[TowerTalk] Tree attenuation

[Jim Lux]

At 04:28 PM 11/7/2005, Tom Rauch wrote:

>Hi Fred,
>
>Respectfully, there are far too many variables involved to
>say how much or even if the trees bothered anything. The
>only way to tell how much difference the trees actually make
>would be to use exactly the same location and installation
>with the tress and then without the trees and measure the FS
>change over a stable path.

Which is what the folks did for the research.  At HF, especially on low 
bands (40 and below), it seems you're probably looking at a maximum few dB 
difference because of the trees, and as you note, there's a whole lot of 
other potentially confounding factors.


>Everything I have observed is trees make very little
>difference at lower HF. My last house had vertical antennas
>nestled in trees, and everything appeared to work as well as
>any other stations in pileups. I can't imagine a horizontal
>antenna being worse.

Actually, the data seems to show that the horizontal antennas do slightly 
better in terms of the power actually radiated out.  The ionosphere is 
going to scramble everything anyway as far as polarization.

Of some practical interest, and I'll try to find out some more, is the 
observation by Tamir (based on the research from Jansky and Bailey(1965), 
Egli(1957), and Head(1960)) that the forest tends to reduce the effect of 
terrain.

This would make effective utilization of programs like HFTA somewhat 
tricky, since HFTA uses geometric theory of diffraction and inherently 
assumes a "bald earth"


>73 Tom