Hi Steve, I wonder how that would work with multiple languages:)
73 Graham G3VZV ----- Original Message ----- From: "STeve Andre'" <and...@msu.edu> To: <amsat-bb@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...@amsat.org. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via amsat...@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
