At 10:28 AM 11/7/2005, K7LXC@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
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>any questions and ask for Sherman, W2FLA.
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk@contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|