[amsat-bb] Re: New Satellite Downlink?

jon jon at kenneke.com
Wed Aug 25 14:31:02 PDT 2010

Assuming TRANSIT uses an 8-bit byte, then it has the capability of sending 
4,000 different messages (one for each bit). Probably would want some 
checksum, so the total different messages would be less.

Hmmmm, with 3000+ message choices, there might be some good use.

Regional weather warnings? Status of 3000 different "stations"?

I actually had a TRANSIT receiver several years ago. It would still lock 
onto the satellites, but the navigation information is no longer valid. 
Bob is right: all it took was simple vertical to receive it.

For folks that don't know, TRANSIT was the one of the first satellite 
navigation system. It was a GPS of sorts.

I've done DSP soundcard coding before. Years ago I wrote a DGPS decoder, 
so if you need some more coders, I'd be happy to help.


On Wed, 25 Aug 2010, Robert Bruninga wrote:

> 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
> fun...
> 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
> bulletins...)
> 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
> QSO?
> 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?
> Etc..
> Will need a DSP volunteer to write the sound card decoder.
> Bob, WB4APR
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