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