Re: [IRCA] IRCA Loop update

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> Well, the outer diameter of a conductor is really what gives it the
capacity
> to handle current, due to the "skin effect."   I wonder if the collective
> outer diameter surface area of Craig's cooper pipe loop is sufficient to
> overcome the collective outer diameter surface area of all of the wires in
a
> wire loop.  Mathematically I can see how it could be the case.  Maybe the
RF
> capture success is directly related to the surface area of the antenna.

It may be.  There was no math or thought given to the design of this puppy.
I saw the one on the Stormwise site and thought it looked interesting.
That, and the fact that I had a bag of ferrite toroids and the plumbing
supply is just up the street.

> The ability to conduct current, and the ability to snag microvolts from
the
> ether, are undoubtedly related in some way.  To take maximum advantage of
> surface area, maybe we could DX with a big brass sphere behind a curved,
> rotatable "nulling" shield.

That has been tried using a barrel and some screen.  No go.  It takes a loop
to act as a current probe.

However, a shielded loop is possible.  In FM broadcast a common transmission
line is a 3 1/8" coax in both rigid and flex.  I'm trying to round up a 12'
length of the flex stuff.  It can be bent in a loop and the center
conductors put through the toroid and soldered together.  Then the outer
shield can be grounded on one end.  It'll be a unwieldy thing, but will
pretty much be a shielded version of the last 1" loop I built.  It may drop
the noise pickup down a bit, though it really is good now.

I continue to be amazed at the wideband ability of this thing.  I put the
two foot version in my truck yesterday.  Just bungee corded it to the spare
tire.  I have a 1988 K5 full size Chevy Blazer.  This has a short pickup bed
with a fiberglass cap over it.  RF can get in.  The loop picks up no
ignition noise at all.  CBA-1070 was perfectly readable at 3pm yesterday
afternoon.  Normally weaker stations like 1510 Boston and 580 Worcester were
easily listenable.  On FM it could get maybe 80% of what I can get with the
roof mounted mag mount whip.  That was really surprising.  Even SW in the
49m band was good.  Nothing heard on LW, but it was all external line noise
with no ignition racket or alternator whine.

There was a directional nulling effect noted, but it was not a real problem.
It may turn out to be an asset at times.

Priced some Amidon cores.  The FT-240-77 core is $9 each and the larger
FT-290-77 is $18.  I will buy some of each for comparison.  Once I get the
larger core I will make a loop out of 1 1/2" tube to see if that makes any
difference.  There is probably a point of diminishing returns.

Craig Healy
Providence, RI


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