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Re: Satellite Antenna Polarization Data



----- Original Message -----
From: <k5oe@aol.com>
To: <amsat-bb@amsat.org>
Sent: Thursday, March 16, 2006 9:29 AM
Subject: Re: [amsat-bb] Satellite Antenna Polarization Data

> Many of the sats have a predetermined polarization (at the satellite
antenna), but that does not guarantee that polarization will be constant at
the ground station.  From 4 years of working thousands of contacts on
various LEOs, I can absolutely state the ground station "view" of
polarization is practically random.  This is due to many factors, including
spin of the spacecraft, angle to the groundstation, approach versus retreat
of the spacecraft in relation to the groundstation, and Faraday rotation.  A
typical LEO satellite like AO-27 will change it's "apparent" polarization
several times during a pass.  This is why having switchable polarization on
circularly polarized antennas is popular.  I don't want to start the
argument over linear versus circular polarization, but I will state several
lessons learned:
> - the "correct" circular polarization is always best, but that means being
able to switch
> - linear is simpler and easier, but requires significantly more gain to
hear as well
> - a low gain antenna at the wrong polarization will be deaf to LEOs, thus
the common "fading" effect
>
> In short, selecting a RHCP antenna for a specific LEO satellite will not
be an optimum solution all the time, only some of the time.  If you want to
hear well all the time, either go for switchable CP or high-gain linear
antennas.  One of the reasons modest hand-held antennas work so well for
LEOs is because your wrist is connected to your ears via your brain... and
you automatically adjust for best polarization.
>
> 73,
> Jerry, M0MOE

Hi Jerry,

Happy to hear from you since AO40

You are right.

The best article that I have seen about the above matter is "The Advantages
of Circular  Polarization for Amateur Satellite Ground Stations" by John J.
Nagle ,K4KJ with 8 pages ,17 drawings and 8 photograph published in the
1975 ARRL TECHNICAL SYMPOSIUM September 12, 1975 Sheraton
Conference Center Reston Virginia.

Best 73" de

i8CVS Domenico
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