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

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MCRP 6-22D
Antenna Within Vehicle Interior
Antennas located inside vehicles will lose some radiation through
the window openings. It is difficult to predict how much radiation
will escape or how much the original antenna radiation pattern will
be affected by the enclosure. The pattern modification depends on
the vehicle size and its openings and on the location of the antenna
inside. Select antennas which operate above the cutoff frequency of
the window...

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5-13
upset the impedance on the transmission line, causing unwanted
received or transmitted power loss. When using coaxial cable as
transmission line, use suitable, commercially available, low-loss
coaxial antenna switching relays if possible.
In the 225 to 400 MHz and 450 to 470 MHz frequency ranges, most
antennas are quite small. Mount two identical antennas, using one
for transmitting and one for receiving. Separate transmission lines
may then be used,...

Antenna Handbook ______________________________ 
6-1
Chapter 6
Field Repair and Expedients
Antennas sometimes break or sustain damage, causing poor com-
munications or communications failure. If a spare is available, use
it to replace the damaged antenna. When there is no spare, construct
an expedient antenna. The following paragraphs discuss antenna
and support repair and constructing and adjusting expedient anten-
nas. 
REPAIR TECHNIQUES 
Whip Antennas 
A broken antenna (whip) can be repaired...

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MCRP 6-22D
Wire Antennas 
Expedient wire antenna repair may involve repairing or replacing
the antenna or transmission line wire or repairing or replacing the
assembly that supports the antenna. When one or more antenna
wires are broken, repair the antenna by reconnecting the broken
wires. Lower the antenna to the ground, clean the ends of the wires,
and twist the wires together. Solder the connection if possible. If the
antenna is damaged beyond repair,...

Antenna Handbook ______________________________ 
6-3
be used as field expedient insulators (fig. 6-2). The best are plastic
or glass, including plastic spoons, buttons, bottle necks, and plastic
bags. Less effective than plastic or glass, but better than no insula-
tors at all, are wood and rope, or both, in that order. The radiating
element—the actual antenna wire—should touch only the antenna
terminal and be physically separated from all other objects, other
than the supporting insulator.PLASTIC SPOON...

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MCRP 6-22D
Guys 
Lines used to stabilize antenna supports are called guys. These lines
are usually wire, manila rope, or nylon rope. If a rope breaks, repair
it by tying the two broken ends together. If the rope is too short after
tying, lengthen it by adding another piece of rope or a piece of dry
wood or cloth. If a guy wire breaks, replace it with another piece of
wire. Figure 6-3 shows how to repair a guy line with a spoon. 
Masts 
Some antennas are...

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6-5
Guys used to hold antenna supports are made of rope or wire. To
ensure that wire guys will not affect antenna operation, cut the wire
into several short lengths and connect the pieces with insulators. Figure 6-3. Repaired Guy Line and Mast. 

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MCRP 6-22D
Adjusting the Antenna 
An improvised antenna may change a radio set’s performance. Use
the following methods to determine if the antenna is operating prop-
erly. 
Use a distant station to test the antenna. If the signal received from
this station is strong, the antenna is operating satisfactorily. If the
signal is weak, adjust the antenna and transmission line height and
length to receive the strongest signal at a given receiver volume
control...

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6-7
The power reflected from the load interferes with the incident (for-
ward) power, creating standing waves of voltages and current along
the line. The ratio of standing-wave maximal to minimal is directly
related to the impedance mismatch of the load. The standing-wave
ratio (SWR) provides the means to determine impedance and mis-
match. 
FIELD EXPEDIENT ANTENNAS
VHF Considerations
SINCGARS VHF radios provide the primary means of communica-
tions means...

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MCRP 6-22D
End-Fed Half-Wave Antenna 
Construct an expedient, end-fed half-wave antenna from available
materials (e.g., field wire, rope, and wooden insulators). This
antenna’s electrical length is measured from the antenna terminal
on the radio set to the far end of the antenna (fig. 6-5). Figure 6-4. Field Substitutes for Support of
Vertical Wire Atennas.