Mikes, Mikes......


Microphones were an essential part of WWII aircraft avionics, but the two basic mikes used today by military collectors and radio amateurs are typically more from the late 1930s and the early part of the war. Their hand-held operation was fine when all you had in front of you was a stick and a throttle, but the increasing needs of combat, not to mention the need for oxygen, drove the development of several "hands-free" variations. The earliest was the throat microphone, an infernal device that was later described by Bell Laboratories engineers as "a good idea but for the fact that the sound available from the larynx is basically unintelligible". Higher altitudes forced the use of oxygen masks and offered a much better solution for intelligibility through an integrated microphone element located in the mask. Because of their specialization (throat and oxygen masks are not the most user friendly) and impracticality (in a ham shack at least), the hands-free alternatives are left to the research of the reader. The one exception is the H-46 boom mike headset shown at Headphones, which details some of the earphone variations used during the war.

The US air services very early settled on carbon mikes for a number of reasons. They were pretty near indestructible, they needed very little amplification, and there was already a vast manufacturing infrastructure created by the telephone industry. Their shortcomings were few: carbon granules gradually became cemented over time, causing loss of response, but flyers soon learned that rapping the microphone sharply on a metal part of the airframe would jar the granuales loose and restore the volume. Carbon mikes also have an inherent white noise spectrum output even with no sound on the diaphragm, but in a noisy cockpit that was the least of anyone's worries.

In contrast, the British opted for a dynamic microphone for their aircraft, significantly superior to the carbon mike from an intelligibility standpoint but tending to be more delicate and requiring an extra amplifier stage in their radio sets/interphone systems to accommodate the lower output. The rapid proliferation of combined US/Commonwealth operations generated several workarounds on the US side, including an amplifier to use British mikes in US aircraft, and an attenuator to use American carbon mikes with the SCR-522, for example.

The USAAC was pretty much stuck in a rut by 1941, settling on the venerable T-17 that is so familiar to just about everyone. It replaced several "lollipop" designs used widely through the 1930s, and had the advantage of not requiring a separate "push to talk" switch. It was also used in much of the ground equipment during WWII, resulting in its wide availability on the surplus market after the war. The T-17 is probably the most abused microphone ever made. Just hang it on a convenient screw or toss it on the floor and forget it until you need to use it. However, there was at least one effective "official" hanger made for it, shown at left. This one has only a manufacturer's number on it, not a Signal Corps nomenclature. It used a PL-68 microphone plug that was eventually renomenclatured as a PJ-068.


T-17 Microphone and its hanger


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Naturally, the Navy couldn't use a Signal Corps microphone because it might contaminate their salty tradition, so they used what has become an incredibly long lived design called the RS-38, or in Navy-speak, the NAF 213264-6... with an NAF 212938-1 plug on the end. There was essentially no difference between the Navy plug and the PL-68, except at the base of the shaft where it entered the wiring end, there is a .303" diameter by .093" ferrule added there to provide a salt spray baffle. A matching recess in the phone jack created a trap to resist spray in shipboard installations. At the same time, absence of the recess did no harm to operation in those equipments that had a more protected environment. It is possible to purchase a new RS-38 style mike with an updated dynamic or electret element even today, though they aren't made in the US anymore.

There were two different types of microphone hangers produced for this microphone. The one on the right has an irritating habit of scratching your new/old -38 unless you polish the sharp edges with a rubberized abrasive wheel, so use it with care.

RS-38 mike and its hanger (Type CVA 10189)








Another RS-38 mike hanger (Type CMX 10144)


Photos abound of actual installations in aircraft, but the photo below may be of interest as it shows an RS-38 microphone hanger in the cockpit of an OS-2U Kingfisher, the float plane typically carried on the fantail of a battleship for reconnaissance.


Typical Navy 10144 mike bracket installation, this one in the rear seat of an OS-2U Kingfisher

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