> My colleagues want to be able to readily repurpose a mounted
> directional antenna, so that it would be easy to point it at site A
> then quickly rotate it to point at sites B, C, or D. We are
> thinking a computer-controlled telescope mount would work, or a
> pan-and-tilt unit used for cameras and lights.
>
I have built something along the lines of what you describe above, but for
survey and site finding. However, I wanted continue to enjoy the
telescope and purchased extra lens and camera mount covers for the
ETX and attached plastic mounting brackets to the covers that can be
easily removed when not being used for wireless purposes.
If you are a linux person, you may want to look at the xephem software
package for routines to drive an ETX telescope mount via the
serial/parallel port. Xephem comes with source, so you can extract the
tracking routines for your purposes. It is fun pull down keplerian
elements and track satellites with it though. I've toyed with attaching a
small parabolic dish to the end as well for sweeping the skies with it
attached to a spectrum analyzer. It's pretty neat to watch it track
across the sky. Some of the amateur radio OSCAR satellites operate with a
2ghz downlink frequency.
> The Meade telescope units look pretty sturdy, but the question is
> whether you can actually remove the telescope. The pan-and-tilt
> units from Directed Perception have a rating of only 6lbs, which is
> enough for the antenna but I worry about wind loading.
>
For a permanent solution, you should definatley use one of the directed
perception az/el positioners. There are procedures on the net to totally
dismantle an ETX telescope, but the base is bulky, and it is a shame to
ruin a telescope for a wireless project. You would also have the problem
of windloading and other environmental effects to worry about with either
mount.
At a wireless event on the East Coast here, a few members of BAWIA
(Boston Area Wireless Internet Association) and I were discussing such a
system. We discussed various possiblities including using electrically
controlled coax switches and a few patch antennas, electronically
steerable patch antennas and the one we are presently talking about.
Although the most mechanical, the cheapest and least difficult to do is
the steerable antenna via a mechanism like the Directed Perception. With
a properly designed radome, similar to a saucer like design, giving you
~360 azimuth coverage, a +/- of 20deg elevation tilt, you can point at
almost any terrestrial link. The only execption would be one on a
significantly higher elevation than your own. Of course, you can play
with the radome design to accomodate you potential links.. say you live
in a hilly or mountainous area, then you may want to increase your
elevation tilt parameters to +/-45 or 50 degrees to be able to point up
at higher locations.
The radeom can be made from two large plastic trashcan lids or some other
plastic storage containers. They come in many shapes and sizes. Those in
colder climates will need to worry about ice load on the structure. At
some point I will complete and document an outdoor mount and document
my progress to date.
Anyone that is involved in a free network will understand that serving
nodes can come and go as the clouds. This can be very disruptive to the
network, and having a few of the main distribution centers be able to
dynamically reconfigure when one of the peers disappear will save yet
another waltz with death balancing up on the roof or tower re-orienting
the yagi, parabolic, or patch antenna.
As networks become more dense, there may be a variety of AP's to select
from, and one may wish to be able to dynamically steer the antenna toward
the best AP or periodically sweep for less used ones.
Brian
bmh at xa . net
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