I have used the 4nec2 program with good results modeling my VHF stack.
Its interface is quite good and the price is free.
Its also pretty good for modeling HF antennas although you may have to
play with the ground impedance parameters for your location.
73 Erich
N6FD DM15dp
On 12/29/2013 11:06 AM, john@kk9a.com wrote:
I have YO, AO and EZNEC+. I would recommend purchasing
http://www.eznec.com/ . The 2m and 6m beams should be pretty easy to model,
the X7 is not. I suspect that your system will work fine as proposed but it
is still nice to model and see what is happening. I modeled every antenna
on my tower trying to minimize interaction however there are always
compromises.
John KK9A
To:<TowerTalk@contesting.com>
Subject:Re: [TowerTalk] HF-VHF-VHF Stacked Yagi's on Single Mast
From:"N8GLS" <n8gls@arrl.net>
Reply-to:n8gls@arrl.net
Date:Sat, 28 Dec 2013 20:46:52 -0500
Thanks All for the comments.
K5GO (Stan), Oops, yes, the longest element on the 6m beam is 10 Ft, not 5
Ft. Yes, I am aware of the differences of stacking same band antennas
versus just stacking different band antennas on a single mast. Please see
my general comments below.
KK9A (John), Yes, I would like more mast nested inside the tower as well.
When I got the 1026 DOM mast I said to myself, &*%$#, that?s heavy, and
LONG. That?s why I keep putting the 6m beam at the top, with its paltry 2.2
Sq Ft of wind area, albeit at 12 Ft atop the mast.
W1DYJ (Larry), thanks for re-directing me back to that very good article. I
did read it some time ago along with several others and many many comments
on various other formulas and/or rules of thumb, most of which aren?t much
better than a guess....which is why I come to the pool of experts here !!
All aside, it seemed to me that if I centered everything around the highest
frequency band (2M in this case) and try to keep everything out of its
aperture then all should be good with the world. With the 6m beam at approx
5 Ft above and the HF tribander at 5 Ft below, both are just inches inside
the aperture of the 2M beam, but it isn?t seeing much of that metal as there
are few elements and they are very wide spaced. The HF tribander is
completely outside the aperture of the 6m beam, yes the 2m beam is way
inside the aperture of the 6m beam but with its large aperture coupled with
the "small" elements of the 2m beam I didn?t think that it would result in
any major loss in gain. I can't guess on the effects it may have on SWR.
Several of you mentioned modeling the stack to get a better idea, what
software are you all using??
Brad, N8GLS
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