I'm working on a return-to-launch high altitude glider (balloon launched). My radio system needs to be able to communicate at 100km or more. My current plan is to use an FRS radio. This radio is modified to work on the 70cm ham band, and should be able to put out 1 or 2 Watts. I'll have a 1/4 wave ground plane antenna on the glider and a 6-10 dB yagi at the ground station. I won't be sending much data. Mostly just position updates from the glider to ground. Does this sound like a workable solution?
BTW, one of my goals is to keep this project very low cost, which is why I want to use the FRS radio. It's already modified and legal for ham use, and I will be attempting some long range tests. It's hard to simulate a 60,000 ft antenna, though!
Use HF attenuator for distance simulation. Calculate Free Space Loss and define your fade margin. If you don't want to buy attenuator (dB=Free Space Loss + Fade Margin), you can build your own easily (e.g http://openbsc.osmocom.org/trac/wiki/10db_attenuator).