HFTA kinda sorta calculates stacking properly. It seems to assume you get
the optimum 2.7db stacking gain whether the spacing is optimum or not. And
it draws the HFTA ray from the center point between the 2. So it would
calculate a 2 high stack of 20M yagis having an added 2.7db of gain even if
they are stacked only 20 ft apart and will draw the enhanced ray from the
midpoint between the 2 yagis.
TowerTalk mailing list