[TowerTalk] Scaled Antenna

[Michael Tope]

Ron,

How many wavelengths at 18 MHz did you raise the ground system?

Mike, W4EF..........

----- Original Message -----
From: Ron <majrabsr@rconnect.com>
To: <towertalk@contesting.com>
Sent: Friday, April 21, 2000 6:35 AM
Subject: [TowerTalk] Scaled Antenna


>
> Hi guys,
>
> I have completed the first part of the scaled tower tests. The results
> contained a big surprise, at least to me.
>
> Since my tests were on the 17M band and I wanted everything to be as
> realistic as possible, I began by constructing a scale model (actually two
> of them) of Rohn 20 tower using 1/8" galvanized pipe spaced 1-1/8" on
> center. This section was 6 feet tall. 3 feet of ¼" galvanized pipe was
> attached to the top of the miniature tower and a top hat with a diameter
of
> 7-1/2" was used to resonate the model at 18.12 MHz. ¼" fiberglass rod was
> used to insulate the antenna from ground, with a space of 2".
>
> I set the antenna up on a 190' x 170' area near my pond, which stays
> somewhat damp (according to previous owner). This is where I plan to
install
> the 160M antennas. 60 radials, each 13 feet long, equally spaced at 6
> degrees were installed at the test site. The antenna was fed with 70-ohm
> coax through a shunt feed. An MFJ 259B was used to adjust the match. One
> watt of power was fed through a step attenuator to the antenna under test
> and readings were taken with a F/S meter. Antenna pattern was clean and
> quite circular.
>
> Next, I raised the antenna and used a counterpoise system. This is where
the
> surprise came. It only took 8 radials to provide the same F/S as the 60
> ground-mounted radials! F/S with 60 radials was approximately 135% higher
> than when the radials were ground mounted.
>
> Is this a surprise to anyone but me? Has anyone else observed the same
> results regarding a counterpoise?
>
> Next step is phasing the two antennas.
>
> Thanks,
> Ron, KA9ALC
>
>
>
>
>
>
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