[Antennas] OCF Long-wire with movable feed point

Sun, 21 Apr 2002 08:45:22 -0500

Hi Terry and list readers,

The article published in the November 2001 issue of CQ describes just what 
you are proposing.  The Motorized Clothesline Antenna.  Check it out.  A 
novel and interesting concept.

73, Jim, wd4air

>From: Terry O'Neill <[email protected]>
>To: [email protected]
>Subject: [Antennas] OCF Long-wire with movable feed point
>Date: Fri, 19 Apr 2002 21:46:51 -0400
>
>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
>like this:
>
>xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>
>x
>x
>x    x
>x
>x
>x    x                     x
>x
>x    x
>xxxxxxxxxxxxxxxxxxxxxxxxxx
>xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>                          x            x
>
>                          x            x
>
>                          x            x
>
>                          x            x
>
>                          x            x
>
>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.
>
>
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>
>  Match
>  Box
>
>  Rig
>
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>
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