[Antennas] Tower location question ...

2002年8月25日 19:43:57 -0700

I'd really appreciate some advice here. I've got a 55' US Tower crank-up
tilt-over mast that I'm having trouble deciding where to install. The
trouble is that the foundation for this antenna tower is a very large chunk
of concrete, once you pour it, you aren't going to want to move it!
I plan to build a modest two or three element quad beam (10m, 15m, 20m) to
mount on top. My property is about 1000' above the surrounding terrain on a
ridge line. My home is very near the top, maybe ten feet of elevation below
the actual crest.
I had picked out a site for the tower that was fifty or sixty feet from any
structure and a reasonable distance from the basement shack wall to
facilitate the feedline routing. Directly north of that location is a thirty
five foot tall steel pole barn workshop, and directly north east of the
proposed tower location is our home which is also about thirty five feet
tall built mostly of wood with a shake shingle roof today but we plan on
replacing that with a steel roof eventually.
Now I'm having some second thoughts about that location.
For one thing, getting the tower sixty feet away from the two structures
puts it down hill about three to five feet. Alternatively I'm considering a
location north of the original proposed location that would be as close as
possible to the metal building, just allowing some margin beyond the turning
radius of the antenna when the tower is in it's twenty one foot tall
"lowered" position. I know that in general you would like to avoid near
field obstructions, but the question is, if you gain elevation, is it
possibly better to get closer to the building, enabling the radiated field
to get over the top of the building better? Or does putting the steel
building in the near field cause more loss of signal from interference with
the field? There is also a tall fir tree that would be closer to the near
field of the antenna in that location, located to the north east, just
around the east side of the metal building. Again not so close as to
interfere with the antenna turning radius, but just outside of that turn
radius. The tree is probably forty feet tall today and of course will grow.
In simple terms, to restate the question. If you've got something like a
metal building (or a tall tree) that is going to be near an HF antenna,
especially if the only location you can install the tower is slightly
downhill from the obstruction, are you better off getting farther away from
the obstruction while sacrificing some height, or is it better to get up
close to the obstruction to try to get a better shot over the top of it?
Make sense? I'd like any and all opinions, but tell me what it's based on,
hunch, experience, theory, etc.
Please copy answers to [email protected] so I don't miss them.
Thanks very much for taking the time to consider this.
73!
- Tom Scott
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27005 SW Neill Rd
Newberg, Oregon 97132
503-614-1223 - Work
503-330-6867 - Cell
503-538-5839 - Home
KD7DMH
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