[Premium-Rx] Loops at LF / MF

[Rick Warnett]

Morning all,
I have used a large loop in PNG for many years to receive everything down to
OMEGA frequencies - 10KHz. of course it is not all that great down there,
but a simple push pull FET balanced amp / Z converter works wonders. There
are several comercial and amateur products that do this - or you can just
use a FET amp chip. This allows you to place the loop as far from noise
sources as possible and a few meters can make a big difference.
My loop was 6M tall and 6M wide and hung from a tree with a light duty
rotator at the base, just 1.5M above the ground. As loops are H field this
does not seem to matter much although the first meter above ground makes
some difference.
I had 4 turns of 10G solid copper wire and the loop covered about 160KHz to
2MHz with 4 varactor diodes as remote tuning. The "Q" approached 400 and
this was probably what eventually killed the FET preamps when a closeby
lightning strike occurred.

I matched the amp to a 50 ohm coax run back to the house (about 30M) and
remote tuned and aimed the loop from there.
With wires spaced about 1" apart I still managed a >40db null which is great
for DF'ing fishing beacons, NDB's and broadcasters.

The receiver was a HF1000.

Cheers