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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.
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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