[IRCA] Antenna test

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

Recently I had the opportunity to use a commercially-made H-Field shielded
loop antenna.  What I did was set it outside my truck and parallel to one of
the copper tube loops I have in the back of my Chevy Blazer.  The antennas
were both connected to an Alpha-Delta 4 position switch inside, and then to
the Palstar R30CC.

Tuning through the AM band, I stopped at every signal of notable level.  I
considered stations in Boston and NYC to be appropriate.  S-Meter readings
were compared.  Since the antennas were identically oriented, the figure-8
patterns were the same.

In every instance the copper tube loop had a higher signal level from bottom
to top of the band.  In some cases stations inaudible on the commercial loop
were listenable on the copper tube loop.  There were no stations heard on
the commercial antenna better than the copper loop.  The commercial one was
outside the truck while the copper loop was inside the bed with a fiberglass
roof which was probably a slight advantage for the commercial one.

Considering that the overall parts cost of the copper loop was maybe fifty
bucks tops, plus an hour's work, I think it's a much better deal.  The parts
list is one 10' length of 3/4" copper plumbing tube, four 90 degree elbows,
an Amidon FT-240-77 toroid, a few feet of #14 THHN stranded electrical wire,
and an SO239 jack.  Not much to it and quite simple to build.

This particular loop is untuned broadband, just as is the commercial one.
If a tuned loop were desired, it would be simple to put a 40 turn winding
(plus or minus some turns) on the toroid core and add a variable capacitor.

I will be happy to say just what the commercial antenna is, though I'd
rather not post it publicly.  Drop me a note if you are curious and I'll
send a link to the sales web site for it.

I'd always wondered how well a moderately expensive commercial test antenna
would do in a DX situation.  Now I know, and I won't be spending any money
for one.  Another question answered, and I'm happy.

Craig Healy
Providence, RI


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