Motorola GM1200E Manuel d'installation - Page 32

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Noise Reduction Techniques

5.2.3

Ignition Coil Interference

This type of interference is characterised 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. 8C82571B02) from the battery side of the ignition coil to vehicle ground (see Figure 2-5). 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 and can have proper operation impaired if the "input" terminal is bypassed.

Step 3.

Connect wire lead to capacitor

using lockwasher and nut.

Step 1.

Mount Capacitor

(0.1µF 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.

5.2.4

Distributor Interference

This type of interference is characterised 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.

5.3

Battery Connections

The radio set power cable can pick up noise generated in the vehicle. This can be minimised 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/hr. battery), which bypasses induced noise. The

battery ground lead should be securely bonded to the vehicle frame. Undesirable parallel ground

currents can be minimised 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.

2-8

Figure 2-5 Ignition Coil Noise Suppression.

Reducing Noise Interference in Mobile Two-Way Radio Installations

Step 4.

Connect capacitor

lead to battery post.

From distributor

Distributor Post

Battery Post