[TowerTalk] HTFA and Reality

[Jim Lux]

At 02:02 AM 1/23/2007, Kjeld Holm wrote:
>Gentlemen:
>
>I am using HFTA in planning for an array for 10 to 20 m. Due to zone
>restrictions I am modelling a lot of solutions - normal and crazy ones among
>each other. As I may end up being restricted to a top point of 26 feet I
>modelled a 4 stack of 2 elements yagis at 17/20/23/26 feet. According to
>HTFA this should work fine on all three bands (less performance on 20 m of
>course). But I do not believe in such a close spacing in the real world. Any
>comments would be appreciated.

I don't think HFTA models the interaction between antennas, rather, 
it assumes that they are idealized point source radiators with a 
specified elevation pattern and gain, and then just sums the 
contributions.  A note to Dean Straw, N6BV, would probably find out 
the real deal.

So, what you'd need to do is run a model in NEC or equivalent of your 
stack of antennas to find out the "free space" gain and effective 
phase center(s).  Then, plug that into HFTA to get the terrain effects.

Jim, W6RMK