I was reading an old 73 Magazine, (May, 69') when I saw an article
discussing Off Center Fed longwires. The article
examines directivity pattern of a 3.5 wavelength longwire. Article shows
how the radtiation pattern changes depending on
where the feed line is placed along the length of the antenna to achieve
a steerable pattern. This article was written before
antenna modeling programs were invented and I assume the author's
(W2EEY) results were experimental, although he doesn't
say.
Per the ARRL Antenna book, a 3.5 wl longwire has about 3db gain over a
dipole.
I have a long narrow lot with several tall trees where 4 wavelengths
on 40 meters (about 550 feet @ 7.2mhz per the
Antenna book) would be feasable.
What if one was to erect a folded doublet, 550 long, fed with open wire
to a tuner ? Further, what if one were to arrange the
wire of the folded doublet in a continuous loop around pulleys, so that
you could move the feedpoint where you wanted it along
the length of the doublet.
The result should be a 3 dbd gain antenna (on 40) with steerable
pattern. Further, on 20 meters, 550 feet is approximately 8 wl,
which would theoretically yield about 6 dbd. The gain would increase
with frequency to about 8dbd @ 10 meters.
Per the Antenna Book, take-off angle decreases with length, so
it should be a good DX antenna on 14 - 28 mhz & possibly 10mhz.
It would seem to be a cheap alternative to a beam if a person had the
room.
Has anyone built this antenna? I do not have modeling software so I would be
curious as to the modeled performance @ various heights say 30 - 50 feet.
Is antenna height as important with long wires as it is with dipoles & yagis in
determining take-off angle? How would it behave on 160 & 80?
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