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Re: UO-22 azimuth-only system



John Pfeifer <john@johnpfeifer.com> wrote:

>Now that I'm taking a short break from all the fun I've been having on 
>AO-40, I'm starting to think about that LEO antenna system I've been 
>meaning to put up.

>I'm using UO-22 as a design point because I'd like to try the PACSATs.  My 
>research on the net indicates most people on UO-22 are using gain antennas 
>and az-el rotors, especially on receive.

Yep. This is the usual approach, and while it can
be costly to set up, it works well.

>Since I'm using an armstrong system for AO-40, I don't really want to spend 
>the money on an az-el rotor system. But, I am considering putting up an 
>azimuth-only system using APRStk.

>Has anyone out there had experience using a modest cross yagi for UO-22 
>receive?  I'm thinking about 5 or 6 elements, switchable RHCP/LHCP with a 
>good preamp, something on the order of 60 degrees/3db beamwidth with a gain 
>of 9-10 dBi.

Steering antennas during LEO passes can be very exciting.

People have done research on this - trying to match the
gain of an antenna with the position and range of the
satellite. Get it right and you don't need to steer the
antenna at all, because the main lobe of the antenna's
pattern coincides with the most likely location of
the satellite.

I have a thesis in my files on the subject (I think
I still have it...), and proposed this as a research
project at school. I envisioned a phased vertical
array with the main lobe at a suitable elevation.
The Powers That Be couldn't see beyond the end of
their dic^H^H^Hnoses, so that's as far as it got. With
the demise of TO-31 (I could hear it on a handheld
scanner with a rubber duck antenna on high-elevation
passes) I haven't been able to muster the enthusiasm
to pursue it myself.

>If that leaves me too much of a hole directly overhead, I could supplant it 
>with a Moxon turnstile array (switchable RHCP/LHCP, ~5.5 dBi gain).

Before you do, please run some simulations to see
just how much you lose in the hole. The satellite
just doesn't spend much time there. Not enough to
worry about, unless you want 100% downlink effi-
ciency from AOS to LOS - in which case this is
entirely the wrong approach anyway.

>For transmit, I'm thinking 3 or 4 el. yagi, vertically polarized, aimed 
>about 30 degrees up.

The uplink transmitters are sensitive, and you can
always increase your transmitter power. This can
be an effective compromise.

Laura Halliday VE7LDH     "Que les nuages soient notre
Grid: CN89lg                    pied a terre..."
ICBM: 49 16.57 N 123 0.24 W        - Hospital/Shafte

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