<<
I don't think any reliable information documented anywhere could ever answer
your questions with hard data. Information on effects of trees on low bands
has been impossible to find.
>>
In the late '60s / early '70s, I had a tree-supported vertical for
75 m when I lived next to Menotomy Rocks Park in Arlington, MA.
The top insulator of the vertical wire was at about 80 ft. and the
base feedpoint at about 17 ft. Four to six elevated quarter-wave
radials were used; the far ends of these varied in height from
12 to 15 ft. The antenna was surrounded by fairly dense woods
of pines and oaks in the 80 to 100 ft. height range. I did
notice a bit less efficiency when the oaks had leaves on them
in summer, but overall the antenna worked well.
The location was on the eastern side of a hill about 220 ft. above
sea level and about 7 miles from downtown Boston and the seashore,
so it was a good site for hitting Europe, Africa, and the Middle
East.
Comparison tests versus a dipole at 90 ft. gave about equal
results to the UK at 3000 miles, somewhat better (about 3-6 dB)
for the vertical into Germany, and considerably better results
for the vertical beyond 4000 miles to the Slavic countries and
to the eastern end of the Mediterranean. Time of day sometimes
influenced which antenna did better, but those were the overall
results. The vertical was always better for receiving DX
stations since it reduced the ratio of close-in stateside QRM
(NY, NJ, PA, etc.) to desired DX better than the dipole. This
was helpful in pile-ups even in cases where the dipole may
have been better for transmitting, such as into the Caribbean.
I'd think that on 160 m vegetation would be less likely to
absorb signal than on 75 m but I don't pretend to be an
expert on it. I think if the trees are heavily packed with
wet snow, that would be your lossiest situation.
Mark Connelly, WA1ION - Billerica, MA, USA
RF circuits page = "http://www.qsl.net/wa1ion/index.html";
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