At the start of World War II, the US Army recognized the importance of reducing radio frequency noise in its vehicular fleet. Any electrical device that produces a spark can emit incidental radio signals or “noise” which can interfere with the operation of radio communication equipment and also allow the enemy to detect the presence and location of vehicles.
Radio suppression on 1/4-ton trucks was accomplished using a combination of continuous grounding and capacitive filters. Capacitive filters are electronic components known as capacitors or condensers mounted close to the source of radio frequency energy. These capacitors direct the high frequency energy directly to vehicular ground before they can reach wiring that can act as an antenna. Vehicles on which suppression was factory-installed were tested and those which passed had the letter “S” (for suppression) painted on the cowl in blue drab
During the war, the radio suppression system was continuously improved to improve efficiency and reduce cost. 1/4-ton trucks had several versions of radio suppression systems between 1941 and 1945.
The Long Olive Drab Line is proud to have reproduced the first and only accurate reproductions of the radio suppression capacitors needed by restorers building factory-class restorations. By selecting and installing our ground strap and capacitive filter kits, you can be assured that your jeep will properly be outfitted as it was when it rolled off the assembly line. When you place the “S” on your jeep’s cowl, you’ll know that it marks the completion of a job well done.
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