Section VII. RADIO INTERFERENCE SUPPRESSION
4-14. General Methods Used To Attain Proper Suppression
a. 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.
b. The term interference as used herein applies to electrical disturbances in the radio frequency range which are
generated by the special warfare printing plant and which may interfere with the proper operation of radio receivers or
other electronic equipment, or may enable the enemy to locate the equipment.
c. The term interference suppression as used herein applies to the methods as used to eliminate or effectively reduce
radio interference generated by the special warfare printing plant.
d. The items of equipment which make up the press unit of the special warfare printing plant have been chosen to
meet military requirements for radio interference suppression. All electric motors are either of the brushless type or,
have built-in suppression features. The shelter construction is such that radio interference from the fluorescent lighting or
other equipment is greatly reduced.
4-15. Interference Suppression Components
The equipment installed within the shelter system which could cause radio interference includes motors installed in the
duplicating machine, paper cutter machine, and air conditioner and the fluorescent lighting used for shelter and light table
a. Motor Suppression. Motor suppression is achieved through the use of capacitors and appropriate shielding.
Reference should be made to the applicable technical publication for the type and location of equipment radio
b. Fluorescent Lighting Suppression. Fluorescent lamps contain mercury vapor at low pressure. This vapor is
ionized by a flow of electrons in the tube. The de-ionization that follows causes ultraviolet radiation which excites the
internal phosphor coating causing it to radiate and give off light. The electron stream, or arc, in the tube is a source of
radio interference. The interference may be radiated from the lamp or the power leads, or transmitted by conduction
through a common power system. For systems that use starters, a capacitor may be placed across the starter terminals.
Systems without starters usually have built-in capacitors mounted in the ballast, or current limiting device. It is
impossible to suppress direct radiation from fluorescent lamps since shielding defeats the purpose for which the lamps
4-16. Replacement of Suppression Components
Refer to the applicable technical publication for removal and installation of suppression components used in the
duplicating machine, paper cutter, machine, and air conditioning system.
4-17. Testing of Radio Interference Suppression Components
Test capacitors or leaks and shorts on a capacitor tester; replace defective capacitors. If test equipment is not
available and interference is indicated, isolate the cause of interference by the trial and error method of replacing each
capacitor in turn until the cause is located and eliminated.