I do have older versions of AO and EZNEC so perhaps I'll
give them a try to see how things look. My guys wires
pretty much dictate allowable stacking distance if I want to
be able to rotate the lower beam. I'll probably be stuck
with 100' and 50' which looks like a decent arrangement to
be stuck with!
Your comment brings up a good question, as a general rule,
does stacking yagis typically result in a lower overall F/B
of the array? I wouldn't think so. If done correctly array
gain goes up and I expect array F/B to also improve.
73, Bob K6ZZ
----- Original Message Follows -----
Subject: Re: [TowerTalk] Stacking 204BA's
Date: Fri, 9 Mar 2007 17:19:15 -0500
> 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.
> John KK9A
> To: email@example.com
> Subject: Re: [TowerTalk] Stacking 204BA's
> From: "Bob Selbrede, K6ZZ"
> Date: Wed, 07 Mar 2007 20:06:29 -0800
> List-post: <mailto:firstname.lastname@example.org>
> 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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