PSK31 is 31 bps, but that's with ~100 Hz between channels. DXing is common in the 14 MHz band, so you could probably get to the megabits-per-second range befor

PSK31 is 31 bps, but that's with ~100 Hz between channels. DXing is common in the 14 MHz band, so you could probably get to the megabits-per-second range before Physics (or the FCC) stops you.