Re: [IRCA] Dual feed loop

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

> What is the configuration of the indoor test loop that you're
> evaluating? I take it that this is an untuned loop(s)?
>
> I don't have room for anything substantial outdoors at my current
> location and have been using various indoor NRC-type loops exclusively.
> I do have an ANC-4 phaser and might possibly be able to make use of it
> on something moderate in size, usable indoors.

http://www.chowdanet.com/Photos/dualfeedloop.jpg

A picture is worth a thousand words, or at least a few minutes work. (grin)
This picture shows the loop which is about 32" on a side.  There are two
pickups, each centered in the top or bottom horizontal sides.  It's
broadband with no tuning.  FWIW, I did add a tuning winding to one of the
test loops, and it did sharpen it up somewhat, but not enough to be worth
the added work.

Each pickup is an Amidon FT-240-77 toroid with four turns on #16 wire.  As
the wire leaves the toroid, it's twisted and run through two Radio Shack
clip-on ferrite chokes.  Then the wires are soldered to an SO-239 jack.
Dead simple and takes maybe 20 minutes to build.

The loop itself is just a 10' length of 1" copper plumbing tubing cut into
quarters.  It's then soldered together using common 90° elbows.  The pickups
are slipped on first, of course.

>From there I made up a quick clamp-type base to support it.  The base took
more time to build than the loop did. Two lengths of coax go to the phaser.
These do require a preamp, and I use the DX Engineering version after the
phaser.

At the moment I'm using this in my upstairs computer room.  Noisy, and
there's wiring in the ceiling that no doubt affects things.

As to size, I have made these from ten foot on a side down to maybe two
foot.  The signal strength does vary, but not as much as I would have
thought.  It may be that even a one foot square loop would work fine. I do
think that the larger tubing works better than even heavy wire would.

Craig Healy
Providence, RI


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