[TowerTalk] Optimum yagi stacking distance

[David Gilbert]

HFTA is a terrific program but it has a known error when analyzing 
stacked antennas. It gives you good guidance for deciding the heights of 
stacked antennas to optimize the pattern for your particular terrain, 
but it exaggerates the combined gain for close spacings. The following 
paragraph is taken directly from the Help file that accompanies HFTA.

"The internal Yagi model in HFTA is a simple mathematical model. It does 
not compute interactions between individual Yagis in a stack—HFTA 
assumes that each antenna is a “point source.” For antennas stacked more 
than about a half wavelength apart this is not a problem. For example, 
you should be cautious specifying spacings less than about 20 feet on 20 
meters (and proportionately scaled on other bands) because of 
mutual-coupling effects between real antennas."

Personally, I think 30 feet spacing is as low as I would go for 
tribanders, especially if I had the ability to select top/bottom/both.

73,
Dave AB7E




Gary Slagel wrote:
> More questions from a yagi stacking rookie!
>
> I've been using the HFTA software to try and get an
> idea of the optimum distance to stack a couple yagis
> for best performance.  I'm stacking 10/15/20
> tribanders for increased performance.  I was really
> surprised that on most bands the optimum performance
> seems to be with them separated by only about 10'...
> for instance 65' and 56'!  I expected it to be more
> like 20' to 30'!  
>
> I wonder how this jibes with folks with real
> experience?
>
> Thanks,
> Gary
>
>
> Gary Slagel/N0SXX
> Lakewood, CO
> http://marina.fortunecity.com/sanpedro/351
>
>
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