[IRCA] IRCA Loop update 4

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

I had some time on this rainy Saturday to do some further work on the loop
project.  This particular one is made of one inch copper tubing, five feet
on a side.  Square shape using normal 90° plumbing elbows on the corners.

A winding of about 36 turns of #22 teflon wire was wound on the toroid and
soldered to the terminals of a common 15-365pf air variable tuning
capacitor.  The output winding was brought down to four turns from the
previous six.  It seemed to be overcoupled and was lowering the Q so that
tuning wasn't very good.  The toroid is still slipped over the bottom center
of the vertically mounted copper square.

The tuning brought the loop output up a couple of S-units.  It is to the
point where there is almost too much level into the R8B.  Nulling stations
seems somewhat better, though not greatly different than before.  This seems
to act much like a seven foot spiral loop I had some years ago.  Good
nulling, and good output.  The performance continues to exceed my
expectations.

This has a number of advantages over the more common wire-wound loop.
First, it's a bunch quicker and easier to build.  Second, it's much less
fragile.  Third, it can be used sans capacitor as an untuned loop over a
very wide frequency range.  Fourth, it can be easily waterproofed for
outside use on a rotor - without the tuning, of course.  Fifth, it is not
very sensitive to hand capacitance.  I can grab the copper, turn the thing
to null, and the null is just about the same when I take my hand off it.
The null would change in the spiral loop even if my hand got close to it.
This is a lot better.

Next part of the project is to design up a good azimuth/elevation mount for
it.  I haven't figured exactly how I want to do this yet.  I want something
strong, clean, and even elegant.  The Muse hasn't struck yet..

I also want to build a yet smaller version, perhaps 2.5 feet on a side.
This can be built out of one ten foot length of tubing, and four elbows.
Cheap.

I'll try to take some pictures tomorrow when the light is better.

Craig Healy
Providence, RI


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