TM 9-2350-256-20-1
UNIT MAINTENANCE
RECOVERY VEHICLE, FULL TRACKED: MEDIUM, M88A1
NSN 2350-00-122-6826, EIC AQA
RADIO INTERFERENCE SUPPRESSION THEORY OF OPERATION
Radio Interference Suppression
Radio interference suppression is the elimination or minimizing of electrical disturbances which interfere with radio reception
or disclose the location of the vehicle to sensitive electronic detectors. It is important, therefore, that all vehicles be suppressed
properly to prevent interference with radio reception by the same vehicle, neighboring vehicles, or installations. Essentially,
suppression is attained by providing a low-resistance path to ground for stray currents. The methods used include shielding the
ignition and high-frequency wires, grounding the frame with bonding straps, and using capacitors and resistors.
Interference Suppression Components
1.
Preheat system.
a. High-tension cable. The high-tension cable to the spark plug preheater consists of an inner conductor which
carries the high voltage to the spark plug, and an outer braided conductor which serves as a shield and also
grounds the metal exciter housing to the spark plug housing. The exciter housing is also grounded to the ve-
hicle engine through one of the leads (connected to terminal B) in the exciter power input cable.
b. Spark plug. The spark plug is integrally shielded and contains an integral resistor-suppresser.
2.
Generating systems. The engine generator and auxiliary engine generator are radio interference suppressed in an
identical manner by use of feedthrough capacitors. These feedthrough capacitors are mounted on and extend through
the side of the junction box mounted on the generators. The mounting frames of the capacitors are grounded to the box
by means of tooth-type lockwashers. The armature circuit capacitor valve is 1.75 microfarads (mfd), and rated at 100
V dc at 300 A. The field and interpole circuit capacitors are both 0.25 mfd, and rated at 100 V dc at 10 A. The blower
attached to the engine generator also has a 0.25-mfd, 100-V dc, 20-A, feedthrough capacitor in series with each power
lead.
3.
Personnel heater. The personnel heater fuel pump is integrally suppressed by means of a feedthrough capacitor. A
0.25-mfd, 100-V dc, 20-A, feedthrough capacitor mounted on the motor housing is in series with the blower motor
positive power input lead.
4.
Ventilating blower. A 0.1-mfd, feedthrough capacitor mounted in the motor housing is inserted in series with the
power input lead of the blower. The power input lead between the blower and input power connector is also shielded
with braided cable.
5.
Roadwheels, track support rollers, and idler wheels. Static grounding springs are included in the roadwheels and track
support rollers. These coil steel springs function as grounding devices for static electricity developed by the wheels
and rollers when the vehicle is in motion.
Other Means
Feedthrough capacitors require good bonding or grounding to provide adequate radio noise suppression. Tinned copperbraid
bond straps, terminated in appropriate copper lugs and bonded by means of plated tooth-type lockwashers, are used for this
purpose when good contact between the component to be suppressed and ground is required. Where clearance is not a problem
and the component is mounted with bolts or other fasteners, plated tooth-type lockwashers are used to provide the grounding.
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