The reason I asked is because I am part of
ANSR. I use my airplanes to assist in the recovery of the balloon payloads after they come down under parachute using APRS (
our last flight) or airborne transmitter hunting. Our last few flights have gone to over 100,000 ft.
ANSR is staffed with hams, so we have been (legally) using the 2meter and 440MHz bands for downlink telemetry, video, and recovery beacons. A 1 Watt VHF transmitter at 100,000ft over Arizona can be received from California to Kansas.
I would encourage you to get to know some hams in your area, and to get a ham license of your own. Write back if I can assist...