Re: [IRCA] IRCA Loop update

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> > I have to tell you, I don't think I will ever make a wire loop again.
The
> > untuned copper loop works better than any tuned wire loop I've ever made
or
> > used.
>
> I am very puzzled by this.  It seems to me that a copper tubing loop would
> just look like a very thick piece of wire about 8 feet long, or in the
case
> of the larger loop you built about 40 feet long.  I learned to make loops
> from Ralph, and the wire loops I built have between 95 and 120 feet of
wire.
> It seems to me that all of that extra wire, especially when compared to
the
> smaller of the loops you built, would have a much larger "capture area" so
to
> speak, when compared to 8 feet of thick wire.

I don't claim to understand exactly how this works, only that it certainly
has for me.  The best thing I can suggest is to buy a ferrite toroid and
make a visit to a plumbing supply house for the tubing.  I would be very
happy to see someone else confirm this.  And, I will be bringing a few of
these to Chris Black's GTG on the 19th.  Let others try it.

I have two identical five foot loops and bases to put outside.  The idea is
to orient the loops so they both null one pest but are spaced at least 100'
apart and in line.  Then, use a phaser to either deepen the null or null a
second station.  Since these are untuned, it's quite easy.

> The stronger the wave, or the larger the coil of wire, the more current
> should be induced to flow.  So it puzzles me that the 8 foot copper tube
> works as well for you as 90+ feet of wire.

One thing to consider is skin effect.  At RF current tends to flow on the
surface of a conductor.  A 1" copper tube has the same RF resistance as a
solid bar of that diameter.  That's why AM and especially FM coax is
tubular.

> In some kinds of antennas, like an ordinary dipole, for instance, a wire
that
> is very thick can add some usable band width to the antenna.  That is why
> they used to build those "cage" dipoles that were several parallel wires,
> held apart in a kind of circle by spreaders, to form an artificial "thick"
> wire.

A dipole is a tuned antenna.  This loop seems to function as an untuned
current probe.  It has been effective from below the LW broadcast band up
through at least the 40m ham band.  I have even heard CB on it.  As an
inside or ground mount antenna, it's less effective as you head up towards
VHF.

Find a toroid, build one, and let us know.  These take me maybe an hour at
most to build.

Craig Healy
Providence, RI


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