hf digital modes

I'm looking to acquire or somehow build an ultra portable HF sms text messaging radio for when I'm out in the back country. I only need to transmit to the nearest iGate to send the APRS SMS text message. The radio will be stowed away in a backpack and only used to check-in back home once a day...

Last night, I was scanning through HF and kept hearing what sounded like 850-hz RTTY. It must have been on 10-12 different frequencies. I think I heard it on 3.925 and 6.750, but whenever I try to decode it I can never seem to decode it. I have tried MixW and Fldigi. I was connected online...