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

							Antenna Handbook ____________________________ 
4-15
maximum gain at high take-off angles. In format D, the radiation
off the ends of the doublet also has maximum gain at high take-off
angles. This means that for short path-length circuits, which require
high take-off angles, a doublet antenna one-quarter wavelength
above ground produces almost omnidirectional coverage.
The vertical plots included for half-wave dipole antennas are given
for heights from 8 to 12 meters. The plot for 8 meters shows that for
3 and 9 MHz the antenna has high-angle radiation. At those fre-
quencies the antenna is close to ground (compared to a half-wave-
length). The pattern for 18 MHz shows the characteristic
bidirectional pattern since 8 meters is a half-wave at 18 MHz.
The half-wave dipole is a balanced resonant antenna (see fig. 4-10
on page 4-16). It produces its maximum gain for a very narrowABl2H=l2 H=CDl4H=l
4 H=
Figure 4-9. Illustrative Doublet Antenna Patterns. 
						

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MCRP 6-22D
range of frequencies, normally 2 percent above or below the design
frequency. Since frequency assignments are usually several mega-
hertz apart, it is necessary to construct a separate dipole for each fre-
quency assigned (see figs. 4-11 and 4-12 on page 4-17, and 4-13 on
page 4-19). If space and other resources are unavailable to erect sep-
arate dipoles, three or four dipoles can be combined to occupy the
space normally required for one. 
Each wire is a half-wavelength for an assigned frequency. The sepa-
rate dipoles are connected to the same center insulator, or preferably
a balun, and are fed by a single coaxial cable. When the antenna isFigure 4-10. Half-Wave Dipole Antenna. 
						

							Antenna Handbook ____________________________ 
4-17Figure 4-11. 8-Meter Half-Wave Dipole (Vertical Pattern).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 4-12. 10-Meter Half-Wave Dipole (Vertical Pattern).TAKE-OFF ANGLE
  3 MHz9 MHz10°10°20°20°30°30°40°40°50°50°60°60°70°70°80°80°90°151050-5-10-51015dBi 
						

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MCRP 6-22D
fed with an assigned frequency, the doublet cut for that frequency
will radiate the energy. Up to four separate dipoles can be combined
in this manner. When constructing this antenna, examine the indi-
vidual frequency assignments to determine if one frequency is three
times as large as another. If this relationship exists between two fre-
quencies, one dipole cut in length for the lower of the two frequen-
cies will work well for both frequencies.
The length of a half-wave dipole is calculated from the following
relationship:
The height of a half-wave dipole is figured using—
Use the right relationship for the right purpose. If the height rela-
tionship is used for the dipole length, the antenna will be too long
and will not work properly. Characteristics are—Dipole length=142 meters
or468 feet
Frequency in MHzFrequency in MHz
Height X/4=75 meters
or246 feet
Frequency in MHzFrequency in MHz
Height X/2
=150 meters
or492 feet
Frequency in MHzFrequency in MHz
Frequency range:± 2% of design frequency 
Polarization:Horizontal 
Power capability:1,000 watts
Radiation Pattern
Azimuthal (bearing):Bidirectional l l/2 high
basically omnidirectional at l l/4 high
Vertical (takeoff angle):See figures 4-11 and 4-12 on page
4-17, and 4-13 on page 4-19 
						

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Inverted Vee
The inverted vee, or drooping dipole, is similar to a dipole but uses
only a single center support (see fig. 4-14 on page 4-20). Like a
dipole, it is designed and cut for a specific frequency and has a
bandwidth of 2 percent above or below the design frequency.
Because of the inclined sides, the inverted vee antenna produces a
combination of horizontal and vertical radiation—vertical off the
ends and horizontal broadside to the antenna. All the construction
factors for a dipole also apply for the inverted vee. The inverted vee
has less gain than a dipole, but using only a single support could
make this antenna the preferred antenna in some tactical situations
(see fig. 4-15 on page 4-21). Figure 4-13. 12-Meter Half-Wave Dipole (Vertical Pattern).TAKE-OFF ANGLE  3 MHz9 MHz10°10°20°20°30°30°40°40°50°50°60°60°70°70°80°80°90°151050-5-10-51015dBi 
						

