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Re: [TowerTalk] Stacking tribanders

To: "Edward Sylvester" <>,<>
Subject: Re: [TowerTalk] Stacking tribanders
From: "Clay Curtiss" <>
Date: Sun, 30 Jul 2006 17:58:27 -0700
List-post: <>
----- Original Message ----- 
From: "Edward Sylvester" <>
To: <>
Sent: Sunday, July 30, 2006 2:56 PM
Subject: Re: [TowerTalk] Stacking tribanders

Here's what I've come up with.  There is no ideal separation distance, as 
we're dealing with multiple bands.  The emphasis in my case will be 20m. 
I'm will be using 2 antennas.

  The bottom antenna will be a Steppir 3 ele 6-20m antenna at 35-40'.  The 
top antenna will a Steppir 4 ele 6-20m antenna at 70'.  These will be fed 
through the Array Solutions Stackmaster II, thereby eliminating the need for 
precisely cut feedlines, so long as they're the same length.

  I will be using a crank up Hygain HG-70HD.  How does this sound? 
Feasible??  Objections welcome!

  Ed NI6S

Hi Ed,
I've done a lot of models for the folks at SteppIR and have done extensive 
modeling of stacked SteppIRs.  I think you may be disappointed with your 
current plan.  My models show that 4 over 3 SteppIRs at heights below 90' 
will only give you about 1.7 dB improvement over the single 4 element.  Most 
of my models have been based on placing the top antenna at 90', and I'd 
actually expect the stacking performance to decrease as you move the stack 
closer to the ground.  Also, the driven elements on the two antennas are not 
vertically aligned, so you'll need to account for that by adding a phase 
delay (something like 60 degrees if I remember correctly) to the 3 element 
antenna whose DE is much closer to the center of the antenna.  The total 
gain for the 4 over 3 stack is only about 0.5 dB better than a 3 over 3 
stack.  After a lot of analysis, I've decided that 3 over 3 at 90'/55' (35' 
spacing) gives the best performance and flexibility for my setup (my goals 
seem to be about the same as yours).  This spacing seems to work well for 
20-10M and actually works ok on 6m also, although there are a couple of high 
angle lobes present since the spacing is so large.  I should also mention 
that the 3 over 3 stack outperforms the single 4 element by about 1 db when 
the antennas are fed in phase and gives you the take off angle flexibility 
that you don't get with the single antenna.  The 3 over 3 stack also has the 
benefit or reducing the wind loading at the top of the tower by 3.6 sq ft. 
when compared with a 4 over 3 stack.

In my models, I've also noticed that the F/R suffers when the antennas are 
stacked.  However, I've been able to re-optimize the element lengths based 
on the stacking distance and height above ground and can get F/R numbers 
that meet or exceed those of a single antenna.  In some cases, the change in 
the reflector and director lengths are significant for best stacked 

Of course local terrain will impact your results, so YMMV.

Clay W7CE

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