[amsat-bb] Antenna Polarization Question

[Greg D]

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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> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. Opinions expressed
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> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb