It's not surprising that you notice some F/B degradation. If F/B ratio is
important to you, you can minimize the degradation by increasing your
spacing distance. Do you have AO? If so, you can optimize your stack using
that. You can also use AO to check for interaction with any other antennas
on your property, which is a feature that I find very useful.
73,
John KK9A
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Stacking 204BA's
From: "Bob Selbrede, K6ZZ"
Date: Wed, 07 Mar 2007 20:06:29 -0800
List-post: <mailto:towertalk@contesting.com>
I'm not sure if my version of YO (YO5) will do the job as
described below. I've done the HFTA analysis and the
elevation diversity attainable with stacked 20M beams at
100' and 50' is pretty substantial regardless of the type of
antenna used (204BA, 205CA, KLM 20M6, etc). For all
practical purposes my local terrain is flat (+/- 100') for
3-4 miles in every direction.
Therefore, I'm down to how to optimize the 204BA's for this
application. YO5 allows the user to model yagis
individually over real ground or in free space. Both the
W6QHS dimensions and the N6BV version (BV204CA) look pretty
good individually. However, when you model a stack of two
yagis with YO5 it only does it in free space. When doing so
the results (if believable) do not look so hot for the N6BV
variant. The F/B goes from better than 20 dB across the
band to around 12 dB at the lower part of the band. The
W6QHS and original Hy-Gain dimensions do not appear to be as
bad.
73, Bob K6ZZ
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