JB - the pickup loop should not be
shielded....just use a piece of wire (any guage...no need for
#12)... that the main loop is made from. A single turn, connected across
your coax feedline.
Steve / VE7SL
Hello LF Group,
I've finally finished the construction of my LF
loop and I appear to have a
problem with it regarding the connection to the
receiver. The loop itself
is in the form of an octagon, with an overall
diameter of 10.5 feet, and it
consists of 15 turns of number 12 THHN stranded
wire. The spacing of
the turns is 0.25 inch and the tuning is done
with a 3 gang, 400 pF. per
section, variable capacitor with all sections
connected in parallel.
Checking with a weak signal source, the tuning
range is roughly 100 to
300 kHz. This agrees with Reg's program for
multi-turn loop antennas.
A portable radio covering the LF band really
comes to life when I bring
it close to the loop, and by turning the
loop in azimuth I can peak the
signals and/or null out noise. This would
indicate that it is working as
I would expect.
The problem is with the pickup loop, which
is of the classical shielded
construction as described in many antenna
books. Mine is made from
RG-213 coax and it's positioned
roughly six inches inside of the main
loop windings, but in the same plane. The
station receiver, a TS-440S,
gets better reception of LF signals when it's
connected to my 40 meter
delta loop than it does with the LF loop!!
I know the feedline is OK, as
I've checked it with an MFJ-259 antenna
bridge and a 50 ohm load at
the antenna
end.
The one suspicion I do have is that the cable
clamps I've used to hold
the pickup loop to the frame are made of metal
and are shaped like a
capital letter P. I'm wondering if these
look like shorted turns to the
pickup loop and are attenuating the signal?
Before I get out my big
stepladder and replace them, I thought I'd ask
the opinions of those
of you who have
gone before me. Any/all suggestions are welcome.
73, J.B. Weazle McCreath, VE3EAR -
VE3WZL
