This is true, always has been. Typically a commercial yagi is designed for
single use, far and away the most common use. Stacking three plus elements
does produce the kinds of improvements proffered for stacks. The
difference in a stack of single use design and a stack designed as a stack,
probably cannot be detected by the other end, with other issues, like
feedline loss, or corrosion issues a far greater villain. Further, even in
stacks, a lot of the use is still lower only or upper only, STILL
vindicating design for single use.
Stack interaction is VERY evident if you stack two element beams, as their
interaction is huge, rendering two element stacks not worth the effort.
The free space pattern of a yagi needs have an over/under null to stack
"well". This is very easy to model.
73, Guy.
On Sat, Feb 25, 2012 at 5:21 PM, George Dubovsky <n4ua.va@gmail.com> wrote:
> I am trying to optimize a pair of HyGain 204BA for use in a stack. I am
> using YO v7.61 and, mostly, I think I know what I'm doing at a basic level
> ;-)
>
> I intend to mount one at 70' and one at 110' (that seems to work in HFTA
> for this location), but that's not my problem. I can optimize an antenna at
> either height, and I can design a new Beta match. But when you select the
> stacking feature of YO (using 40'), the element spacing seems to want to be
> different and the matching of course changes. What that seems to be telling
> me is that when I select upper, lower or both using a stack-match only one
> condition is going to be correct, and the others will be a compromise.
>
> It can't be this tough - I feel that I am mis-interpreting the YO
> instructions or something. For instance, It may be that the stacking
> feature of YO is only intended to tell me what the combined pattern will
> be, but I don't get that from the manual. (My manual is marked Version
> 7.5).
>
> What is the proper sequence of steps for optimizing a stack?
>
> 73,
>
> geo - n4ua
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