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

							Antenna Handbook ______________________________ 
6-9
For best performance, construct the antenna longer than necessary,
then shorten it, as required, until best results are obtained. Connect
the radio set’s ground terminal to a good Earth ground for func-
tional efficiency. 
Center-Fed Doublet Antenna 
The center-fed doublet is a half-wave antenna consisting of two
quarter-wavelength sections on each side of the center. See figure
6-6 on page 6-10 for constructing an improvised doublet antenna
for use with FM radios. INSULATORSGROUND STAKE ANTENNA 
WIREWOODEN MAST
Figure 6-5. End-Fed Half-Wave Antenna. 
						

							6-10 ____________________________________ 
MCRP 6-22D
Doublet antennas are directional broadside to their length, which
makes the vertical doublet antenna essentially omnidirectional. The
radiation pattern is doughnut shaped. The horizontal doublet
antenna is bidirectional. 
Compute the length of a half-wave antenna by using the formula in
chapter 4. Cut the wires as closely as possible to the correct length
because the antenna wires’ lengths are important. 
A transmission line conducts electrical energy from one point to
another and transfers the output of a transmitter to an antenna.
Although it is possible to connect an antenna directly to a transmit-
ter, the antenna generally is located some distance away. In a vehic-
ular installation, for example, the antenna is mounted outside, andWOODEN 
MASTQUARTER- WAVEQUARTER- WAVEGROUND STAKEINSULATORSFigure 6-6. Center-Fed Doublet Antenna. 
						

							Antenna Handbook ____________________________ 
6-11
the transmitter is inside the vehicle. A transmission line, therefore,
is necessary as a connecting link. 
Center-fed half-wave FM antennas can be supported entirely by
pieces of wood. See figure 6-7 (A) for a horizontal antenna of this
type. See figure 6-7 (B) for a vertical antenna. These antennas can
be rotated to any position to obtain the best performance. If the
antenna is erected vertically, the transmission line should be
brought out horizontally from the antenna for a distance equal to at
least one-half of the antenna’s length before it is dropped down to
the radio set. VERTICALLY
POLARIZED HORIZONTALLY
POLARIZED ABINSULATORSQUARTER-
WAVETRANSMISSIONLINEFigure 6-7. Center-Fed Half-Wave Antenna. 
						

							6-12 ____________________________________ 
MCRP 6-22D
A short, center-fed half-wave antenna is shown in figure 6-8. The
antenna ends are connected to a piece of dry wood (e.g., a  bamboo
pole). The bend in the pole holds the antenna wire straight. Another
pole, or bundle of poles, serves as the mast. 
Figure 6-9 shows an improvised vertical half-wave antenna. This
technique is used primarily with FM radios. In heavily wooded
areas it is effective for increasing the range of portable radios. TheBAMBOO POLES
LASHING
WIRE1 TURN LOOP
1 TURN LOOPQUARTER-WAVEQUARTER-WAVEFigure 6-8. Bent Bamboo Antenna. 
						

							Antenna Handbook ____________________________ 
6-13
top guy wire can be connected to a limb or passed over the limb and
connected to the tree trunk or a stake. GROUND 
STAKEGROUND STAKEINSULATORINSULATORINSULATORINSULATORANTENNA WIREANTENNA
 WIREFigure 6-9. Improvised Vertical Half-Wave Antenna. 
						

							6-14 ____________________________________ 
MCRP 6-22D
FIELD EXPEDIENT DIRECTIONAL ANTENNAS 
The vertical half-rhombic, the long wire, and the yagi are field
expedient directional antennas.
Vertical Half-Rhombic and Long-Wire Antennas
The vertical half-rhombic antenna (fig. 6-10) and the long-wire
antenna (fig. 6-11) radiate a directional pattern and primarily trans-
mit or receive HF signals. They consist of a single wire, preferably
two or more wavelengths, supported on poles at a height of  3 to 7
meters (10 to 20 feet) above the ground. The antennas also operate
satisfactorily as low as 1 meter (approximately 3 feet) above the
ground. Connect the far end of the wire to a ground through a non-
inductive 500- to 600-ohm resistor. To ensure the transmitter’s out-
put power does not burn out the resistor, use a resistor that is rated
at least one-half the wattage output of the transmitter. Use a reason-
ably good ground (e.g,. a number of ground rods or a counterpoise)
at both antenna ends.  
Yagi Antenna
The Yagi antenna (fig. 6-12) is a dipole with an additional wire
behind it (reflector) and an additional wire in front of it (director).RESISTORFigure 6-10. Vertical Half-Rhombic Antenna. 
						

							Antenna Handbook ____________________________ 
6-15
These additional wires increase the power to the front of the
antenna while decreasing the power to the rear.Figure 6-11. Long Wire Antenna.SPLIT CABLE BOARDANTENNA 
MASTWD1/TT WIREROPEQUARTER- 
WAVEQUARTER- WAVEONE-HALF WAVE1/8WAVE10’Figure 6-12. Yagi Antenna.RESISTORRESISTORRESISTORRESISTOR 
						

							6-16 ____________________________________ 
MCRP 6-22D
Vee Antenna
The vee antenna is another field expedient, directional antenna. It
consists of two wires forming a vee with the open area of the vee
pointing in the desired direction of transmission or reception (see
fig. 6-13). The antenna must be fed by a balanced transmission line.
Sloping Vee Antenna
To simplify construction, the legs may slope downward from the
apex of the vee (this is called a sloping vee antenna [see fig. 6-14]).INSULATORS10’10’10’
Figure 6-13. Vee Antenna. 
						

							Antenna Handbook ____________________________ 
6-17
The angle between the legs varies with the length of the legs in
order to achieve maximum performance. INSULATORSINSULATORRESISTORSRESISTORFigure 6-14. Sloping Vee Antenna. 
						

							6-18 ____________________________________ 
MCRP 6-22D
Use table 6-1 to determine the angle and length of the legs..
When the antenna is used with more than one frequency or one
wavelength, use an apex angle that is midway between the extreme
angles determined by the chart.
To make the antenna radiate in only one direction, add noninductive
terminating resistors from the end of each leg (not at the apex) to
ground. The resistors should be approximately 500 ohms and have a
power rating at least one-half of the transmitter’s output. Without
the resistors, the antenna radiates bidirectionally, both front and
back.  Table 6-1. Leg Length and Angle 
for Vee Antennas.
Antenna 
Length 
(Wavelength)Optimum Apex 
Angle 
(Degrees)
190
270
358
450
640
835
1033