliability of a
long- range circuit, short-range communications also require proper
antenna selection. NVIS propagation is one more weapon in the
communicator’s arsenal.
To communicate over the horizon to an amphibious ship on the
move, or to a station 100 to 300 kilometers away, the operators
should use NVIS propagation. The ship’s low take-off angle
antenna is designed for medium and long-range communications.
When the ship’s antenna is used, a skip zone is formed. This skip
zone is the area between the maximum ground wave distance and
the shortest sky wave distance where no communications are possi-
ble. Depending on operating frequencies, antennas, and propagation
conditions, this skip zone can start at roughly 20 to 30 kilometers
and extend out to several hundred kilometers, preventing communi-
cations with the desired station.
NVIS propagation uses high take-off angle (60° to 90°) antennas to
radiate the signal almost straight up. The signal is then reflected
from the ionosphere and returns to Earth in a circular pattern all
around the transmitter. Because of the near-vertical radiation angle,
there is no skip zone. Communications are continuous out to several
hundred kilometers from the transmitter. The nearly vertical angle
of radiation also means that lower frequencies must be used. Gener-
ally, NVIS propagation uses frequencies up to 8 MHz.
The steep up and down propagation of the signal gives the operator
the ability to communicate over nearby ridge lines, mountains, and
dense vegetation. A valley location may give the operator terrain
shielding from hostile intercept and also protect the circuit from 
						

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4-41
ground wave and long-range sky wave interference. Antennas used
for NVIS propagation need good high take-off angle radiation with
very little ground wave radiation (see fig. 4-33). 
Using the HF antenna selection matrix (table 4-4 on page 4-8), the
AS-2259/GR and half-wave dipole are the only antennas listed that
meet the requirements of NVIS propagation. While the inverted vee
and inverted L antennas have high-angle radiation, they also can
have strong ground wave radiation that could interfere with the
close-in NVIS communications. These antennas could be used if
terrain shielding prevented the ground wave signal from propagat-
ing to the distant station.
Figure 4-33.  NVIS Propagation. 
						

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MCRP 6-22D
The dipole antenna pattern is illustrated in figures 4-11 and 4-12 on
page 4-17 and figure 4-13 on page 4-19. The patterns for 3 and 9
MHz show that large amounts of energy are directed up in the 60°
to 90° range. Also, the pattern is the same on both sides of the 90°
line. This means that a low dipole would be a good antenna for
NVIS propagation. The pattern at 18 MHz is not important because
NVIS propagation normally does not use frequencies much above 8
MHz. Set up dipoles on whatever supports are available. Ensure
that the height is below a quarter-wavelength, which at 8 MHz is
about 30 feet.
Mobile CPs do not always have time to set up a dipole antenna or
an AS-2259/GR.  Several options are possible. If a Marine is in an
MRC-138 vehicle, then use a tilt whip adapter and the 16-foot whip
antenna to try to obtain high-angle radiation (fig. 4-34). Tilt the
antenna at least 30°. Another option is disconnecting the whip
antenna and connecting a 32-foot wire to the antenna base. Run the
wire parallel to the ground, and stake it at the distant end the same
height above the ground as the radio end. Insulate the staked end
from the ground to prevent radio damage (fig 4-35). Figure 4-34. AN/MRC-138 with NVIS Antenna. 
						

							Antenna Handbook ____________________________ 
4-43  WARNINGTHE WIRE MUST BE PROTECTED SO THAT MARINES DO
NOT WALK INTO IT. IT CARRIES ENOUGH RF ENERGY DUR-ING TRANSMISSION TO CAUSE SEVERE INJURIES.
When using a manpack radio like the AN\PRC-104, the whole radio
can be rotated so that the 8-foot antenna is tilted at least 30°.
Because of the antenna’s flexibility, it will need support on the far
end. This support must be a good insulator. Ensure that Marines
keep clear of the antenna. Characteristics are—
Frequency range:2 to 30 MHz
Polarization:Vertical or horizontal
Power capability:100 to 400 Watts
Radiation pattern
Azimuthal (bearing):Basically omnidirectional
Vertical (take-off angle):Minimizes skip zone using 90°,
40°, and 20° take-off angleFigure 4-35. AN/MRC-138 with Stationary NVIS Antenna. 
(reverse blank) 
						

							Chapter 5
VHF and UHF Antenna Selection
FREQUENCIES
The VHF portion of the radio spectrum extends from 30 to 300
MHz. The UHF range reaches from 300 to 3,000 MHz (3 GHz).
Both frequency ranges are extremely useful for short-range (less
than 50 km) communications. This includes point-to-point, mobile,
air-to-ground, and general purpose communications. A wavelength
at these frequency ranges is considerably shorter than those in the
HF range, and simple antennas are much smaller. 
Because the VHF and UHF antennas are small, it is possible to use
multiple radiating elements to form arrays, which provide a consid-
erable gain in a given direction or directions. An array is an
arrangement of antenna elements, usually dipoles, used to control
the direction in which most of the antenna’s power is radiated.
Generally, many more types of antennas are available and useful in
the VHF and UHF range than at HF. Several of these types will be
discussed in this chapter since they are useful for various field
applications.
Within the VHF and UHF portion of the spectrum, there are several
subfrequency bands for specific uses. The 118 to 136 MHz range is
generally reserved on a worldwide basis for air-to-ground commu-
nications and is known as the VHF aircraft band. The 225 to 400
MHz range is also allocated for air-to-ground use and is known as
the UHF aircraft band. The 148 to 174 MHz and 450 to 470 MHz