[TowerTalk] Tree attenuation
jimlux at earthlink.net
Mon Nov 7 17:12:53 EST 2005
At 01:24 PM 11/7/2005, you wrote:
>On Mon, 07 Nov 2005 12:15:59 -0800, Jim Lux wrote:
> >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.
>I skimmed both the Power Point and the longer document. The analysis that
>into the Power Point make it considerably more valuable in guestimating what
>might happen at VHF and low UHF, but neither gives much insight into HF.
>The obvious question is, is anyone aware of anything equally good for the HF
>spectrum? My future antenna supports are likely to be redwoods, 25-30 meters
The short answer is no.
There's not much research interest in HF frequencies at least as far as
propagation through forests. People who have serious money to spend on HF
antenna installations where loss would be important either site them were
there is no forest or cut down the trees.
There is some propagation data from the 60s and 70s, collected for jungle
type environments. There's also some recent low VHF data from Brazil, also
for a jungle.
There's no nice summary presentation all put together, unfortunately.
It might be worth calling or writing Vogel at U of T Austin.
>Jim Brown K9YC
Jim Lux, W6RMK
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