Motorola Gm300 Installation Manual

							Noise Reduction Techniques2-7
3.2 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 depends 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.)
4.0 Noise Reduction Techniques
4.1 General
There are three basic ways to suppress noise. The first is the addition of resistance in circuits
subject to ringing. This method is used for the ignition coil HV cable, spark plug wires, and spark
plugs. The second is to filter noise from low voltage wiring using coaxial bypass capacitors. The third
is to control static charge build-up using wipers for movable parts such as automobile hoods and
trunk lids, or flexible bonding leads for fixed members. Static in wheels may also be controlled using
collector rings. Applications of each of these techniques are discussed below.
The vehicle manufacturer’s service manual also may provide noise suppression information which is
valuable in any first attempt at noise suppression. 
						

							2-8REDUCING NOISE INTERFERENCE
4.2 Ignition System Interference
4.2.1 Engine Maintenance and Tune-Up
The most important step in reducing ignition noise is insuring that the engine is in proper tune. Pay
particular attention to the following points if the noise interference from the ignition system is severe:
1.Be sure the spark plugs distributor points, and condenser are in good condition.
2.Be sure ignition timing is properly adjusted.
3.Be sure the distributor cap and rotor are in good condition. They should be replaced at least
every 30,000 miles.
4.Be sure that spark plug wires make good, solid contact at each end and are routed as far as
possible from low voltage leads.
5.Many late-model automobiles are equipped with a shield over the distributor points. Check to
see that this shield is properly positioned and securely attached.
4.2.2 Available Noise Reduction Kits
Motorola offers two noise reduction kits: Model TLN8845_ for alternator-equipped vehicles; Model
TLN6252_ for generator-equipped vehicles. These kits are for suppression of noise in the primary
and secondary of the ignition coil and for bleeding of static charges on the hood. The TLN6252_
also is used to suppress noise from the generator and voltage regulator. Figure 2-3 TLN8845_
Noise Reduction Kit for Alternator-Equipped Vehicles and Figure 2-4 TLN6252_ Noise Reduction Kit
for Generator-Equipped Vehicles show the contents of the kits and their usage.
Motorola also offers wheel static collectors (Motorola Part No. 0100534254-regular type and
0100563173-small type). Use of these items are described in section 4.7 Wheel Static on page 12.
Most auto parts dealers can supply 0.05 µF bypass capacitors (condensers), resistive ignition wires,
and resistor spark plugs. The type of spark suppression used in noise reduction should always be in
accordance with the recommendations of the vehicle manufacturer, that is, if spark plugs are to be
replaced with built-in suppressor types, they should be in the proper heat ranges and thread sizes
for the particular engine. In each ignition system, there is a maximum amount of resistance that may
be connected between the distributor and a spark plug. If resistance-type ignition wire is used, the
length of each wire must be limited so that its resistance does not exceed the allowable maximum.
4.2.3 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 2-5 Ignition
Coil Noise Suppression). 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. 
						

							Noise Reduction Techniques2-9
4.2.4 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.
4.2.5 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.
4.3 Alternator/Generator Whine
This type of interference is characterized by a high-pitched whine which varies with engine speed. A
0.5 µF coaxial capacitor (Motorola Part No. 0882571B01) can be used to bypass the whine. For
generators, the capacitors is connected in the armature lead. Never use a capacitor in the field lead.
Use the field suppressor assembly supplied in the TLN6252_ Noise Reduction Kit. For alternators,
the capacitor is connected in the lead to the battery post (see Figure 2-6 Generator Whine
Suppression and Figure 2-7 Alternator Whine Suppression).Figure 2-5Ignition Coil Noise Suppression
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.Step 4.
Connect capacitor
lead to battery post.
From distributor
Distributor Post
Battery Post
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							2-10REDUCING NOISE INTERFERENCE
Figure 2-6Generator Whine Suppression
Figure 2-7Alternator Whine Suppression
Step 1.
Mount Capacitor
(0.5µF Coaxial Type)
under generator ground screw.Step 3.
Connect wire lead to capacitor
using lockwasher and nut.
Step 4.
Connect capacitor
lead to armature post.
Caution:
Do not connect
capacitor to field teminal.
Step 2.
Disconnect wire (dashed)
from armature post and 
connect to capacitor using
lockwasher and nut.
FL0830310-O
Step 1.
Mount Capacitor to
(0.5µF Coaxial Type)
under alternator
ground screw. Step 2.
Disconnect wire from
battery post and connect
to capacitor using
lockwasher and nut.
Step 3.
Connect wire lead to capacitor
using lockwasher and nut.
Step 4.
Connect capacitor
lead to battery post.Caution:
Do not connect 
capacitor to field terminal.
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							Noise Reduction Techniques2-11
4.4 Voltage Regulator Noise
This type of interference is characterized by erratic popping noises which change only slightly with
changes in engine speed. The noise is generated by arcing in the vibrating breaker contacts of the
voltage regulator. It can be suppressed by connecting a 0.5 µF coaxial capacitor (Motorola Part No.
0882571B01) in the battery and armature leads of the voltage regulator (see Figure 2-8 Voltage
Regulator Noise Suppression).
4.5 Hood and Trunk Lid Noise
This type of noise is characterized by irregular popping sounds. It is caused by friction in poorly
bonded automobile hoods or trunk lids. This friction causes static electricity to build up until arcing
occurs. This type of noise is suppressed using a Motorola Hood Wipers and Mounting Hardware Kit
(part of TLN8845_ or TLN6252_ Noise Reduction Kits) which provides electrical bonding of the
hood or trunk to the vehicle body while permitting them to be opened.
CAUTION: Disconnect the battery ground terminal before attempting to connect components
to the voltage regulator.
Figure 2-8Voltage Regulator Noise Suppression
!
Step 1.
Mount Capacitor
(0.5µF Coaxial Type)
to vehicle chassis
using lockwasher and
self-tapping screw.  Vehicle
Step 2.
Disconnect wire (dashed)
from battery post and
connect to capacitor
using lockwasher and nut.Step 3.
Add lead from battery
post to capacitor using 
lockwasher and nut.
Armature
A coaxial capacitor can
be added here, if required.
Battery
Post
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							2-12REDUCING NOISE INTERFERENCE
4.6 Other Electrical Noises
Other elements of the electrical system which can generate noise are listed below. These can be
suppressed by connecting a 0.5 µF bypass capacitor between the noise source and ground.
1.Ammeter-to-battery lead
2.Gauges (oil, fuel, temperature)
3.Ignition Switch
4.Lamp bulbs (headlamps, tail lamps, dome lamps, etc.)
5.Accessory wiring (electrical fuel pump, electric windshield wipers, heater fan motor, window
openers, etc.)
4.7 Wheel Static
Road friction can cause static build-up on the front wheels. Suppress noise from this source using
wheel static collector rings (Motorola Part No. 0100534254 regular type - 0100653173 small type).
4.8 Ground Bonding
If a vehicle is not properly bonded to ground, static charges can increase. This increase can cause
noise from electrical arcing. This type of noise is suppressed by bonding the part using one-inch
wide ground straps (keep them as short as possible). Some common points where bonding may be
helpful are listed below (see Figure 2-9 Ground Bonding).
A. From engine block to the firewall.
B. From engine block to vehicle frame at points where the engine is shock-mounted.
C. From the battery ground terminal to the vehicle body.
D. From top of front wheel “A” frames to chassis, par ticularly in cases where rubber-mounted
members are used.
Figure 2-9Ground Bonding
Battery
Firewall
ChassisFender
Well
Front Wheel
A Frame
B A
C
D D
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