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

Antenna Handbook ____________________________ 
2-15
transmitter power will dissipate as heat into the ground rather than
radiated as intended. Therefore, it is essential to provide as good a
ground or artificial ground (counterpoise) connection as possible
when using a vertical whip or monopole.
The amount of power an antenna radiates depends on the amount of
current which flows in it. Maximum power is radiated when there is
maximum current flowing. Maximum current flows when the
impedance is...

2-16 ____________________________________ 
MCRP 6-22D
In the radio communication process, intelligence changes from
speech or writing into a low frequency signal that is used to modu-
late, or cause change, in a much higher frequency radio signal.
When transmitted by an antenna, these radio signals carry the intel-
ligence to the receiving antenna, where it is picked up and recon-
verted into the original speech or writing. There are natural laws
which limit the amount of intelligence or signal that can...

Antenna Handbook ____________________________ 
2-17
Figure 2-7. Bandwidth.BANDWIDTH=1.34 MHz
FREQUENCY, MHz 2.02.22.42.6
2.83.0
3.23.43.6
3.84.0 0 50 100
TUNED CENTER FREQUENCY
-15
-6
-9 -30
POWER OUTPUT
PERCENT OF POWER AT 3.0 MHz
DECIBELSINTELLIGENCEBANDWIDTH
Voice, AM6.0 KHz
Voice, FM46.0 KHz
One microsecond pulses10,000.0 KHz
Bandwidths necessary to transmit and receive 
some ordinary kinds of intelligence 

2-18 ____________________________________ 
MCRP 6-22D
TAKE-OFF ANGLE
The antenna’s take-off angle is the angle above the horizon that an
antenna radiates the largest amount of energy (see fig. 2-8). VHF
communications antennas are designed so that the energy is radi-
ated parallel to the Earth (do not confuse take-off angle and polar-
ization). The take-off angle of an HF communications antenna can
determine whether a circuit is successful or not. HF sky wave
antennas are designed for specific take-off...

Antenna Handbook ____________________________ 
2-19
Section II. Ground Effects 
Since most tactical antennas are erected over the Earth and not out
in free space, except for those on satellites, the ground will alter the
free space radiation patterns of antennas. The ground will also
affect some of the electrical characteristics of an antenna. It has the
greatest effect on those antennas that must be mounted relatively
close to the ground in terms of wavelength. For example, medium-
and high-frequency...

2-20 ____________________________________ 
MCRP 6-22D
 
Figure 2-9.  Quarter-Wave Antenna
Connected to Ground.
TYPES OF GROUNDS
When grounded antennas are used, it is especially important that the
ground has as high a conductivity as possible. This reduces ground
losses and provides the best possible reflecting surface for the
down-going radiated energy from the antenna. At low and medium
frequencies, the ground acts as a good conductor. The ground con-
nection must be made in such a way as to introduce...

Antenna Handbook ____________________________ 
2-21
The ground connections take many forms, depending on the type of
installation and the loss that can be tolerated. In many simple field
installations, the ground connection is made by one or more metal
rods driven into the soil. Where more satisfactory arrangements
cannot be made, ground leads can be connected to existing devices
which are grounded. Metal structures or underground pipe systems
are commonly used as ground connections. In an emergency, a...

2-22 ____________________________________ 
MCRP 6-22D
Counterpoise
When an actual ground connection cannot be used because of the
high resistance of the soil or because a large buried ground system
is not practical, a counterpoise may be used to replace the usual
direct ground connection. The counterpoise (fig. 2-10) consists of a
device made of wire, which is erected a short distance above the
ground and insulated from it. The size of the counterpoise should be
at least equal to or larger than the size...

Antenna Handbook ____________________________ 
2-23
In some VHF antenna installations on vehicles, the metal roof of the
vehicle (or shelter) is used as a counterpoise for the antenna. Small
counterpoises of metal mesh are sometimes used with special VHF
antennas that must be located a considerable distance above the
ground. 
Ground Screen
A ground screen consists of a fairly large area of metal mesh or
screen that is laid on the surface of the ground under the antenna.
There are two specific advantages...

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MCRP 6-22D
Section III. Calculating Antenna Length
An antenna’s length must be considered in two ways: physical and
electrical. The two are never the same. The reduced velocity of the
wave on the antenna and a capacitive effect (end effect) make the
antenna seem longer electrically than physically. The contributing
factors are the ratio of the diameter of the antenna to its length and
the capacitive effect of terminal equipment (e.g., insulators or
clamps) used...