Thanks for that link! Those are "basket-weave" coils. The method allows high inductance while reducing self capacitance, which could turn the coil into a stand-alone resonant circuit.

Doesn't hurt to kick around the old radio stuff, as that's where all the innovations we still use were made. A DSP chip only synthesizes what once took lumped components to achieve. To understand the new stuff you have to understand the old stuff. And after 100 years, we're still making antennas with Litz wire.

73,

Jim, KR1S
http://qrp.kearman.com/