[amsat-bb] Re: Antennas
bruninga at usna.edu
Thu Dec 14 11:40:49 PST 2006
> ... but what would be the best antenna to work LEO birds
> like AO-51 and some of the cubesats ... without an
> AZ/EL rotor...
That is the right approach. A simple $75 TV rotator will do 98%
of what the $600 AZ/EL mounts can do for LEO's. AND you don't
need the LONG yagi's either, since they are only needed for high
orbiting satelits of which there are none right now.
Remember these numbers. 66% of all pass times are below 20
degrees elevation. 85% are below about 45 degrees and 98% are
below 60 degrees or something like that. So just put your arrow
on a TV rotator and tilt it up about 15 degrees. Done.
If you can't see down to 15 degrees above the horizon due to
trees, then you are already losing out on 66% of all pass times,
but then you may as well tilt up to about 30 deg and nail the
remaining 33% with a little more gain. You don't need any gain
abouve 30 deg, because the satellite is already 6 to 10 dB
closer to you than it was on the horizon anyway. That is why a
fixed antenna at 15 degrees works very well. See it all on
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