[amsat-bb] Does SO-50 Tumble? Was: "Polarization"

Thu Jun 2 23:40:01 UTC 2016

PCSAT spins at about 0.6 RPM and PSAT spins between 3 and 6 PM and you can
decode the telemetry easily with a pen and paper to see what it is currently
doing. http://aprs.org/psat.html

Even if a satellite did not spin at all, it would still rotate relative to
you almost 180 degrees from horizon to horizon.   Bob, WB4aPR

-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Ken
Alexander
Sent: Thursday, June 02, 2016 7:29 PM
To: Bob
Cc: AMSAT-BB
Subject: [amsat-bb] Does SO-50 Tumble? Was: "Polarization"

So far, I am only active on SO-50 and I have to say I’m impressed with the
reception quality with my TH-D72A and Arrow antenna.  The Arrow requires
only a twist to peak the signal to very good levels.  I’m starting to notice
a pattern where certain polarization angles produce the best results at
different times during a pass.  It would be interesting if this turned out
to be repeatable…and it leads to my next question:  How much (if at all)
does SO-50 or any other satellite tumble during its orbit?  I am assuming
that the current breed of ham satellites aren’t large enough to house motors
or other devices to control their attitude, which makes me think they must
tumble somewhat.

Once again, thank you all for your forbearance as I mine your collective
knowledge to bring myself up to speed!

73,

Ken Alexander
VE3HLS

> On May 31, 2016, at 1:51 PM, Bob <WB4SON at gmail.com> wrote:
>
> "The antennas I see in the photos of satellites we work are whips. Is the
> polarization becoming "circularized" as it re-enters earth's atmosphere or
> something?"
>
> Yep, that is exactly what is happening.  It is called Faraday Rotation,
> and as the signal from the satellite passes through the ionosphere, all
> sorts of polarity changes can and do happen. A linear polarized satellite
> antenna (horizontal or vertical) can appear to be the opposite or
> somewhere in between.  That's why folks rotate their Arrow or Elk
> antennas -- trying to match the polarity.
>
> Using a circular polarized antenna helps a bunch -- it doesn't matter what
> the polarity of the linear satellite antenna happens to be at any moment
> in time.
>
> But there is no free lunch -- Even a circular polarized antenna might need
> to be switched from Right Hand Circular Polarization (the default) to LHCP
> from time to time depending on what nasty thing the ionosphere is doing at
> any given moment.  Changing the polarity switch might bring a S0 signal up
> to S5, a 30 dB improvement.  I had that happen to me during a recent ARISS
> contact.
>
> 73, Bob, WB4SON
>
>
>
> On Mon, May 30, 2016 at 8:25 PM, Doug Andrews <dougg27 at hotmail.com
> <mailto:dougg27 at hotmail.com>> wrote:
>
>
> I too have wondered about this.
> I have not had much trouble hitting SO-50 and some success on AO-85 with a
> 5 watt handheld and arrow antenna without turning it. Worth a try.
> DougKG7UNU
>
>
>
> Sent from my Sprint Samsung Galaxy® Note 4.
>
> -------- Original message --------
> From: Ken Alexander <k.alexander at rogers.com
> <mailto:k.alexander at rogers.com>>
> Date: 5/30/16  4:41 PM  (GMT-08:00)
> To: amsat-bb at amsat.org <mailto:amsat-bb at amsat.org>
> Subject: [amsat-bb] Polarization
>
> I clipped this from another message because I didn't want to drag the
> discussion off course.  It's a question I've been wondering about
> since getting into this a few short weeks ago.
>
> I've also read (but haven't tried yet) about the trick of rotating the
> antenna 90 degrees on transmit, once you've established the best
> receive orientation.
>
> 73 de Bill, KG5FQX
>
> So far, with SO-20 I have rotated my Arrow antenna for best reception
> of the downlink and don't think I've had too much trouble being heard.
> At the same time I have wondered whether I should twist the antenna
> when transmitting to orient the 2m elements to give the same
> polarization as in receive. I don't know if this is a good idea or
> not, and frankly I have enough trouble remembering calls and grids,
> tracking the satellite, adjusting frequency and switching back to the
> correct VFO to worry about one more thing.
>
> I've seen that some commercial OSCAR antennas use circular polarization.
> The antennas I see in the photos of satellites we work are whips. Is
> the polarization becoming "circularized" as it re-enters earth's
> atmosphere or something?
>
> Comments and observations would be most welcome!
>
> 73,
>
> Ken Alexander
> VE3HLS, FN03
>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org <mailto: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
> <http://www.amsat.org/mailman/listinfo/amsat-bb>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org <mailto: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
> <http://www.amsat.org/mailman/listinfo/amsat-bb>
>

_______________________________________________
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