Here's a little bit of info' on RDF antenna:
Airplanes in flight accumulate electric charges52,53 that cause radio noise interference.
O.K., I've been having fun but now it's time to cut to the chase. At the risk of giving away my age, when I was young (make that VERY young) I had an AM radio on the nightstand next to my bed. I would fall asleep listening to soft music in my bedroom lit by the warm orange glow from the radio's tubes shining out through the ventilation holes in the back of the radio. (For those who do not know what a radio tube looks like, I am attaching a photo of several types and also
go here.) The back of the radio was made out of some kind of fiberboard. When I removed the back (they were made easy to remove so that you could replace the tubes when they burned out) I found the loop antenna mounted on the inside of the back. It was designed to work on the AM broadcast band, 535 kc to 1600 kc, just slightly above the "beacon band" (190 kc to 535 kc) which was the band used for radio direction finders, it still is. This is where the standard direction finder frequencies used in Earhart's time, 375 kc, 400 kc and 500 kc, 800 meters, 750 meters and 600 meters wave lengths. Itasca was transmitting homing signal on 500 kc/600 meters. The loop antenna inside my radio consisted of dozens of turns, or coils, of wire. There was a reason for this.
It turns out that a loop antenna designed for direction finding should contain a length of wire equal to 0.08 wavelength for optimum performance but it can also be tuned to work on nearby frequencies. So the loop antennas used on aircraft radio direction finders do not have just one or two coils, but many coils. Do the math. Looking at the photo of Earhart mugging with the antenna, it appears that the loop is about one foot (30 cm) in diameter. Multiply by Pi and the circumference is a little more than three feet, let's call it one meter. The loop was designed to cover wavelengths between 600 to 1500 meters, let's say it was optimized for the standard direction finder wavelength of 800 meters. Multiply the 800 meters by 0.08 and you find the amount of wire in the loop is 64 meters long. Since the circumference of Earhart's loop is about one meter then there had to be 64 coils of wire inside it. The picture from the ROV shows only two coils
so it ain't an RDF antenna. (And yes, they use very fine wire so 64 meters does fit inside the static shield.)
Also, the static shield has to be made out of a non-magnetic, conducting material, usually copper or aluminum. Where did that go?
(Does anybody else remember the tube testing machines which, at least in Chicago, were found in drugstores, for some reason. When your radio stopped working you pulled the tubes and carried them down to the drugstore. Looking at a table on the self test machine, you found the listing for your tube, placed it in the right sized socket, followed the instructions for your type of tube, set the various switches and then read the meter. If the reading was not in the correct range then you had found the bad tube and you bought a replacement tube, they were kept in a locked cabinet making up the base of the testing machine, you had to call the druggist over. If the first tube tested O.K. then you tested the rest of your tubes until you found the bad one. Too bad Earhart didn't have a tube tester machine.)
gl