Thanks Dave for the posting regarding loop antennas for VLF. I like your approach and if your loop is out-performing a good active whip it is certainly working.
I did some loop tests a few years ago. What I built was:
13 turns of silver plated AWG 22 stranded/teflon, 79" diameter, wires spaced 1/2" and crossed-over at the bottom (mobius wound).
About 725 uH inductance resonated to VLF with 80-1250pF varactor tuning capacitance. Loop self resonance was about 3.02 MHz. I used a one turn coupling loop inside which I adjusted for 50 Ohm match. I've found that a high-Q tunable loop eliminates any overload or intermodulation problems in a receiver.
I left this loop with KI6MTV when I moved to Arizona. I need to build another. It would tune about 140 kHz to 650 kHz via vari-cap diode tuning.
I have designed/built a pretty good active amplified ferrite rod antenna for 17.2 kHz. I can email you the schematic if you like. It too parallel resonates the high-Q loop for sharp narrow-band tuning. The circuit could be modified for higher frequencies if desired.
There has been a lot of excellent VLF loop design work in the past by several low frequency Gurus who published in the Lowdown magazine. Unfortunately this data is not available anywhere. I have most of the old Lowdowns going back to the 1980s.
Keep on experimenting!
73
Ed, KI6R
SaddleBrooke, Az