[IRCA] Loop update 12-16

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

I've done more work on the copper loop project.  The initial versions simply
had the #16 wire wound through the toroid and twisted for a few inches, then
soldered to the SO-239 jack.  I had a couple of ferrite chokes, so as a test
I made the twisted wire pigtail longer and looped it through the choke to
isolate the common mode currents.  These were used in the truck and I
noticed electrical noise was less of a problem.

The latest loop is 2 1/2' on a side of 1" diameter "M" tubing.  The toroid
is an Amidon FT-240-77.  I built it first without the choke and used it for
a week or so.  Then, I stopped by Radio Shack and picked up a couple of the
clip-on chokes.  Three turns of the twisted pigtail were wound through two
of the chokes.  Noise dropped noticeably.

Here's a shot of the feed of the current model:
http://www.am-dx.com/Graphics/loop_feed_choke.jpg

Nulling is quite good in the house, and would likely be better away from
metal and house wiring.

I have removed the outside antennas from my truck, and now rely entirely on
the two cross-mounted loops in the back.  AM performance is significantly
better, and FM is reasonable, though not optimal.

Next phase will be to make two 12"x24" loops to cross-mount on a mast to
mount outside the truck in a permanent fashion.  I'll see if performance is
improved by moving them outside the fiberglass bed cover.

Another project is to make a 4' x 10' version in the form of a small EWE.  I
have some 1/2" fiberglass rod to put in the middle of the 4' verticals.  I
also have some conductive plastic pots, and a 9:1 transformer made for it.
We'll see if a cardiod pattern is possible on that small an antenna.

Craig Healy
Providence, RI




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