This spring I began removing 10 mature loblolly pines, around 85-90 feet
tall, that surrounded my Rohn 25 driven element in a K3LR 160-meter
parasitic array. When the tower was installed in 1998, the trees were around
30 feet tall and were no problem to maintain, but in recent years the
trimming became more difficult as they grew and limbs became entangled with
some of the guys. Several of the pines were as close as about 12-15 feet
from the tower.
Today my son Adam, N3TTT, and I took down the last two pines. Before we did,
I took measurements at the feedpoint of the series-fed tower with my Rig
Expert AA-230 Zoom antenna analyzer.
What we found was there was no significant change in SWR, resonant
frequency, impedance, etc., when the trees were there and when they were
removed.
This array, described in ON4UN's Low Band DXing book, has 120 quarter-wave
radials under each of five elements, slightly buried and bonded to a
midpoint buss wire between each element. The 119-foot tower has a 6-meter
5-element yagi for top loading and is resonant around 1470 kHz. I use an
L-circuit matching network at the feedpoint. There has not been any need to
change the matching network since the tree removal began.
Since there has been occasional discussion of the effect of trees on
antennas, I'm sharing this with the group.
73/Jon
Jon P. Zaimes, AA1K
Tower climber for hire
http://www.aa1k.us/
Cell: 302-632-2353
Reviews of AA1K tower work on eham website:
http://www.eham.net/reviews/detail/12922
Hug your favorite tower every day, and always stay connected to it.
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