[Lowfer] WD2XES QRPP WOLF

[Bill de Carle]

At 11:57 AM 10/9/2010, Stan, W1LE wrote:
>   Hello Bill,
>
>Interesting application of a loop array.
>
>Are your loops:
>1. separated single turn loops ?   What diameter,   what separation ?
>
>2. multiple independent isolated turns on a common diameter ?   what
>diameter

Hi Stan:

My loops are about 100' perimeter - rectangular.  30 feet horizontal 
by 20 feet vertical.  The bottom conductor is about 6' above 
ground.  I have a NS loop and an EW loop - the NS one uses the same 
tree for two of its supports as the EW one, so 3 trees forming a 90 
degree (approx) angle at the middle.  My loops aren't exactly equal 
in size and they aren't exactly orthogonal, so you can't just add the 
inductances when connecting them in series.  The wire is something I 
found years ago at a surplus dealer in St. Jerome, QC.  It has a 
great number of strands all twisted together (individual strands not 
insulated) and the overall diameter is about 5/16 inch.  Wire has a 
very tough insulation - I've used this stuff for about 20 years now 
out in the sun and ice with no sign of deterioration.  The loops are 
supported by bakelite insulators at 4 corners; each corner is 
attached to its tree support with one of those stretchy black rubber 
tie-downs the truckers use.  So when the wind blows the loops 
hopefully stay up.  I've had to replace the black rubber tie-downs 
many times: after about 2 years they disintegrate - but never had the 
conductor break yet.  Feed each loop at mid-point of bottom run, use 
450-ohm ladder lines to a point where there is another bakelite 
connection block.  I label the EW loop connections as A,B and the NS 
loop connections as C,D.  That lets me use either loop standalone, or 
by connecting them in series I can select one of 2 possible 45-degree 
lobes: NE-SW or NW-SE.  If you visualize a signal coming in from the 
SE for instance, the magnetic component will be horizontal and 
perpendicular to the line of arrival.  You can apply the right-hand 
rule in your head to figure out the correct series connection so the 
voltages in both loops reinforce for the incoming direction you 
prefer and cancel for the opposite.  I use a short jumper line with 
eyelets crimped onto the cable to make the series connection.  The 
remaining 2 terminals on the center bakelite block are the feed point 
connection.  Everything has to be low contact resistance back to the 
preamp box where I add more series inductance and tune to 
resonance.  Currently, I'm using a pre-amp (instrumentation amp made 
from 3 sections of a TL084, 4th section buffers VCC/2) to avoid 
loading the Q and drive the long cable back to the shack.  The 
arrangement worked quite well for years without a preamp but a higher 
Q helps pull in VLF stuff like SAQ.  With one of 2 switch-selected 
inductance supplements, I can tune both VLF and LF bands using a 16 
nF variable cap. The capacitor box consists of 4 fixed caps I can 
switch in (8, 4, 2, 1 nF) plus one 1000+ pF variable.  There is an 
isolating transformer at the preamp and one at the other end of the 
buried cable where it enters the house, so I use a 12-V gel cell to 
run the preamp out in the woods.  Cable is cheap twisted pair, about 
100 ohms impedance.  I started out laying it on the ground but after 
a few years it buried itself, hi!  So far the local critters haven't 
chewed through it.  The weak point of this system is too many 
connections.  About once a year I have to undo all the connections, 
clean them and re-make them.  Things corrode when exposed to the elements.

73,
Bill VE2IQ