RF signal level

TM 11-490-5

with local instructions, such as soil treatment with a

(10) Antennas and transmission lines. Loose

chemical solution, if necessary. Special emphasis must

broken and corroded antenna and waveguide

be directed to the use of 3-wire grounding power cords

connections and tower guywires are a source of noise

for ancillary equipment and hand tools with the ground

which can be reduced through regular periodic

wire connected to the station ground.

inspection, cleaning, tightening, and other maintenance

(8) RF signal level.

Intermodulation and

measures. This is an important facet of installation and

crosstalk interference problems attributable to high

maintenance. For example, copper wire strung during

signal level will require adjustment to eliminate the

hot weather conditions can become taut and snap during

problems. Any attempt to adjust a signal level at the

cold conditions, if it was too tightly strung. Antenna

receiving station without a check of the levels

orientation can sometimes be varied slightly to avoid

throughout the system, however, may not solve the

interference pickup. Waveguide pressurization should

problem if it is caused by high signal level at channel,

be periodically checked in accordance with the

group, or supergroup levels of a previous station which

applicable specifications.

In the case of open

has resulted in baseband overloading. Signal level

transmission lines, proper connection at installation,

adjustment can be undertaken while the channels are in

orientation in relation to possible noise sources, and

service, depending on the severity of the interference

constant line spacing are important to the reduction of

problem, but usually this adjustment must be done out

interference problems.

of service with test tones applied.

e. Follow-On Procedures.

(9) Interfering transmitters. If it is determined

(1) The above procedures for the recognition,

that a station's own transmission is causing excessive

isolation, and remedy of EMC problems should be

interference to others and circumstances preclude a

sufficient to detect and correct most of the less complex

frequency change, a sideband change, or other similar

interference problems that normally occur to fixed and

solution, the interference problems could be reduced by

transportable facilities. Persistent, chronic occurrences

a slight reorientation of the transmit antenna (if this is

of EMC problems, particularly those which may occur

practicable) to move the interfering lobe away from the

upon activation of new systems within a site, will require

distant station suffering the interference.

Another

resolution by the supporting maintenance or engineering

possible solution could be to adjust the beam shape.

assistance personnel. However, it is essential that site

For example, if a "sloping V" antenna configuration is

operating personnel learn to recognize both EMC and

being employed as an HF transmitting antenna, it may

ECM problems and to distinguish between them.

be possible to decrease the apex angle of the antenna

(2) Reporting procedures are contained in the

to an optimum value of 30 degrees. The effective

following chapter.

change in beam shape may avoid transmission into a

nearby receiver. Suggestions for such a change should

be referred to senior station engineering staff.

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