Gentlemen:
I wanted to weigh-in on the discussion of the impact of tree losses on
transmitting antenna performance. Of course I have no quantitative
data, but experience is suggestive of potentially significant losses.
I used to live in Grayson County, Virginia, on a completely wooded
hilltop. By completely wooded, I mean a dense mixed forest, with a
fair percentage of pitch pine in the immediate area of my lowband
vertical. I built a version of the Battle Creek Special that was 40'
high and had a fairly sparse radial field, with (8) 135' radials, (16)
66' radials, and (16) 35' radials -- all insulated copper. The
antenna was on a small knoll, which dropped off gently in all
directions. The forest were quite dense and low angle radiation had
to travel through hundreds of feet of forest to finally clear the
ground clutter. I used that antenna for several years and became well
acquainted with its characteristics. In good conditions and with
50-watts, I could work out 6000 miles or so on 160-meters. I remember
it was a struggle to work Eu and I was quite unable to work JA or VK
in two seasons. Eventually, I moved to a small farm at the bottom of
a valley in Pulaski County, VA, and transplanted the Battle Creek
Special, radial field and all. I would have called it a worse RF site
than the Grayson County site, but the results indicate not. There are
very few trees anywhere near the antenna and the takeoff angle from
due West and through North and to the East is unobstructed, with the
hill falling away in those general directions. The southern half is
less favorable and actually slopes uphill. The soil conductivity in
the pasture may be a bit better, but the relative lack of trees is a
big difference. At the old location, a 500' circle contained
hundreds of trees, vs. the new QTH which has a dozen or so in the same
radius. The difference in the performance of the antenna was
noticeable in that I could now work EU routinely and also worked JA
and VK on Topband for the first time--with the same 50-watts output.
Of course, there were more variables than tree density in this story
and no way of knowing for sure how many others were present. There had
to be some some absorption of the signal due to gently heating tree
sap and certainly losses due to gently heating earth and earth worms.
The two locations were about 70-miles apart and quite different--one
mountainous and one agricultural, so the take-off angles were likely a
bit different too. It's hard to quantify all that, but operationally
there is no question which installation gave the better results on
Topband, by a fair margin.
73,
Steve, AB4I
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Topband Reflector
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