[amsat-bb] Antenna Polarization Question

[Burns Fisher]

Aha!  Most reasonable answer I’ve heard!  Thanks!

On Sun, Mar 18, 2018 at 10:21 PM Greg D <ko6th.greg at gmail.com> wrote:

> 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 at 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 at gmail.com>
> >>  To: Eduardo PY2RN <py2rn at arrl.net>
> >> Cc: Brian <cqkg8co at yahoo.com>; "amsat-bb at amsat.org" <amsat-bb at 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 at 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 at amsat.org>
> >>  To: "amsat-bb at amsat.org" <amsat-bb at 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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> >>
> >>
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> > _______________________________________________
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> > to all interested persons worldwide without requiring membership.
> Opinions expressed
> > are solely those of the author, and do not reflect the official views of
> AMSAT-NA.
> > Not an AMSAT-NA member? Join now to support the amateur satellite
> program!
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>