Terra TX 760D, Руководство по эксплуатации и установке

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2-4
Revision A
November 25, 1996
2.3.3 WIRING AND HARNESSING (CONTINUED)
NOTE:
It is extremely important that units should be installed in trays while final
dress and bundling of the harness is accomplished to assure proper alignment
of connectors between tray and unit. Failure to do this may cause problems
when unit is initially inserted into tray due to misalignment of connectors!
The final step is to perform a complete check of all avionics operations and insure
that free movement of all cockpit controls is available.
2.3.4 NOISE AND INTERFERENCE
The typical airframe is a small and imperfect platform for providing all of the
antenna ground planes and power sources and inter-wiring required for avionics
operations, particularly for a low noise and interference free expectation. This
subject is far too broad and complex to address in detail in a few paragraphs.
However, an approach to categorizing and defining the problem can be outlined.
Noise and/or interference is usually heard in the audio systems, although it may also
be detected as an interference to indicator operation. Unless a strong suspicion of the
exact source is suspected, it is best to begin a process of elimination, in the following
order:
1. Power Source: Check for low voltage when the avionics load is applied. A
high resistance battery cell in the A/C can cause numerous problems. View
the avionics power line at the avionics master and at the affected unit for
noise on the power line. If present, try to categorize the frequency (eg.
alternator whine, which may be caused by one or more bad alternator diodes,
or if interference is present only when a communication unit is transmitting,
etc.). If the noise is present or worse at the affected unit than at the avionics
master, investigate the harness for noise coupling between wires. If
necessary, disconnect the affected unit power from the aircraft power source
and connect to an external power supply or battery.
2. Power Ground: View the power ground line at the avionics master and the
affected unit. If noise is discerned at the master source, ground strapping
may be corroded or partially broken. If only at unit, a larger wire size or
wire re-routing may be required.
3. Interference: Both noise and interference may be either conducted or
radiated, and in some cases electromagnetically coupled between units. If it
is determined that the noise or interference is eliminated whenever another
avionics unit is not transmitting, first investigate the radiated alternative.
Insure complete and proper bonding of antennas to the aircraft surface, and
check the coaxial cable and all shield connections and connectors. Review
the manufacturer’s recommendations for antenna separations. Be aware that
antenna radiation directly to conductors at the rear of mounting trays or units
may occur if shields are stripped too far back from the connector or are
improperly grounded. Disconnecting the interfering antenna and substituting
an external dummy load may assist diagnosis.