[amsat-bb] Antenna Polarization Question

[Franklin Antonio]

When you say a satellite "has" RHCP, we have to be careful that we're communicating clearly about what "has" means.  Every satellite "has" both, by virtue of he way antennas work.

I suspect that you mean that the satellite has an antenna which transmits RHCP in its main lobe.  It is important to realize that the signal from such an antenna is only RHCP in its main lobe.  The sidelobes are gonna be LHCP.  In between, you can get anything in between.  So if a satellite is oriented so that its antenna points right at you, and they designed it to be RHCP, then that's what you're gonna get, but if it is pointing off to the side, then you get something else. 

This means that there are situations in which you might get a stronger received signal if you switch to LHCP, or maybe even to linear.  In the commercial satellite biz, they design satellites so that their antennas point at the users.  Hams build cheaper satellites, which typically don't have sophisticated attitude control, so sometimes they point away from you.  Also, hams try to use the things even when conditions aren't the best.  If that's your aim, then most folks have found that polarization switching sometimes helps.

________________________________________
From: AMSAT-BB <amsat-bb-bounces at amsat.org> on behalf of Jordan Trewitt <jmtrewitt at gmail.com>
Sent: Sunday, March 18, 2018 2:43 PM
To: Eduardo PY2RN
Cc: amsat-bb at amsat.org
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?
Jordan
KF5COQ

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