I was involved in such a fun weather balloon experiment about 25 years ago. It would transmit on 144 MHz in human speech: the time since lift off, altitude, rate of ascent, temperature inside and outside the pod. The power output was only about a hundred milliwatts FM, but the signal from central Victoria could be picked up from Queensland and South Australia. We discovered a temperature inversion layer as the balloon went up. It was launched on a hot day, but the temperature got down to -45 deg C, but at its maximum altitude it increased to -30 deg C.
The balloon was launched in Shepparton, got to an altitude of 65,000 feet before it burst over Wangaratta (where I lived at the time), and somehow found its way to the Tumbarumba Forest, where it was awaiting for a generous cash prize for the ham to found it.
These days, life is a lot more easy. GNSS receivers cost little and weigh nothing, there is much easier and more powerful technology around and better sensors. I would like to do a balloon experiment again in a year or two. With a camera.