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
