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

							Antenna Handbook ______________________________ 
4-5
After selecting the antenna, determine how to feed the power from
the radio to the antenna (fig. 4-1). Most tactical antennas are fed
with coaxial cable (RG-213). Coaxial cable is a reasonable compro-
mise of efficiency, convenience, and durability. Issued antennas
include the necessary connectors for coaxial cable or for direct con-
nection to the radio. 
Figure 4-1. Antenna Feed Lines.
Problems may arise in connecting field expedient antennas. The
horizontal half-wave dipole uses a balanced transmission line
(open-wire). Coaxial cable can be used, but it may cause unwanted
RF current. 
A balun prevents unwanted RF current flow, which causes a radio
to be hot and shock the operator. Install the balun at the dipole feed
point (center) to prevent unwanted RF current flow on the coaxial
cable. If a balun is unavailable, use the coaxial cable that feeds thePLASTIC SHIELDING
BRAIDINSULATIONINSULATING SPACERSWIRECENTER CONDUCTOR 
						

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MCRP 6-22D
antenna as a choke (see fig. 4-2). Connect the cable’s center wire to
one leg of the dipole and the cable braid to the other antenna leg.
Form the coaxial cable into a 6-inch coil (consisting of ten turns),
and tape it to the antenna under the insulator for support. 
  DETERMINING ANTENNA GAIN
Determine antenna gain at a specific take-off angle from the vertical
radiation pattern. Figure 4-3 shows the vertical antenna pattern for
the 32-foot vertical whip. The numbers along the outer ring (90°,
80°, 70°) represent the angle above the Earth; 90° would be straight
up, and 0° would be along the ground. Along the bottom of the pat-
tern are numbers from -10 (at the center) to +15 (at the edges).
These numbers represent the gain in decibels over an isotropic radi-
ator (dBi). 
To find the antenna gain at a particular frequency and take-off
angle, locate the desired take-off angle on the plot. Follow that line
toward the center of the plot to the pattern of the desired frequency.
Drop down and read the gain from the bottom scale. If the gain of a
32-foot vertical whip at 9 MHz and 20° take-off angle is desired,
locate 20° along the outer scale. Follow this line to the 9-MHz6” COIL TAPED TO INSULATOR
COAX
TO TRANSMITTERFigure 4-2.  Coax RF Current Choke. 
						

							Antenna Handbook ______________________________ 
4-7
pattern line. Move down to the bottom scale. The gain is a little less
than 2.5 dBi (the line between 0 and 5 dBi). The gain of the 32-foot
vertical whip at 9 MHz and 20° is 2 dBi.
Once the antenna’s overall characteristics are determined, use the
antenna selection matrix (table 4-3 on page 4-8) to find the specific
antenna for a circuit. If the proposed circuit requires a short-range,
omnidirectional, wideband antenna, the selection matrix shows that
the only antenna that meets all the criteria is the AS-2259/GR. 
If the circuit requires a medium-range directional antenna, several
antennas could be used (e.g., long wire, sloping vee, or vertical half-
rhombic). The antenna choice depends on available installation
space, available components, and required highest gain take-off
angle. For a required take-off angle of 25° at a frequency of 9 MHz,TAKE-OFF ANGLE  3 MHz9 MHz10°10°20°20°30°30°40°40°50°50°60°60°70°70°80°80°90°151050-5-10-51015dBiFigure 4-3. 32-Foot Vertical Whip, Vertical Pattern. 
						

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MCRP 6-22D
the 100-foot vertical half-rhombic antenna is the best choice because
it provides the highest gain at the required take-off angle.  
ANTENNA TYPES
The AS-2259/GR, vertical whip, half-wave dipole, inverted vee,
long wire, inverted L, sloping vee, sloping wire, and vertical half-
rhombic antennas are described and illustrated.Table 4-3. Antenna Selection Matrix.
UseDirectivityPolar-
izationBand-
width
Sky WaveGround Wave
Short (500 Miles)
Medium (500 to 1200 Miles)
Long (1200 Miles)
Omnidirectional
Bidirectional
Directional
Horizontal
Vertical
Wide
NarrowAS-2259/GRXXX
Vertical WhipXXXX
Half-Wave DipoleXXXXX
Inverted VeeXXXXXXX
Long WireXXXXXXX
Inverted LXXXXXXXX
Sloping VeeXXXXXX
Sloping WireXXXXXXX
Vertical Half-RhombicXXXXXX 
						

							Antenna Handbook ______________________________ 
4-9
AS-2259/GR
The AS-2259/GR antenna (fig. 4-4)  provides NVIS propagation for
short-range radio circuits. It consists of two crossed sloping dipoles
positioned at right angles to each other and is supported at the center
by a 15-foot mast.  In use, the dipole’s components provide guying
support for the mast. Characteristics are—
Frequency range:2 to 30 MHz
Polarization:Horizontal and vertical simultaneously
Power capability:1,000 watts
Radiation pattern
Azimuthal (bearing):Omnidirectional
Vertical (take-off angle):See figure 4-5 on page 4-10Figure 4-4. AS-2259/GR. 
						

