Admittedly, we all want that engine to have been found on Gardner and have been on Amelia's AC . As discussed above, I just don't think it was. This is, in part, due to the operator and also the nature of the equipment. There are parts of the world where this phenomenon may be heard today. It shouldn't be too difficult if you have an HF receiver.
Night is best.
Lots of fade, reflection and overlapping signals. All the good stuff that make flying interesting. BTW, I have heard the radio transmissions of pilots as they confronted potentially fatal situations, and the monotone doesn't change. All the technical talk about AEs antennas, radios and DF and be pretty confusing to the neophyte, but I would like to emphasize its importance to help solve the riddle, and how difficult it is to get everything right. Experience has told us otherwise.