[amsat-bb] [Video] HuskySat-1 decoded with manual tuning and no SDR

[Chris Thompson]

Nice video.  Thanks for posting.  As Zach said, the spinning phasor tells
us that the frequency is not locked, but that is OK as long as it is a
line.  The "Dot Product" decoder is not a coherent decoder so it is not in
phase lock with the original carrier.  The phasor is allowed to rotate and
we will still get 100% decode.  It can't be a circle or a cloud though :).

If you use the Costas loop decoder then it will freeze the phasor
horizontally when locked because it is a coherent decoder.  The two
decoders have pros and cons with their ability to decode.  Enjoy exploring
that.

73
Chris

On Sun, Feb 2, 2020 at 9:10 PM John Brier via AMSAT-BB <amsat-bb at amsat.org>
wrote:

> Thanks Zach.
>
> I noticed the spinning too, and noticed it was not what others have shown
> in their videos, so figured it had to do with my manual tuning, so thanks
> for verifying.
>
> I read the first page and that doc looks like a really good primer on
> digital RF. Some of those diagram might as well be art.
>
> 73, John Brier KG4AKV
>
> On Sun, Feb 2, 2020, 20:44 Zach Metzinger via AMSAT-BB <amsat-bb at amsat.org
> >
> wrote:
>
> > On 02/02/20 18:50, John Brier via AMSAT-BB wrote:
> > > One thing I didn't mention in the video, at the end of the pass around
> > > 10 degrees elevation and lower I decoded a lot of frames because the
> > > signal was still strong and by that point the frequency wasn't
> > > changing much anymore, as the satellite's relative speed stopped
> > > changing.
> >
> > The video is instructive as one can see the plotted constellation
> > "spinning" before symbol lock. Even after locking, the constellation
> > rotates, indicating a frequency error between the transmitter and
> > receiver presenting itself as a continuous phase rotation.
> >
> > With an antipodal signal, the constellation diagram will tell you a lot
> > about received signal quality, including SNR (fuzzy points), interfering
> > signals (donuts), out-of-lock (one big circle), frequency/phase errors
> > (smeared clusters of points in a radial pattern).
> >
> > A great technical read on vector modulation analysis:
> >
> > http://literature.cdn.keysight.com/litweb/pdf/5091-8687E.pdf
> >
> > --- Zach
> > N0ZGO
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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.
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-- 
Chris E. Thompson
chrisethompson at gmail.com
g0kla at arrl.net