[HATS] 2.4 GHz and trees, FYI

[Ron L. Sparks]

The following excerpt is interesting (heck the whole paper is very
good - reccomended):

"Attenuation from Trees and Forests
Trees can be a significant source of path loss, and there are a number
of variables involved, such as the specific type of tree, whether it
is wet or dry, and in the case of deciduous trees, whether the leaves
are present or not. Isolated trees are not usually a major problem,
but a dense forest is another story. The attenuation depends on the
distance the signal must penetrate through the forest, and it
increases with frequency. According to a CCIR report [10], the
attenuation is of the order of 0.05 dB/m at 200 MHz, 0.1 dB/m at 500
MHz, 0.2 dB/m at 1 GHz, 0.3 dB/m at 2 GHz and 0.4 dB/m at 3 GHz. At
lower frequencies, the attenuation is somewhat lower for horizontal
polarization than for vertical, but the difference disappears above
about 1 GHz. This adds up to a lot of excess path loss if your signal
must penetrate several hundred meters of forest! Fortunately, there is
also significant propagation by diffraction over the treetops,
especially if you can get your antennas up near treetop level or keep
them a good distance from the edge of the forest, so all is not lost
if you live near a forest. "

>From http://www.tapr.org/tapr/html/ve3jf.dcc97/ve3jf.dcc97.html

Also a good paper "Attenuation from Trees : Static Case" at
http://www.utexas.edu/research/mopro/papercopy/chapter02.pdf

It also agrees with the 0.3 dB/M number at 2 GHz.

So, if you have to look through one tree that is about 33 ft (10 M)
thick at the point you must "see through" you will lose about half
your signal (3 dB).  Which can possibly be compensated for.  On the
other hand, if you have a half a mile of trees (800 M), I would bet
you will have a real hard time making up for the 240 dB path loss.

Good Luck,

Ron, AG5RS

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