[Towertalk] OCF Longwire with moveable feed point

[Terry O'Neill]

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 3.5
wavelengths on 40 meters (about 475 feet @ 7.2mhz per
the Antenna book) would be feasable.

What if one was to erect a folded doublet, 455 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, 455 feet is
approximately 7 wl, which would theoretically yield about
5.5 dbd. The gain would increase with frequency to about
8 dbd @ 10 meters.

Per the Antenna Book, take-off angle also decreases with
wavelength, so it should be a good DX antenna.

It would seem to be a cheap alternative to a beam if a
person had the room.

Has anyone built and or modeled this antenna? If so, I
would be curious as to the results.