> 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.
I'm embarassed that I still have not heard the bird on 2 tries. Its supposed to be on 149.987 MHz and you can hear it's 2.3 KHz tone with an FM receiver... I did hear it on APL-JHU's system also consisting of an amateur OSCAR class station... But not on mine yet.... OOPS! Wait! I have a very sharp DCI BANDPASS filter up there! Duh.... Ill try a different antenna this time! OK, the signal is 50 baud modulated with + and - 60 degree phase shift on the 400 MHz carrier (it can be switched to the 149.987 MHz carrier, but is not there currently). The wave form of the modulation is as follows: To transmit a "1" the carrier is phase shifted +60 degrees for about 2 ms, then shifted -60 deg for about 2 ms and then brought back to carrier with no phase shift for about 6 ms, then it is shifted - 60 deg again for 2ms and then +60 for 2ms and then brought back to no shift for another 6 ms. The "0" is the opposite pattern of shifts. This process provides a clock signal at twice the bit rate. The actual exact period of each symbol is 19.7 ms. The beginning of each exact 2 minute (6103 bit block) is marked with 0111111111111111111111110, that is 23 "1"'s with a leading and ttrailing zero. Bob, Wb4APR > 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 > > > > _______________________________________________ > > 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
