On 4/9/2014 10:04 AM, Brian Alsop wrote:
I'm not sure one would ever notice the tree effects on HF. There are
lots of other things (e.g., no balun at the feedpoint, feedline
routing and objects in the near field, ground terrain variations )
that would probably be larger effects.
I have Satellite, and off the air TV. Several trees grew into the
"line-of-sight" between the antenna and UHF station. It's not true that
with digital you either receive, or don't receive the signal. The range
between signal and no signal is much narrower than it was for VHF
analog, but there is a range. We noticed that on occasion the signal
would "pixelate" and pause. As time went on this happened more often. I
put the UHF antennas at roughly 90 feet on the 45G with a clear shot.
Surprisingly, even with the longest antennas I could find, they do well
up to 20 or 30 degrees off axis with a range in excess of 100 miles. So
at UHF, (including 440) the regular, leafed trees do have a strong
attenuation of the signal. They seem to have little, if any effect on
160 through 40. I don't know about 20 through 10.
NOTE. With one antenna pointed between Detroit and Lansing, I could
receive both quite well, but had to move the antenna to get the Grand
Rapids area. With an antenna pointed to the NW I could receive both
Cadillac and Traverse City (bout 70 and over 110 miles)and within 10
degrees of each other.
Any vegetation seems to block the satellite signal. Which is much
higher in frequency. The same goes for wireless Internet.
It's surprising how far away an antenna for 75 and 40 can be from others
and still show effects even in SWR and resonant point although they were
apparently not sensitive to trees.
A 40 meter vertical antenna (AV640)displayed shifts in the resonant
frequency when slopers were erected several wavelengths distant. (50 to
100 KHz)
The base of the AV640 is about 25 feet above ground.and 50-75 feet from
the trees.
73
Roger (K8RI)
I had an commercial BC TV engineer relate to me a story of the
importance of attenuation in "trees" for HDTV (UHF). One station near
the NC coast (beaming inland) made an argument that the long leaf pine
needles were the right size to selectively attenuate their signal.
They managed to get a somewhat higher permitted power. It would have
been interesting to actually have a measurement of the effect.......
73 de Brian/K3KO
On 4/9/2014 13:52, john@kk9a.com wrote:
I have had great results with dipoles hung in trees.
John KK9A
To: towertalk@contesting.com
Subject: [TowerTalk] Fwd: Fwd: Hustler 6-BTV installation
From: Hans Hammarquist <hanslg@aol.com>
Date: Wed, 9 Apr 2014 00:02:05 -0400 (EDT)
Have the same experience hanging various verticals from trees. I
guess if you
have a perfect, non-conducting tree it will work. Unfortunately trees
are
somewhat conducting, enough to mess up the radiation.
It will work better if you don't use a tree but a non-conducting
support such
as a large plastic pipe. A thicker, self-supporting conductor such as
a tube
would also work.
Maybe you get what you pay for.
Best 73 de,
Hans - N2JFS
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