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Re: [TowerTalk] Stacking tribanders

To: "Edward Sylvester" <>,<>
Subject: Re: [TowerTalk] Stacking tribanders
From: "W7CE" <>
Date: Sun, 30 Jul 2006 21:20:42 -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!
>  73,
>  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. 
 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 
 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 
 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 
 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 
 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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