[TowerTalk] Re: Was "antenna decisions"-- on a hill side!! With vinesand trees, too!

[w8ji.tom]

Hi All,

> I think it depends on the slope of the hill. I was told by several
people,
> including Jim Miller of Comtek (the 4-square expert and provider of the
only
> commercial phasing boxes), that it is important for the element
feedpoints
> to be at the same height. If you can manage that, I don't think the shape
of
> the terrain in the near field will have all that much effect, unless
you're
> on a *really* steep hill, have mountains right in your face on one or
more
> sides, or live in a box canyon. My comments, however, apply to
installations
> with an adequate number of ground-mounted radials (60+) per element. I
have
> no idea how terrain would affect an elevated radial system (e.g., radials
> sloping steeply uphill, etc.)

The slope of the hill matters generally very little if the antennas are not
shadowed from each other by obstructions, or unless you look into a "wall"
in a desired direction. Of course a 45 degree slope would be a problem, but
not a ten or twenty degree slope. I use a "real" ground system, since
elevated radials have been inferior in several cases I've seen and measured
(usually about 5 dB down from a good conventional system). 
 
Almost anything will work, depending on how complex you want to make the
phasing system. I phased a 40 meter dipole against a 135 ft shunt fed tower
on 160, and got good gain and F/B ratio. I had a 135 ft tower with 120
radials, and a dipole up 100 feet between two trees with the feedline
dropping vertically about 100 feet from the tower. I installed a good
radial system under the dipole and tied the feedline together and fed it as
a "T" antenna for 160. 

I built a phasing unit that could control phase and current ratios, and
simply adjusted it for maximum F/B ratio. I could easily get 30 dB F/B, and
about 4 dB of gain over the vertical tower alone! If I had no tower, I'd
have just installed two 40 meter dipoles (ladder line feed) and phased them
on 160, 80 (as T antennas) and 40 and up (as dipoles). That wouldn't be a
bad setup, multiple bands with directivity from two dipoles held up by
trees! 

My 160 meter four square has about  6 dB gain, and competes well against a
three element wire yagi on 160 meters at 250 feet. VK's and ZL's report it
is basically a toss up which antenna is better, with the verticals almost
always winning when conditions are poor and the yagi generally better under
exceptional propagation during grayline peaks.

73 Tom

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