[TowerTalk] Stacking Tribanders was: Re: Stacking 204BA's

[Pete Smith]

A few years ago I did a lot of computer modeling in trying to figure out the best spacing for a 2-high stack of C-3E tribanders.  In the process I discovered a couple of things that may be relevant:

-- compromise spacing is just that, and even over a 2:1 frequency range there really is no decent 3-band compromise, so the problem with a 2-stack on MonstIRs is truly compounded.  I would up compromising between 20 and 15.

-- there are some quirky sweet spots for F/B ratio.  For example, a 2-high stack of C-3Es on 20 has F/B of only about 11-12 dB, but at 36 foot spacing, my models show that the stack exhibits 26 dB F/B over a relatively narrow frequency range at the bottom end of the band.  I was tempted to move my lower yagi from its original 28-foot compromise spacing to 36 feet, at least for the remainder of the sunspot minimum, but the modeling doesn't show a comparable "sweet spot" for stacking gain.  I often find that low F/B isn't *that* big a handicap, and it would have been a lot of hard work, so I left things alone.

73, Pete N4ZR

 At 09:27 PM 3/9/2007, Cqtestk4xs at aol.com wrote:
> 
>In a message dated 3/10/2007 2:22:06 A.M. Greenwich Standard Time,  
>k6zz at ccis.com writes:
>
>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.
>
>
>~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
>I found that my 2 high and 4 high stacks suffered in the F/B area.   However, 
>my QTH was in FL so F/B was not much of a problem, since the back was  
>usually Africa, VK/ZL and South America....not all that much of a problem for  
>signals off back of a stack, and sometimes very handy for a juicy mult to call  in. 
> 
> 
>The same will be true in KH6 with my new station...not much off the back  
>when facing JA, W or EU.
> 
>Bill K4XS/KH7XS
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