[amsat-bb] Re: All Satellites (Alan P. Biddle)
FDMDV uses a 1400 bps codec, occupies only 1100 Hz and operates with any SSB transceiver. Comunications doesn't have to be full duplex. At 12-16 kbps the satellite and ground stations could alternate with short bursts of voice or text. This wouldn't fit in a 2.4 kHz SSB bandwidth but would require a 16-20 kHz wide filter or use of a transverter and a simple SDR radio like the SoftRock. 73, John KD6OZH - Original Message - From: Gordon JC Pearce gordon...@gjcp.net KD6OZH's mentioning of a 1200 bps voice codec is very interesting, too. I see that DSTAR's AMBE is down to 2000 with error correction, and Speex operates down to 2000, too, though I think without error correction. (I find the latter much more engaging as a ham, since it is open source.) It would be a hoot to do a voice conference over the Internet using a sample of low bitrate codecs and just get a sense of what might be possible. One downside of voice is that it would occupy the transponder far more than messaging, and Bob's favorable power calculations would need to be estimated downwards. Would the packet satellite be capable of bent-pipe operation though? You'd need to transmit and receive simultaneously to get that working. I'd far prefer to use Speex rather than the locked-down proprietary AMBE codecs. ___ 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
[amsat-bb] Re: All Satellites (Alan P. Biddle)
On Fri, 2009-09-25 at 22:19 -0400, Robert Bruninga wrote: At a SmallSat conference... this summer, I was amused at the casual assumption by a researcher that 50, cubesats could be launched as part of an upper atmosphere project using ham frequencies for the downlinks. And wouldnt it be a hoot if everyone of them could put their RX/TX into a bent-pipe packet mode, and then we would have amateur radio global hand-held text messaging satellite system... (They would have a lifetime of only 3-4 months.) But it would be FUN for a while! Using some of the 2-way very small micro APRS packet systems, a 2 to 5 Watt transponder will easily fit on a singl circuit card in a small cubesat. See www.aprs.org/cubesat-comms.html Bob, WB4APR If you could have maybe five or six cubesats with an FM transponder orbiting in such a way that there was a good 15-minute pass every hour, then I suspect that would work wonders for getting people interested in satellites again. The technical requirements for getting into them would be low enough for entry-level amateurs all over the world to have a crack at them - dual-band HT and a homebrew Arrow clone, and you're good to go. Cheap, simple satellites, and cheap, simple ground stations. How many could you fly for the cost of one HEO sat and launch? Gordon MM0YEQ ___ 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
[amsat-bb] Re: All Satellites (Alan P. Biddle)
And wouldn?t it be a hoot if [these cubesats] could put their RX/TX into a bent-pipe packet mode, and then we would have amateur radio global hand-held text messaging satellite system... Using some of the 2-way very small micro APRS packet systems, a 2 to 5 Watt transponder will easily fit... in a small cubesat. See www.aprs.org/cubesat-comms.html If you could have maybe five or six cubesats with an FM transponder... [with] a good 15-minute pass every hour... would work wonders for getting people interested in satellites again. ... [with a] dual-band HT and a homebrew Arrow clone The beauty of the APRS packet text-messaging relay cubesat is that it can have a 10 times higher power transmitter compared to an FM voice transponder for the same average power budget. This makes it workable on an HT with just a whip antenna, instead of needing a handheld beam. Plus, each message takes one second instead of 15 for each QSO. So that is why I prefer handheld packet text messaging as a cubesat mission. Ten times the downlink power budget and 15 times the number of contacts per pass. AO51 downlink could be 10 times as strong if the transmitter would just drop when not in use... 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
[amsat-bb] Re: All Satellites (Alan P. Biddle)
The 1200 bps Pacsats used an uncoded BPSK downlink on 70 cm and worked fine with 1/4-wavelength vertical antenna on the ground. As I remember, they only generated 1 watt of RF. A 2-meter downlink using an error correcting code would give 4 times the data rate with the same power. Digital voice now fits in 1200 bps so you could support APRS plus multiple voice channels. 73, John KD6OZH - Original Message - From: Robert Bruninga bruni...@usna.edu To: amsat-bb@amsat.org Sent: Sunday, September 27, 2009 14:42 UTC Subject: [amsat-bb] Re: All Satellites (Alan P. Biddle) And wouldn?t it be a hoot if [these cubesats] could put their RX/TX into a bent-pipe packet mode, and then we would have amateur radio global hand-held text messaging satellite system... Using some of the 2-way very small micro APRS packet systems, a 2 to 5 Watt transponder will easily fit... in a small cubesat. See www.aprs.org/cubesat-comms.html If you could have maybe five or six cubesats with an FM transponder... [with] a good 15-minute pass every hour... would work wonders for getting people interested in satellites again. ... [with a] dual-band HT and a homebrew Arrow clone The beauty of the APRS packet text-messaging relay cubesat is that it can have a 10 times higher power transmitter compared to an FM voice transponder for the same average power budget. This makes it workable on an HT with just a whip antenna, instead of needing a handheld beam. Plus, each message takes one second instead of 15 for each QSO. So that is why I prefer handheld packet text messaging as a cubesat mission. Ten times the downlink power budget and 15 times the number of contacts per pass. AO51 downlink could be 10 times as strong if the transmitter would just drop when not in use... 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
