[TowerTalk] [CQ-Contest] Stacking on separate towers, take off angles?

[Dan Maguire]

--- Stan Stockton wrote:
> Model this.... Put two mono- band antennas at same height on separate
> towers with the towers about 1.5 wavelengths apart and the antennas in
> phase. ... I think you will like what you see.

Not sure if Stan was addressing me or the original poster but it sounded like a fun exercise.  I modeled two Yagis, each at 1.5 WL above real/average ground, separated horizontally by 1.5 WL as though on two separate towers, with each antenna being rotated by amount "D" degrees.

Here's the EZNEC view, looking straight down from above, as "D" is incremented from 0 to 90 in 15 degree steps.
http://ac6la.com/adhoc/TwoTowerArray.gif

Because the resulting pattern is so convoluted with "D" at anything other than 0 it helps to run a 3D calculation for each test case and then see where the max gain is in terms of Az/El angles.  In this AutoEZ screen grab the 3D results are enclosed in red on the right.  Notice that at anything other than 0 deg of rotation the azimuth angle of the max gain point doesn't have much to do with the amount of Yagi rotation.
http://ac6la.com/adhoc/TwoTower3DCalcs.png

For most of the test cases the max gain is at 9 deg elevation, so here is what the azimuth pattern looks like at 9 deg elevation as "D" is varied from 0 to 90.  Outer ring has been frozen so you can see the difference in gain as well as the difference in pattern shape.  With most browsers you can use Esc to stop the animation and F5 to restart.
http://ac6la.com/adhoc/TwoTowerAzimat9el.gif

And here is the azimuth pattern at 31 deg elevation when both antennas are pointing at 90 deg azimuth.  This is the same as the last frame of the above animation except that the elevation angle is 31 deg instead of 9 deg.
http://ac6la.com/adhoc/TwoTowerat31el.gif

I'm not so sure about "liking what I see."  Maybe Stan had his tongue in his cheek when he said that.  :)

Dan, AC6LA
http://ac6la.com/