[amsat-bb] Re: New Satellite Downlink?

Graham Shirville g.shirville at btinternet.com
Wed Aug 25 14:55:09 PDT 2010

Hi Steve,

I wonder how that would work with multiple languages:)


Graham G3VZV
----- Original Message ----- 
From: "STeve Andre'" <andres at msu.edu>
To: <amsat-bb at amsat.org>
Sent: Wednesday, August 25, 2010 10:24 PM
Subject: [amsat-bb] Re: New Satellite Downlink?

> On Wednesday 25 August 2010 12:27:00 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.
> Well, I'm not sure how many applications there are for this, but it
> could be fun to try some stuff.
> Way way back hundreds of years ago in the 70's I wrote some code
> to take English text and crunch it down and transmit it over a modem.
> I won't say the following is reasonable, but at 50 baud the little link
> needs all the help it can get. ;-)
> A lookup table can be made for about 65,000 of the most commonly
> used words plus various technical stuff.  A message can then it
> converted into a series of 16-bit offsets into the table of words,
> taking 2 bytes (octets) per word.  Printing out words takes the
> stream of data, does a lookup for each 16-bit quantity, prints
> that word plus a space, and goes on.
> A word like "communications" which is 14 bytes becomes two and
> is thus a win, but "a" "I" and the like is a loss.  There could be an
> escape sequence to provide for the literal transmission of a word
> not in the 65,000 lookup table, and one could also be added for
> upper casing of the next word, etc.
> Doing this, you can transmit 250 words from the lookup table
> each minute, fairly faster than squirting out raw ASCII.
> Since you'd likely need a decoder no matter what the transmission
> is, the 65,000 word table is stored on the client side.  Hilarity
> will probably ensue when someone doesn't update their table
> after a big change, and gets slightly demented messages till
> they update their code.
> Thinking about what to transmit...  Possibly space weather
> transmissions?  CMEs and such are something that has world
> wide impact.
> Well, that, or national lottery scores.
> -- 
> STeve Andre'
> wb8wsf  en82
> Disease Control Warden
> Dept. of Political Science
> Michigan State University
> A day without Windows is like a day without a nuclear incident.
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