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

3-6 _____________________________________ 
MCRP 6-22D
Attenuation
Transmission lines do not transfer all of the energy applied at one
end of the line to the opposite end. Attenuation is energy that is lost
when converted into heart, partially due to conductor (wire) resis-
tance. More energy is lost due to the insulation material used to
space the conductors (dielectric loss). Some insulating materials
(e.g., Teflon) have extremely low loss while others (e.g., rubber or
wood) have relatively high loss,...

Antenna Handbook ______________________________ 
3-7
MAKING THE BEST USE OF AVAILABLE 
TRANSMISSION LINES
It is often necessary to feed a balanced antenna (e.g., horizontal
dipole) with coaxial cable. While this is not considered good prac-
tice, it will perform satisfactorily under most conditions. When
coaxial cable is used for this purpose, it should run perpendicular to
the dipole wires for a distance greater than one-half of the length of
the dipole. This will help to prevent unwanted RF power from...

3-8 _____________________________________ 
MCRP 6-22D
the twin-lead equal to a half-wavelength or any multiple of a half-
wavelength. When possible, the twin-lead should be twisted so that
it forms a long helix with about one twist every thirty centimeters,
or so. Twisting helps to prevent transmission line radiation and
reduces noise pickup when receiving.
Twin-Lead Limitations
It is generally best not to use twin-lead or balanced line at frequen-
cies higher than about 200 MHz for three reasons.
First,...

Antenna Handbook ______________________________ 
3-9
moisture after prolonged outdoor exposure much better than the
clear type. The clear, colorless, twin-lead tends to crack after a few
months exposure to the Sun. It also begins to absorb moisture which
greatly increases energy loss.
Directly Connecting the Transceiver and Antenna
In many instances the transmitter or receiver may be connected
directly to the antenna wire without using a transmission line. This
is particularly true with indoor antennas...

3-10 ____________________________________ 
MCRP 6-22D
BALUNS
There are times when a balanced antenna must be used with a trans-
mitter or receiver which has an unbalanced output or input circuit.
While it is possible to make a direct connection between balanced
and unbalanced devices, it is certainly not good practice. A balun
can be used to transform energy from balanced to unbalanced
devices and vice versa. 
The word balun comes from balanced to unbalanced transformer.
Many balun types are easily...

Antenna Handbook ____________________________ 
3-11
Figure 3-3. Balun Placed at the Transmitter or Receiver.
Cable Connectors
Cable connector fittings are available for all standard transmission
lines. Although it takes some time to prepare the cable ends and sol-
der the fittings on, it may be well worth it later if rapid assembly or
disassembly of a communications system is necessary.
Balanced Antenna
It is highly desirable to use a receiving antenna which is balanced
with respect to ground. This...

Chapter 4
 HF Antenna Selection
The HF portion of the radio spectrum is very important to commu-
nications. Radio waves in the 3 to 30 MHz frequency range are the
only ones that are capable of being reflected or returned to Earth by
the ionosphere with predictable regularity. To optimize the proba-
bility of a successful sky wave communications link, select the fre-
quency and take-off angle that is most appropriate for the time of
day transmission is to take place.
Merely selecting an antenna that...

4-2 _____________________________________ 
MCRP 6-22D
ANTENNA SELECTION PROCEDURE
Selecting the right antenna for an HF radio circuit is very important.
When selecting an HF antenna, first consider the type of propaga-
tion. Ground wave propagation requires low take-off angle and ver-
tically polarized antennas. The whip antenna included with all radio
sets provides good omnidirectional ground wave radiation. 
If a directional antenna is needed, select one with good, low-angle
vertical radiation. An...

Antenna Handbook ______________________________ 
4-3
circuit uses either a bidirectional or a directional antenna. Normally,
the receiving station locations dictate this choice (see table 4-1).
Before selecting a specific antenna, examine the available construc-
tion materials. At least two supports are needed to erect a horizontal
dipole, with a third support in the middle for frequencies of 5 MHz
or less. If these supports or other items to use as supports are
unavailable, the dipole cannot be...

4-4 _____________________________________ 
MCRP 6-22D
The site is another consideration. Usually, the tactical situation
determines the position of the communications antennas. The ideal
setting would be a clear, flat area (i.e., no trees, buildings, fences,
power lines, or mountains). Unfortunately, an ideal location is sel-
dom available. Choose the clearest, flatest area possible. If the pro-
posed site is obstructed, try to maintain the horizontal distance
listed in table 4-2. Often, an antenna must...