At 11:58 AM 2005-12-21, Kevin, N8IQ wrote:
I've been thinking about what kind of antenna to put up. With my height and
deed restrictions, I'm quite limited. I've thought about putting up a
horizontal loop antenna. Basically I was planning to run some enameled
magnet wire around the perimeter of the roof (I have no plans on running
more than 10 watts). The wire would lay under the shingles so it can't be
seen. The antenna will be 1 WL long on 80 meters. I'll run coax down to the
K2 + ATU.
This is similar to "The Loop Skywire" described in the November 1985 issue
of QST. Anyone have experience (or see a problem) with this antenna?
Kevin,
Just be sure that the high voltage points on the antenna are well
insulated from your shingles. The voltages are maximum at 1/4
wavelength away from point on the loop which is opposite the
feedpoint (and every 1/2 wl from those points on 40m and higher
bands). Even with 10 watts, you could see about 200 volts (rms) RF present.
When the shingles are damp, you may see a bit of detuning from
increased capacitive loading (and a little extra loss).
I used a 30 foot high horizontal loop (1 wl on 80m) at my Seattle QTH
and was quite pleased with its performance on 80m-10m. One side ran
closely parallel to the aluminum gutter above the second story. The
remainder of the loop was stretched to trees across a small
creek. Feed was through a short length of 300 ohm line and a
link-coupled balanced tuner.
The loop was originally made from stealth #26 magnet wire, which was
fine for RF (100 watts), but was often trashed by falling tree
branches. It was later upgraded to bare #22 and the mechanical
problems were nearly nonexistent (and it was still nearly
invisible). When I started to get ice buildup, I connected the loop
to a low voltage DC supply which warmed the wire enough to melt the ice off.
ARL 61,
Terry N6RY
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