[amsat-bb] Re: New Satellite Downlink?
andres at msu.edu
Wed Aug 25 14:58:23 PDT 2010
Heh. One of the escape sequences could be which language to use,
so with the 16-bit scheme here, you could have 64K possible ones
to choose from. Just have a 65,000 word table for each one.
You'd send out messages one language at a time.
On Wednesday 25 August 2010 17:55:09 Graham Shirville wrote:
> 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.
> > _______________________________________________
> > Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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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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