Motorola Radius PM400 Installation Manual - Page 31
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Noise Reduction Techniques
10.2.3 Ignition Coil Interference
This type of interference is characterized by a popping sound which is most noticeable when the
engine is running slowly. To suppress the noise, connect a 0.1 µF coaxial capacitor (Motorola Part No.
0882571B02) from the battery side of the ignition coil to vehicle ground (see Figure Figure 10-1). This
keeps the distributor noise from being conducted through the battery lead into the electrical system of
the vehicle. Note that some electronic ignition systems do not route the battery lead to the ignition
coil; proper operation of the ignition system can be impaired if the "input" terminal is bypassed.
Step 3.
Connect wire lead to capacitor
using lockwasher and nut.
Step 1.
Mount Capacitor
(0.1 F Coaxial Type)
to vehicle chassis
using lockwasher
and self-tapping screw.
Step 2.
Disconnect wire (dashed)
from battery post and
connect to capacitor using
lockwasher and nut.
10.2.4 Distributor Interference
This type of interference is characterized by popping sounds which are present at all engine speeds.
It is caused by sparking between the rotor and the distributor cap inserts as the rotor turns. To
suppress this noise, use resistance ignition wire to connect the ignition coil to the distributor cap.
10.2.5 Battery Connections
The radio set power cable can pick up noise generated in the vehicle. This can be minimized by
connecting the power cable directly to the battery instead of the fuse block. The battery acts like a
large capacitor (about one Farad for a 50 amp/hour battery), which bypasses induced noise. The
battery ground lead should be securely bonded to the vehicle frame. Undesirable parallel ground
currents can be minimized by using the vehicle frame as a common ground point. If ignition switch
control of the radio is desired, the radio power leads may be connected to the battery through a relay
which is controlled by the ignition switch.
Figure 10-1. Ignition Coil Noise Suppression
Step 4.
Connect capacitor
lead to battery post.
23
From distributor
Distributor Post
Battery Post
FL0830264-O