The Resurrection of CJ2-26

Rick G:

Many of the military radios built during WW II used the AM frequency, which was venerable to atmospheric and nearby static. The old AM radio in your earliest vehicle would play back static if your car did not have ignition suppression.  Even MVs near but not necessarily adjacent to a radio set would produce static and degrade the signal, especially in convoys. 

So to minimize static interference on AM radios, nearly all WW II military vehicles had ignition and body suppression installed at the factory. Early on both types of suppression employed many ground straps throughout the MB/GPW.  Later in the war capacitors replaced some of the ground straps as ignition suppression improved.   

Body panels that rubbed together would produce radio frequency (RF) signals that the enemy could pick up and locate using RF directional signal detectors. Even when closed, while traversing uneven ground the front of the jeep hood would rub against the radiator guard and, if the welt was worn down, produce RF signals. So higher-than-welt metal screws were installed in two holes along the top of the radiator guard, and the hood was tinned on the inside directly above those screws, to increase the grounding of the hood front to the jeep body to minimize RF signals. The hood was also grounded at each hinge by having short ground straps bolted with toothed lock washers to both the hood and body sides of the hood hinges (which due to their construction with the pin riding loose inside the loops never had constant grounding).  Other grounding straps were installed throughout the entire military jeep. 

Dedicated radio jeeps (that had radio sets permanently installed in them) ran their ignition system wires inside braided cables. Then some radio jeeps placed all ignition system components (coils, distributors, voltage regulators) inside cast aluminum or stamped steel housings to contain all RF signals. Very late in WW II rubber "O" rings were added at each end of the braided cables to make the ignition system waterproof.  All jeeps, Dodges and GMC Jimmys were scheduled to have waterproof ignition systems installed beginning in December 1945 for the invasion of Japan, but Harry Truman ended the war 3 months earlier, so those waterproof ignition systems were never installed in mass production.

FM radio sets were first used by the Connecticut State Patrol in 1939 to avoid the problem of AM static interference.  FM radio development leaped forward throughout WW II, and WW II military radio sets were the first to widely use FM frequencies.