> On Sun, 8 Aug 1999 14:13:13 -0400, Tom Rauch wrote:
> > I'd wager there is NOT an abrupt change in
> > anything at the tree level at HF, since even 144 MHz signals are
> > barely affected.
> Can't speak for the HF side, but 144 sigs are very much attenuated with
> trees. There is a tremendous change in signal levels between winter and
> summer when the vegetation is on the limbs.
Attenuation and other effects vary with distance the wave travels
through the media. In a stand of trees 500 feet thick, we measured
almost three dB of extra attenuation on 144 MHz over the same
path distance in winter. At 2 GHz, attenuation was so great we
couldn't even measure the signal level from a 2500 watt ERP
system at the other end during summer. On 1370 KHz, we couldn't
tell any difference at all, summer or winter.
Comparing a signal that travels miles through trees on two meters
is pointless at HF, because most of the pattern is formed within a
several hundred feet.
73, Tom W8JI
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