[TowerTalk] Two 15m yagi stacking

[Jim Lux]

At 05:16 PM 2/23/2007, BA7NQ Terry wrote:
>I am preparing make my first yagi stacking for contest station and
>researching some document from internet. The tower will have 30 meters high,
>and I have two 5 element yagi.
>
>My question is:
>
>1) The separation distance between two yagi? Some documents said is 3/4
>wavelength, or 5/8 wavlength, or 0.62 wavelenght. How to consider this space
>vs stacking performance?
>
>2) My idea is, the bottom yagi fix to EU, and the top yagi is rotatable,
>when the top yagi beaming to EU, then switch the two yagi to "BOTH", is this
>right?
>
>3) About the YAGI, I found many station use 4 element or 5 element yagi for
>stacking,  is high-elements good for stacking or just 4 or 5 elements
>better?


The best way to answer these questions is to get a copy of HFTA, 
which comes with the ARRL Antenna book. It lets you model the pattern 
of stacked antennas, varying spacing, etc., and factoring in your 
terrain, as well.  You just select the kind of antenna (e.g. 5 
element beam), and the heights and frequencies, and it plots out 
patterns (using generic patterns based on nominal performing antennas).