[Antennaware] Using YO to analyze stacked Yagis
Pete Smith N4ZR
n4zr at contesting.com
Sun Feb 26 12:35:52 PST 2012
Just a couple of comments. A stack of 2-element beams can be effective
if you get the spacing right. I have a stack of C-3s, and did a lot of
modeling with EZNEC back in the day. Wound up with the best compromise
(for these tribanders) at 28 feet, somewhat closer than generally used
for TH-7s and the like.
This stack is quite good. I've found, however, that top alone is rarely
better, because the take-off angle at maximum gain is the same as for
the stack, but the lobe is narrower. Bottom only, by contrast, produces
a usefully-higher first lobe, and quite often produces higher run rates
late in an opening. The stack would have been more flexible if I could
have stacked a third one between the bottom one and ground, but my tower
wouldn't take it.
73, Pete N4ZR
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On 2/26/2012 3:21 PM, Guy Olinger K2AV wrote:
> 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 at 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
>> What is the proper sequence of steps for optimizing a stack?
>> geo - n4ua
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