[amsat-bb] Antenna Polarization Question

Mon Mar 19 18:33:29 UTC 2018

I'd really like to understand this better, but it is still not making sense
to me.  I believe that if you are transmitting with a CP antenna, the E and
M waves actually go through an entire circle in one carrier cycle and a CP
antenna is able to "follow" that.  Surely a satellite is not spinning at
anywhere close to 145 or 450 million revs per second, so I don't get
"spinning satellite" as an explanation for why an LHP or RHP antenna might
work better at different times.

What I do get is that a CP antenna can receive linearly polarized waves at
any angle equally.  But this should be true whether the antenna is LHP or
RHP, and I would not think which direction should matter if the signal is
linear in the first place, even if the signal is spinning slowly.

That all said, I have definitely heard people say that they can get better
reception by changing from LHP to RHP.  I'm not saying this is not true.
Just that I don't understand it.

73,

Burns WB1FJ

On Mon, Mar 19, 2018 at 1:57 PM, Jean Marc Momple <
jean.marc.momple at gmail.com> wrote:

> Guys,
>
> Long debate for not much. I have followed this stream and believe that I
> need to intervene.
>
> It is very simple, most HAM birds does spin (sometimes a lot) and there is
> no way one can anticipate as different from one bird to others. It is just
> operator skills (on the spot) to determine/switch from LHCP or RCCP based
> on what  is the best received signal strength. It works both on the Uplink
> and Downlink. There is no miracle formulae and it is a just operator skills
> as mentioned before.
>
> For commercial birds it is totally different game and should not be
> compared with our humble Ham birds, they have much more means to do things
> that we cannot afford to do, except if all HAM worldwide donate to AMSAT,
> say $10 we then may be able to match some of the features commercially
> available.
>
> Just a suggestion and food for thought.
>
>
> 73
>
>
> Jean Marc (3B8DU)
>
>
> > On Mar 19, 2018, at 8:54 PM, Franklin Antonio <antonio at qti.qualcomm.com>
> wrote:
> >
> > 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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> Opinions
> >> expressed
> >> are solely those of the author, and do not reflect the official views of
> >> AMSAT-NA.
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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
> >> 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
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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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> 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 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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>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> 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!
> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb
>