[amsat-bb] PSAT key to success

Robert Bruninga bruninga at usna.edu
Sun May 31 22:56:04 UTC 2015

Until we get authors adding Full duplex and AFC to their PSK31, here is a
scheme that will work.

Focus on the OVERHEAD pass.  Horizon to Horizon.  Because during these
passes, the satellite is coming right at you for the first 5 minutes, and
directly away from you for the next 5 minutes.  This means the Doppler is
nearly constant high during the first 5 minutes and then a rapid shift to
a constant LOW for the last 5 minutes.  And horribly shifting for the
middle 1 minute.

Your signal will have very little Doppler on the downlink and most anyone
with any kind of PSK31 decoder will decode you fine.

Don't do any frequency transmitteirn shift on the uplink  or as KO6TZ
says, you will cause people to lose lock..

When the satellite crosses overhead, you can then shift your TX frequency
UP by 1.15 KHz and people will see you more or less back where you
started... maybe.

Bob, Wb4aPR
-----Original Message-----
From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of KO6TZ Bob
Sent: Sunday, May 31, 2015 4:39 PM
To: amsat-bb at amsat.org
Subject: Re: [amsat-bb] PSAT 1925 pass

 >Some of the traces I watched were pretty horribly Doppler shifted and
not sure if MixW is able to decode that  >coming up from ten meters and
drifting like the ones I sw.

 From me experience on DO-64 and FO-29 using PSK31/63,  I found adjusting
for Doppler on the SSB up-link is a double edged sword.

When the frequency is updated for Doppler, you loose sync for a few
characters.  If you don't correct the frequency, you will exceed the AFC
limit of most programs, except  WINPSK.

  WINPSK doesn't support multi line copy.  Also using DigiPan in "munti"
mode, there is no AFC.  The s/w just creates another line.

Pick your poison.....

KO6TZ   Bob

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