Motorola Radius PM400 Manuel d'installation - Page 29
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Detection of Noise Sources
9.2
Sources of Noise
Some interference is due to geographic location. This interference does not need to be eliminated
since it is possible for the vehicle to be moved away from the interfering noise source. Noise from
power lines, fluorescent lights, and other vehicles (emitting high levels of radiated noise) are
examples of noise which depend upon location. Make certain that you are not attempting to suppress
noise in a vehicle while it is in a noisy location. If you suspect that your location is noisy, simply turn off
everything in the vehicle except the radio and listen to the remaining ambient noise. If the noise level
is objectionable, you may have to noise suppress the vehicle during a less noisy time of day or in a
different, quieter location.
Check the installed radio for conducted and inducted noise by using an unmodulated signal generator
to supply a clean RF signal through a coaxial cable directly to the antenna connector on the radio set.
This should prevent radiated noise from entering the receiver and masking conducted and induced
noise. Make certain that the signal generator is not microphonic and is placed away from the noise of
the engine and exhaust.
Operate the controls for fans, blowers, power windows, headlamps, turn signals, windshield wipers,
and other electrical accessories. Listen for the presence of noise in the received radio signal. This will
allow the source of the interference to be determined. Some noise sources cannot be turned on and
off at will. These sources will need to be attacked piecemeal on a trial and error basis: alternator
whine, voltage regulators, electric fuel pump, and other possible sources. Remember that induced
noise can result from radio wiring being too close to other vehicle wiring. This problem is most easily
solved by proper cable routing at the time of installation.
Radiated noise must be attacked after conducted and induced noise has been satisfactorily
suppressed. The vehicle ignition system is usually the primary source of this interference.
Antenna placement can be critical in some installations. Remember that static discharge generates
static or radiated noise and will probably be generated only when the vehicle is in motion.
Since radiated noise interference is most noticeable in weak signal areas, it is suggested that
suppression be finalized while listening to a weak "on frequency" signal. (The squelch should be
"open" so that even marginal signals can be heard.)
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