[600MRG] re. Loop Antennas

[Edward Larsen]

   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
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