[IRCA] Copper loop update 2

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

I have had a chance to do some further work with the copper loop today.  I
set it up with a temporary mount of a wood stake into the ground.  Here is a
picture of the setup:  http://www.chowdanet.com/irca_loop.gif

The feed is still the same, and I have a picture of it to help clarify:
http://www.chowdanet.com/irca_feed.gif

My goal today was to see just how well it could null.  Bear in mind that
this is untuned.  No tuner on the loop itself, nor is there one at the
receiver end.  It's simply loop - toroid - RG-8 coax - receiver.  I chose
local WPRO-630 to null, as they block a couple of possible semi-locals.  I
was able to reduce WPRO down to S-2-3 from S9+30.  Good enough daytime to
bring them down into the noise.  Adjacent on 620 was not there.  640 near
Springfield, MA was S-5 or so, and perfectly listenable.  Normally the WPRO
splatter makes it impossible.  Nulling was fussy, but no more so than any
other loop antenna.  The orientation also weakens many Boston stations.
WSRO-650 is not audible at all, for example.

One very interesting and unexpected thing I found was that the toroid can be
slid along the bottom tube to fine-tune the null.  Even an inch or so of
movement makes a noticeable change.  It nulls best within a couple feet of
the center.

The next work will be a real elevation/azimuth mount, and possibly turned
with a rotor.  I don't have anything right now to do the elevation part.

It's likely that having the botton tube right on the ground has an effect.
When I make a mount, it will be to orient it in a diamond configuration with
all tubes being 45° from horizontal one way or the other.

So far I am very pleased with the performance, even without the preamp which
hasn't arrived yet.  I've heard a number of uncommon and difficult stations.

Craig Healy
Providence, RI




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