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Bob Schreibmaier · September 6th 07, 01:34 AM posted to rec.radio.amateur.antenna

In article ,
says...

I thought I'd post the results of my recent little project to put up a
Carolina Windom for 80/40/20.

Didn't work very well. :-(

At least, not yet. ;-)

I cut it for 3.6 MHz, and according to everything I read that should give
decent performance on or about 7.2, 14.4, and 28.8 MHz.

Instead, I got 3.6 MHz (as expected), then I got about 6.6 and about 14.9.

I followed the instructions I found in one website article that said to
cut the legs for 37.8 percent and 62.2 percent.

Other articles I've read say to cut for 1/3 and 2/3 of a half wavelength,
i.e. feed the antenna 1/3 of the way from one end.

Since I'm a high precision sort of a dude ;-), I figured 37.8 and 62.2
were more precise than 1/3 and 2/3, so I tried them.

Like I said ... works well on 3.6 (and most of the rest of the 80 meter
band) but not anywhere else.

It is built with a W2AU balun (4:1), 22 feet of RG-8X, an MFJ "line
isolator" (1:1 current-type unun), then about 25 feet of RG-8X to the
shack.

I guess I'll have to go back up there next nice day and try the 1/3 2/3
way.

The 14.9 MHz sounds about right, but the 6.6 MHz sounds
very weird. I would have believed 7.6. In general, the
40-meter resonance point will not be exactly twice what
it was on 80 meters, nor will the 20-meter resonance point
be exactly four times what it was on 80 meters. Generally,
it will be higher in frequency.

I have had good success in the past using the 1/3 and 2/3
leg lengths with a Spiro 4:1 balun and a bead balun right
at the feed point. However, if you really want this to
work on 40 and 20 meters, you will want to make your antenna
longer than you have.

I used legs of 45 and 90 feet. The SWR was about 1.0 at
3.5 MHz and 1.3 at 3.6 MHz. Actually, it didn't reach 2.0
until about 3.75 MHz. Lowest SWR on 40 meters was at 7.2 MHz
at about 1.0 and was low across the band. The lowest SWR on
20 meters was at 14.35 MHz at about 1.0, but was 1.8 at the
bottom of the band. By the way, it didn't look nearly so good
on 10 meters, where the lowest SWR was 1.8 and quickly rose
to over 2 at 200 kHz either side of 28.6 MHz.

Good luck with whatever you try.

73,
Bob
K3PH