Antenna Handbook MCRP 3-40.3C (Formerly MCRP 6-22D)

2-26

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MCRP 6-22D

Section IV. Antenna Orientation

The orientation of an antenna is extremely important. Determining the position of an antenna in relation to the points of the compass can make the difference between a marginal and good radio circuit.

AZIMUTH

If the azimuth of the radio’s path is not provided, determine it by the best available means. The accuracy required depends on the radiation pattern of the directional antenna. If the antenna beamwidth is very wide (e.g., 90° angle between half-power points) an error of

90°

HALF-POWER

POINTS 90°

270°

0°

270°

0°

180°

RELATIVE

FIELD STRENGTH

180°

RELATIVE

POWER

Figure 2-11. Beamwidth Measured on Relative Field Strength and Relative Power Patterns.

Antenna Handbook

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10° is of little consequence. In transportable operation, the rhombic and vee antennas may have such a narrow beam that great accuracy is required to determine azimuth. The antenna should be erected for the correct azimuth. Great accuracy is not required to erect broadbeam antennas.

Unless a line of known azimuth is available at the site, the direction of the path is best determined by a magnetic compass. Figure 2-12 on page 2-28 is a map of magnetic declination, showing the variation of the compass needle from the true north. When the compass is held so that the needle points to the direction indicated for the location on the map, all directions indicated by the compass will be true.

Improvement of Marginal Communications

It may not always be feasible to orient directional antennas to the correct azimuth of the desired radio path, and marginal communications may suffer. To improve marginal communications—

•

•

Check, tighten, and tape cable couplings and connections.

Retune all transmitters and receivers in the circuit.

• Check that the antennas are adjusted for proper operating frequency.

Change the heights of antennas. •

• Move the antenna a short distance away and in different locations from its original location.

• Separate transmitters from receiving equipment, if feasible.

2-28

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MCRP 6-22D

E 6

Figure 2-12. Magnetic Declination Over the World.

Antenna Handbook

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Transmission and Reception of Strong Signals

After an adequate site has been selected and the proper antenna orientation obtained, the signal level at the receiver will be proportional to the strength of the transmitted signal.

WARNING

EXCESSIVE SIGNAL STRENGTH MAY RESULT IN ENEMY IN-

TERCEPT AND INTERFERENCE OR IN YOUR INTERFERENCE

WITH ADJACENT FREQUENCIES.

If a high-gain antenna is used, a stronger signal can be obtained.

Losses between the antenna and the equipment can be reduced by using a high quality transmission line, as short as possible, and properly matched at both ends.

WARNING

BE EXTREMELY CAREFUL WHEN PUTTING UP, TAKING

DOWN, OR MOVING ANTENNAS LOCATED NEAR HIGH VOLT-

AGE OR COMMECIAL POWER LINES. ANTENNA CONTACT

WITH THESE CAN AND MAY RESULT IN ELECTROCUTION

OR SEVERE INJURY TO PERSONNEL HOLDING THE ANTEN-

NA OR THE CONNECTING GUY WIRES AND CABLES.

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