Re: [amsat-bb] Antenna Polarization Question

19 Mar 2018

      Hi Burns,
I've experienced that too, and from a little research I think it has
more to do with mechanics, and less physics.  The thought is that no CP
antenna is perfectly circular, and so has a linear component to the
pattern.  That linear component's alignment, or mis-alignment, with the
satellite's antenna causes some fading.  Flipping the handedness also
changes the angle of that linear part, so it can help (or hurt) the
reception.
At least, that's the theory.  There may also be reflections from
buildings and the planet that will introduce a linear component to the
signal, and perhaps some atmospheric effects as well.
Greg  KO6TH
Burns Fisher wrote:
...
Indeed, CP makes sense with a linear tx when you can't tell what the
orientation would be.  You give up a few dB to avoid deep fades.  But I
just can't figure out why you need to switch from RHP to LHP in such
cases.  I've heard a number of people say that it sometimes matters, but I
don't understand the physics!
73,
Burns WB1FJ
On Sun, Mar 18, 2018 at 6:06 PM, Eduardo PY2RN py2rn@arrl.net wrote:
...
Jordan,  most of the amateur radio LEOs SATs today have a linear polarized
antenna attached, it is not possible to know which position it is in the
time of the pass: H, V, moving, spinning... being completely random to the
ground station which polarization the signal will be, for this reason I
believe CP is more efficient but with RH/LH switching capability.
73
Ed
PY2RN
      From: Jordan Trewitt jmtrewitt@gmail.com
 To: Eduardo PY2RN py2rn@arrl.net
Cc: Brian cqkg8co@yahoo.com; "amsat-bb@amsat.org" amsat-bb@amsat.org
 Sent: Sunday, March 18, 2018 6:44 PM
 Subject: Re: [amsat-bb] Antenna Polarization Question
Maybe I'm not understanding it, but why does one need to switch between
both, unless a particular satellite has LHCP or RHCP?JordanKF5COQ
On Sun, Mar 18, 2018, 16:34 Eduardo PY2RN py2rn@arrl.net wrote:
Hi Brian,
Both. You are going to need to switch between RHCP and LHCP often during a
sat pass. The same happens if using linear polarization (V/H) but in this
case the switch between V and H will happen much more often than in CP.
73
Ed
PY2RN
  From: Brian via AMSAT-BB <amsat-bb@amsat.org>

To: "amsat-bb@amsat.org" amsat-bb@amsat.org
 Sent: Sunday, March 18, 2018 6:21 PM
 Subject: [amsat-bb] Antenna Polarization Question
Should I be using LHCP or RHCP when setting up the 2 meter and 440 yagi's
to work the LEO's.
Thank you
Brian, KG8CO

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Re: [amsat-bb] Antenna Polarization Question

Greg D