[amsat-bb] Re: New Satellite Downlink?

charlie Cantrill ki4rdt at yahoo.com
Wed Aug 25 18:00:35 PDT 2010

Would it be possible to allow students/hams around the world to send a text message to ground stations? This would be especially handy to those students/instructors who cannot send APRS packets to sats to generate interest and outreach. What about adding this feature in addition to sending bulletins of satellite users interest.

Charlie CantrillKI4RDTInstructor, Nelson County Area Technology Center

Date: Wed, 25 Aug 2010 12:27:00 -0400
From: "Robert Bruninga" <bruninga at usna.edu>
Subject: [amsat-bb]  New Satellite Downlink?
To: <amsat-bb at amsat.org>
Message-ID: <3DEE29EBEB7F407C97AFEA744C8B95D5 at ewlab.usna.edu>
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Possible new AMSAT Application?

We may have access to two old TRANSIT navigation satellites with
a 50 baud downlink at 149.985 (and 400 MHz). (presently coming
over in the mid afternoon).  My problem is, coming up with any
meaningful application to use them for communications that would
capture the interest of students, hams or volunteers in support
of education, public service or emergency comms or just plain

The downlink can be heard on an OMNI antenna (though I would
suggest a 3/4 wave (55") vertical) and could be decoded by a
simple software only application with a sound card. (someone has
to write it)...

The total useful message capability is about 500 bytes
transmitted every 2 minutes (at 50 baud).  The uplink is very
specialized and can ONLY BE DONE from one (or two) very special
commmand stations.  These satellites of course were the original
Navy Navigation satellite system (also called OSCARS) and so the
message would be in-place of the normal navigation data.  SO in
a sense, this is a downlink BROADCAST application.  Since ham
radio is two way, I'm stumped for applications.

The total message capability of 500 Bytes can contain one long
ARRL bulletin, or 20 APRS position/status reports, or say 20 or
so APRS text messages, or say 50 "callsign exchanges" or maybe
even 1 thumbnail image...  but what's the application?

Even if we allow say, INTERNET link to the command station for
"anyone" to contribute to the twice per-day upload, then
everyone's receiver application can receive them...  For what?

So Im looking for ideas.  All I can come up with so far is:
1) ARRL Bulletins? (I don't even know how often ARRL sends
2) Navy/Army/AF MARS broadcast bulletins...
3) Internet message in-to-command-upload-to message RF downlink.
Two stations do this to each other and it counts as a two-way
4) ...

Every scenario of interest usually begins with the much higher
value of UPLINK from the individual field station, not
downlink.. Hence I am stumped.

HUMMH... Maybe purely educational?  If the software can run on
any PC with a sound card connected to any scanner... Then every
school can use it as a satellite downlink signal of interest..
What kind of thumbnail image can fit in 500 bytes?  Send in your
picture and get it downlinked on a given day?


Will need a DSP volunteer to write the sound card decoder.  



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