[TowerTalk] Tree attenuation

[Jim Lux]

At 10:28 AM 11/7/2005, K7LXC at aol.com wrote:
>Howdy, TowerTalkians --
>
>     Here's an interesting PowerPoint presentation called Effects of Trees on
>Slant Propagation Paths that looks at signal attenuation thru trees. It
>generally covers VHF and above but you can probably make some inferences 
>for HF. If
>someone can summarize it for us non-engineering types, I'd appreciate it. 
>Tnx.
>(If anyone has info related to HF, please post it. Tnx.)
>
>http://www.its.bldrdoc.gov/isart/art99/slides99/vog/vog_s.pdf


There's a more complete version of this at Utexas..
http://www.utexas.edu/research/mopro/
In particular, you might be interested in Chapter 2 and 3

The summary is that at low angles, the attenuation is a function of 
distance... a certain number of dB/meter, depending on the kind and density 
of trees.

At high angles, the attenuation is a fixed number.. some number of dB.

Polarization is important.. attenuation is higher for V pol


As far as HF goes, it gets quite a bit more complicated(!), for two reasons:

1) The forest scale (height of trees, etc.) is on the same order as the 
wavelength  (at VHF, trees are MUCH bigger than a wavelength, and leaves 
are MUCH smaller).

2) Most practical applications of a model have the antenna in the forest, 
where the forest is in the near field of the antenna.



>Cheers,
>Steve      K7LXC
>TOWER TECH
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