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MCRP 6-22D
 
Figure 4-5. AS-2259 Vertical Radiation Pattern.
Vertical Whip
The vertical whip is a component of all Marine Corps radio sets
(see fig. 4-6). It is available and easy to use on almost all radio cir-
cuits; however, it is probably the worst antenna to use on sky wave
circuits. Unless the radio circuit involves omnidirectional ground
wave propagation, any other antenna would provide better commu-
nications. For example, vertical whips are often used for long-range
point-to-point circuits with marginal success. Since the circuit is
point-to-point, there is no need to radiate energy in all directions.
Radiation in directions other than at the distant station is wasted and
serves no useful purpose. Concentrating the omnidirectional radia-
tion at the distant station produces a better received signal and
reduces interference around the transmitting antenna. Concentrate
radiation in a single direction with a directional antenna. Figures10°
10° 20°
20° 30°30° 40°40° 50°50° 60°60° 70°70° 80°80° 90°  3 MHz9 MHzTAKE-OFF ANGLE151050-5-10-51015dBi 
						

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4-11
4-7 on page 4-12, 4-8 on page 4-13, and 4-3 on page 4-7 illustrate
various vertical whip antenna patterns.
Characteristics are—
Frequency range:2 to 30 MHz
Polarization:Vertical
Power capability:Matched to specific radio
Radiation pattern
Azimuthal (bearing):Omnidirectional
Vertical (take-off angle):See figures 4-7 on page 4-12, 4-8 on 
page 4-13, and 4-3 on page 4-7
Figure 4-6. Vertical Whip with Reflector.
If a vertical whip must be used, there are several techniques to
improve the antenna radiation. If the antenna is mounted directly to
the radio, ground the radio. If the antenna is remoted from the radio
ground the antenna base plate. A 6-foot ground rod is preferable for
both. Ground radials (wires spread out like wheel spokes with the
antenna at the center) may improve the antenna radiation. Connect
these radials to the ground rod directly beneath the antenna. 
						

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MCRP 6-22D
A ground radial system can be constructed easily from field tele-
phone wire (WDl/TT) and can be kept with the radio. Cut the field
wire into twenty 45-foot lengths, and remove 6 inches of insulation
from one end. Using twine or a clamp, bundle together the uninsu-
lated (bare) ends. Attach a 2-foot length of thick wire to the bare
ends so that the thick wire extends about one foot beyond the wire
bundle. Solder the wire bundle to ensure good electrical contact. In
use, the thick wire extending from the bundle connects the radials to
a ground rod. The radials are then spread out like wheel spokes with
the vertical whip at the center. Radio operators should experiment
with different radial systems to determine which one provides the
best connectivity.  
A reflector placed approximately one-quarter wavelength behind a
vertical whip may also improve the whip’s performance. A reflector10°
10° 20°
20° 30°30° 40°40° 50°50° 60°60° 70°70° 80°80° 90°TAKE-OFF ANGLE151050-5-10-51015dBi9 MHzFigure 4-7. 10-Foot Vertical Whip (Vertical Pattern). 
						

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4-13
is a vertical wire, metallic pole, or another whip that is insulated
from the ground. It is placed so that the reflector, the whip, and the
distant station are on a straight line. The reflector will reflect radio
energy striking it and cause the energy to travel toward the distant
station, increasing the total energy radiated in the desired direction.
To work properly, the reflector must be longer than the whip. If the
reflector is shorter, it will act as a director, directing the radio signal
away from the distant station. A reflector is longer and is placed
behind the whip; a director is shorter and is placed between the
whip and the distant station. Adjust the position of the reflector
while listening to the distant station until the strongest signal is
received.TAKE-OFF ANGLEdBi10°10°20°20°30°30°40°40°50°50°60°60°70°70°80°80°90°151050-5-10-510159 MHzFigure 4-8. 15-Foot Vertical Whip (Vertical Pattern). 
						

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MCRP 6-22D
The length of a vertical whip antenna is calculated from the follow-
ing formula:
For WD-l/TT
Half-Wave Dipole
The horizontal half-wave dipole (doublet) antenna  is used on short-
and medium-length sky wave paths (up to approximately 1,200
miles). Since it is relatively easy to design and construct, the dou-
blet is the most commonly used field expedient wire antenna. It is a
very versatile antenna; by adjusting the antenna’s height above
ground, the maximum gain can vary from medium take-off angles
(for medium path-length circuits) to high take-off angles (for short
path-length circuits). When the antenna is constructed for medium
take-off angle gain (a height of approximately one-half wave-
length), the doublet is a bidirectional antenna (i.e., the maximum
gain is at right angles to the wire). This is the broadside pattern nor-
mally associated with a half-wave dipole antenna. Format A in fig-
ure 4-9 shows this pattern in polar plot format.
Format B shows the radiation off the ends of the wire. It is easily
seen by comparing with format A that for maximum gain, a doublet
one-half wavelength above ground should be constructed so that the
side of the antenna points in the direction of the distant station. If
the antenna is lowered to only one-quarter wavelength above
ground, format C results. This lower antenna height producesLength in feet
=  234
Frequency in MHz
Length in feet
= 225.50
Frequency in MHz