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.
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...
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