Re: [IRCA] IRCA Loop update

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> Yesterday I built a 5-foot diameter square copper pipe loop, using 1/2
inch
> copper pipe (two 10 foot sections), and an FT-140A-J high-permeability
> toroid.
(snip)

> It takes a LOT of heat to solder the elbows to the pipe ends. I started
out
> with the standard propane torch, but my cylinder used up within 5
minutes--I
> hadn't used the torch in years.

Hmm.  I used a common propane torch even on the 1" model.  Clean the copper
with emery or sandpaper and use flux.  The solder I used is the Oatey lead
free 5% silver stuff Home Depot sells.  Put the flame mostly on the joint
and let it suck the solder in.

> My thinking on the toroid transformer was the pipe resistance was in the
> range of 0.1 ohms; a match to 50 ohms coax would be the square root of
> 50/0.1 or 500, which rounded off gave a convenient 22 turns for the
> secondary winding on the toroid. I used #24 gauge enamel wire, with a BNC
> connector attached.

Ah.  There's a problem.  The second loop I built used 24 turns of #16.  Had
very little output voltage.  I unwound it down to 6 turns and it was good.
Later I tried four turns of #16 and it was even better.  I have not tried
either three or five turns to see where the optimum point is.  Rewind the
output link to four turns of #16 or heavier wire and it'll make a big
difference.  And no, I have no idea why.  All I know is that it just works.

> So, for my initial experiment with a 5 foot copper loop, frankly, I am
quite
> unimpressed--at least compared to what I can hear with my wire antennas. I
> bought enough extra pipe and elbows to make a 10 foot diameter loop, but
> based on this first test, I'm not sure I'll build it. It will be a very
huge
> affair and won't be easy to suspend and rotate.

Try again with the same output link I use.  I have plenty of signal into my
R8B even without a preamp.

Craig Healy
Providence, RI


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