[amsat-bb] Re: All Satellites (Alan P. Biddle)
On Sun, 2009-09-27 at 16:02 -0300, Bruce Robertson wrote: In a recent conversation on this list, I did the math and conservatively estimated that 125 1U cubesats could be launched for the current quoted price of a HEO launch alone. I think Bob Bruniga mentioned something like $400 to build a packet satellite. If that's correct - $400 per unit - then I will split in $100 to get the first one started (and more, if the exchange rate swings in my favour again). The problem, as I think Bob has noted before, is momentum: a constellation of these is very useful; one of them is much less so. The group that puts up the first of them, then, is not doing much of interest and hopes that others will follow to increase the 'network effect'. For this reason, we cannot expect (most) university cubesat missions to look merely like this, unless their institution has a special interest in emergency communications, as Bob's uniquely is. I personally have no interest in emergency comms, but I would like to see useful packet satellites. If they're that cheap to build, then we should have a big stack of them ready to fly. KD6OZH's mentioning of a 1200 bps voice codec is very interesting, too. I see that DSTAR's AMBE is down to 2000 with error correction, and Speex operates down to 2000, too, though I think without error correction. (I find the latter much more engaging as a ham, since it is open source.) It would be a hoot to do a voice conference over the Internet using a sample of low bitrate codecs and just get a sense of what might be possible. One downside of voice is that it would occupy the transponder far more than messaging, and Bob's favorable power calculations would need to be estimated downwards. Would the packet satellite be capable of bent-pipe operation though? You'd need to transmit and receive simultaneously to get that working. I'd far prefer to use Speex rather than the locked-down proprietary AMBE codecs. I guess another aspect of the cubesat approach is that the cost of failure is much lower. If a low bitrate audio codec doesn't really work well, it would be a less expensive enterprise and easier to chalk up to experience. You could also just blow new firmware on it remotely. If it bricked, that's a shame but at least you tried... Gordon MM0YEQ ___ 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
[amsat-bb] Re: All Satellites (Alan P. Biddle)
Bruce Robertson wrote: In a recent conversation on this list, I did the math and conservatively estimated that 125 1U cubesats could be launched for the current quoted price of a HEO launch alone. The more I think about this digital cubesat constellation proposal, the more I see its merits. I guess that would be if you had the slightest interest in digital satellite operation. Personally I have absolutely ZERO interest in digital satellite operation, only very little in the single channel FM birds, a lot more in linear LEO birds, and even more in linear HEO birds. For the most part, I don't care about DXing, but actually being able to talk to someone for more than a few minutes is rather nice. I will admit that I was happy to get Africa confirmed to complete my Satellite Worked All Continents a few years ago - only to have the ARRL lose the cards. -- 73 - Jim Walls - K6CCC j...@k6ccc.org Ofc: 818-548-4804 http://home.earthlink.net/~k6ccc AMSAT Member 32537 - WSWSS Member 395 ___ 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
[amsat-bb] Re: All Satellites (Alan P. Biddle)
At a SmallSat conference I attended on behalf of AMSAT this summer, I was amused at the casual assumption by a researcher that 50, Five Oh, cubesats could be launched as part of an upper atmosphere project using ham frequencies for the downlinks. (They would have a lifetime of only 3-4 months.) Jan King, W3GEY/VK4GEY, who does coordination of satellite frequencies, gently but firmly brought them down to earth a bit. On the one hand, we get new hams with interests in space communications from these projects, but on the other we need to prevent the de facto appropriation of needed frequencies. A fine line to walk. Alan WA4SCA The thing that worries me the most is that the de facto appropriation of our amateur satellite frequencies seems very likely if we continue along a path which keeps us from filling those slots with payloads of our own. All this complaining about cubesats and the use of amateur frequencies for telemetry is kind of pointless if we aren't using those frequencies and have no prospect of using those frequencies in the foreseeable future. It seems to me that coordinating 50 cubesats for four months could be a tractable problem, depending on the precise nature of the signals and their orbital spacing. It's not like there is a huge number of operational amateur satellites that they'd have to avoid. Mark K6HX ___ 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
[amsat-bb] Re: All Satellites (Alan P. Biddle)
At a SmallSat conference... this summer, I was amused at the casual assumption by a researcher that 50, cubesats could be launched as part of an upper atmosphere project using ham frequencies for the downlinks. And wouldnt it be a hoot if everyone of them could put their RX/TX into a bent-pipe packet mode, and then we would have amateur radio global hand-held text messaging satellite system... (They would have a lifetime of only 3-4 months.) But it would be FUN for a while! Using some of the 2-way very small micro APRS packet systems, a 2 to 5 Watt transponder will easily fit on a singl circuit card in a small cubesat. See www.aprs.org/cubesat-comms.html 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
