[amsat-bb] Antenna Polarization Question

[Robert Bruninga]

Another way to understand it is that the if in any given direction the
combination of the emission from a cubesat with only one or two antenna
elements appears RHCP in one direction, it will appear LHCP in the
opposite direction to the same extent.

So during a pass or due to tumbling, you can see both

I think.
Bob, WB4aPR

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Greg D
Sent: Sunday, March 18, 2018 10:21 PM
To: Burns Fisher <burns at fisher.cc>; Eduardo PY2RN <py2rn at arrl.net>
Cc: amsat-bb at amsat.org
Subject: Re: [amsat-bb] Antenna Polarization Question

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.
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the official views of AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite
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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
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views of AMSAT-NA.
Not an AMSAT-NA member? Join now to support the amateur satellite program!
Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb