Tune-up
In most mobile installations, ignition noise is a problem.
Before beginning any special noise suppression steps, be sure that the
vehicle is well-tuned. Clean and tighten all electrical connections,
including alternator, battery, regulator and coil connections. Perform
the following maintenance steps as necessary. Solder any crimped
spark plug or distributor leads; clean and regap or replace spark
plugs and ignition points; and check and clean alternator rings or
generator brushes. Retune the engine at the manufacturer's recom-
mended intervals.
Corrective Steps
Usually several sources of noise are present in any vehicle, with the
strongest covering the others. In order to find and eliminate the
maximum number of noise sources, you will have to start with the
strong sources and then work back. To be sure the noise you hear
comes from your vehicle and not outside it, drive to a relatively
quiet location (free of man-made electrical interference such as noisy
power lines, industrial noise or other vehicles). Test for noise with
a weak signal on the channel and the engine off. Then start the
engine. Ignition noise will probably be present at all engine speeds.
If it is severe, it may make a normally readable signal unreadable.
To reduce ignition noise, install resistor-type spark plugs if these
are not already installed. If non-resistance ignition wiring is used,
install a 10k-ohm suppressor resistor at each spark plug tower of
the distributor. Install a coaxial capacitor at the ignition coil primary
as close to the coil primary as possible. This capacitor can be purchased
from an electronics parts company or an automotive electrical service
company.
A "whining" noise which varies with engine speed and continues
with the ignition turned off and the vehicle coasting in gear is char-
acteristic of the alternator. Check and clean it and install an alternator
filter (same sources as above).
An irregular, clicking sound which disappears at a slow idle charac-
terizes the voltage regulator. Install a 4-ohm carbon resistor as close
to the field terminal of the regulator as possible, then a .002
11
F
capacitor in series with and as close to the resistor as possible. Con-
nect the capacitor to ground. See the detail drawings of Figure 4.
Irregular popping noises which vary with road surfaces indicate
static discharge at any of several locations in the vehicle. Tighten
loose nuts and bolts and bond large areas such as the fenders, exhaust
pipe, firewall, etc. to the frame with lengths of heavy wire braid.
More Help
Figure 4 illustrates these noise suppression steps. Additional infor-
mation is available in the Radio Amateur's Handbook published by
the
ARRL
