[TowerTalk] Stacking offset compensation

[Steve Harrison]

Ed, which way did you model it: fore-and-aft, or did you also model 
side-to-side??

It seems intuitive that if the offset is side-to-side (STS), then the 
main distortion would be the main lobe would decrease somewhat and be 
offset to one side, while the number of major sidelobes increased, as 
well as their amplitudes. The total amount of energy within a pattern 
must remain the same; so when you subtract energy from the main lobe, 
that energy gets added elsewhere into the sidelobes or even backlobes.

OTOH, fore-and-aft (FAA) offset would probably result in a shallower 
main lobe with rising major sidelobes on each side; i.e., the pattern 
gets "split" into a pair of mainlobes with a notch in between.

I would think that one can physically-simulate FAA offset by changing 
the phasing between a pair of aligned yagis. The amplitude would, of 
course, remain the same for both. Thus, it may well be possible to 
compensate for FAA offset by changing the phasing between the arrays 
(this presumes that there is very little interaction between the two 
yagis). It should be possible to calculate the necessary phasing line or 
L-C circuit parameters; but how to do so is quite beyond my abilities to 
comprehend 8-)

And if you have both FAA and STS offsetting, then you wind up with a 
complex offset starburst pattern that looks like a cartoonish drawing of 
an explosion  ===8-O

73,

Steve K0XP


On 12/28/2023 9:11 AM, sawyered at earthlink.net wrote:
> I actually did model this a number of years ago.  From memory:
>
>   
>
> What matters is the DE line up.  1 to 2 ft was not material.  A few tenths
> of a db.  However it started dropping off pretty quickly to as much as half
> the stacking gain for a 5 - 6 ft offset on 10M.
>
>   
>
> While its not perfect, you can compensate for the material part of the
> offset by shortening or lengthening one of the feed lines by the difference
> (figuring VF into the equation).  I would only bother if more than 2 ft on
> 10M or 3 ft on 15 or 20M.
>
>   
>
> Theoretical stacking gain is 2 - 2.75dB.  So knocking 1 db off of that
> (which is not hard to do) is a pretty big hit to the possibilities.
>
>   
>
> Ed  N1UR
>
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