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Author Topic: HF Attenuation Through Trees  (Read 413 times)
KB1NLW
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Posts: 69




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« on: September 22, 2008, 02:14:11 PM »

Any one know where I can find some quantitative information on attenuation through trees?
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WI7B
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Posts: 53


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« Reply #1 on: September 23, 2008, 03:52:52 PM »


I guess my first question is "quantitative information" of on what quantity?

RF radiation...solar radiation, what?  If RF radiation, on what frequencies are you interested in having information.

For example, an experiment was performed in which a 30-foot maple tree was placed between a 2-foot parabolic antenna and a distant transmitting site operating at 20 and 44 GHz. The objective was to measure attenuation through foliage. Results indicate that attenuation is nearly the same at the two frequencies. A value of 4 dB/meter can be used as a rough guide for deciduous trees in full leaf. Measurements on single maple leaves and pine needle clusters plus a study of the literature tended to reinforce the conclusions of the tree experiment, and to show that evergreen trees can be expected to have similar attenuation values.

And of course, there is a reason that 800 MHz RF towers are NOT placed in pine forests.  Can you 'guess' why?  Typical pine needles are 1/4 wavelength resonators!

In contrast, it is well known that at HF through VHF, the propagation between two distant points within a forest experiences significantly LESS attenuation than that predicted by direct path field calculation. That is, the predicted attenuation of the direct wave far exceeds the attenuation values obtained from experimental results.

73,

---* Ken


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