On Tue, 3 Nov 2009 10:45:48 -0500, Guy Olinger K2AV wrote:
>Some interesting anecdotal-level experiments that suggest that there is no
>great loss.
Since I live in a dense redwood forest, I've done my best to learn as much
as I can about this. While I agree with Guy as to the difficulty of
learning anything solid, I don't think it's quite as rosy as W8JI's
research suggests ON ALL BANDS.
My take, which is the combination of my experience and that of my neighbors
who think in solid engineering terms, is that losses due to trees:
1) Are greatest for vertically polarized antennas than for horizontal ones
2) Increase with frequency (although probably not linearly)
3) are no big deal for horizontal antennas at HF and 6M, start getting
significant at 2M, are a big deal at 440MHz, and are a wipeout at 900 MHz.
A colleague with considerable experience at UHF and above says, "at cell
phone frequencies, think -3dB per tree." I can tell you that no one's cell
phone works up here, and propagation to 440 repeaters is quite poor.
4) are probably not a big deal on 160M for vertical antennas on 160M, but
may be significant at 40M and above. I have, for example, tried a 40M
vertical over the same set of radials that I installed for 160M, and it was
a complete waste of time. It's in the middle of big clearing (roughly 75 ft
radius).
I have a vertical dipole for 40M hanging from a 170 ft redwood, with the
feedpoint at about 80 ft. It is a block of wood compared to my horizontal
dipoles at 120 ft. Part of that difference is predicted by the pattern of
the antenna over ground, but my experience with it suggests that there is
also some loss from the tree. I could be wrong, and one of the things on my
"to do list" is to set up a second version of this antenna that is not
close to a tree.
73,
Jim Brown K9YC
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160 meters is a serious band, it should be treated with respect. - TF4M
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