This is fascinating, and brings up some questions -

Is this coil double wrapped? I cannot quite tell from the photos.

On a ferrite rod assembly like this, the coil(s) wrap around only a
small portion of the rod. Noting this, will the rod still transfer
signal along its entire length? In other words, can a shorter rod be
used as effectively?

Is there any value to wrapping the coil(s) more widely spaced along the
length of the ferrite?

Thanks,
Bruce Jensen