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MCRP 6-22D
Characteristics are—
.
Figure 4-14. Inverted Vee Antenna. Frequency range:± 2% of design frequency 
Polarization:Horizontal
Power capability:1,000 watts
Radiation pattern
Azimuthal (bearing):Basically omnidirectional with combi-
nation polarization
Vertical (take-off angle):See figure 4-15 
						

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4-21
Long Wire
A long wire antenna is one that is long compared to a wavelength
(see fig. 4-16 on page 4-22). A minimum length is one-half wave-
length. However, antennas that are at least several wavelengths long
are needed to obtain good gain and directional characteristics. Con-
structing long wire antennas is simple, and there are no critical
dimensions or adjustments. A long wire antenna will accept powerTAKE-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 4-15. Inverted Vee (Vertical Pattern). 
						

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MCRP 6-22D
and radiate it well on any frequency for which its overall length is
not less than one-half wavelength.
The gain and take-off angle of a long wire antenna depend on the
antenna’s length. The longer the antenna, the more gain, and the
lower the take-off angle. Gain has a simple relationship to length;
however, take-off angle is a bit more complicated. A long wire
antenna radiates a cone of energy around the tie wire, much like a
funnel with the antenna wire passing through the funnel opening.
The narrow part of the funnel would be the feed point, and the open
part would be toward the distant station. If the funnel were cut in
half, the resulting half cone would represent the pattern of the
antenna. As the antenna is lengthened, the cone of radiation (fun-
nel) moves closer and closer to the wire. Figure 4-17 shows patternFigure 4-16. Long Wire Antenna. 
						

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changes as the wire is lengthened. The patterns represent a view
from directly below the antenna.
In the three-wavelength pattern, for very low-angle radiation, posi-
tion the wire somewhat away from the direction of the distant sta-
tion so that the main lobe of radiation points at the receiving station.
If a higher take-off angle is required, point the wire directly at the
distant station. For take-off angles from 5 to 25 feet, the following
general off-axis angles will provide satisfactory radiation on toward
the distant station (see table 4-4).    
Table 4-4. Off-Axis Angle.
Wire Length (Feet)23456
Off-Axis Angle (Degrees)30201310101X2X3XFigure 4-17. Long Wire Radiation Patterns.
To make a long wire antenna directional, place a terminating device
at the distant station end of the antenna. The terminating device
should be a 600-ohm, noninductive resistor capable of absorbing at 
						

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MCRP 6-22D
least one-half of the transmitter power. Terminating resistors are
components of some radio sets but can also be fabricated locally
using supply system components (100-watt, 106-ohm resistor).
Constructing a long wire antenna requires only wire, support poles,
insulators, and a terminating resistor (if directionality is desired).
The only requirement is that the antenna be strung in as straight a
line as the situation permits. The antenna is only 15 to 20 feet above
ground, so tall support structures are not required. The antenna is
normally fed through a coupler that can match the antenna’s 600-
ohm impedance. Coaxial cable can be used if a 12 to 1 balun is
available to convert the coaxial cable 50-ohm impedance to the
required 600 ohms. Vertical radiation plots of this antenna are not
presented because of the great variation in the pattern as the length
changes. For take-off angles between 5 and 25 feet, use the off-axis
graph (table 4-4 on page 4-23) and the gain versus length graph
(table 4-5) to determine the proper antenna length. Characteristics
are—
Inverted L
The inverted L is a combination antenna made up of a vertical sec-
tion and a horizontal section (see fig. 4-18). It provides omnidirec-
tional radiation for ground wave propagation from the vertical
element and high-angle radiation from the horizontal element for
short-range sky wave propagation. The classic inverted L has a
quarter-wave vertical section and a half-wave horizontal sectionFrequency range:2 to 30 MHz
Polarization:Vertical
Power capability:1,000 watts
Radiation pattern
Azimuthal (bearing):Bidirectional with terminating resistor
Vertical (take-off angle):Depends on length