I'm the NOAA engineer who wrote SkySonde, thanks for the mention. Those looking to try the software can download it from here, along with several other weather balloon tools (note that SkySonde only works with Intermet iMet radiosondes and attached ozone/water instruments):
The availability of these tools to the general public does not condone attempts to recover balloon payloads that land on private property, government property, or hazardous locations. Predicted trajectories and landing zones are only approximate, therefore active tracking is required to accurately locate launched payloads.
Here is SkySonde Server receiving raw radiosonde telemetry using the SDRplay RSP2:
iMet radiosondes are typically used at 401-405 MHz depending on their configuration.
SkySonde Client connects to the server to display, plot, and output balloon data as it comes in:
We have a lot of users/technicians in the field unfamiliar with software-defined radio. Walking them through the complexities of SDR Uno / SDR# / HDSDR would be far too difficult, so I decided to write a custom FM receiver directly into my existing SkySonde balloon telemetry software. I wrote it in C# and communicate directly with the driver API to receive I/Q samples at 2 MHz. After some filtering and decimating, I use an FM discriminator to convert I/Q into audio, then filter and decimate some more before passing the result to a software comparator and UART that decodes the Bell 202 signal and assembles full byte frames. Once a complete data packet is received, it is also CRC checked before being used.
This has been very successful. I received a balloon 318 km away with the RSP2 attached to a yagi with preamp, where our old system cut out at 156 km on the same flight. And the RSP2 would have received it longer if the battery on the radiosonde hadn't died.
Here is the basic setup:
Just one cable between each part thanks to the bias tee power for the preamp. The software download webpage I linked has specifics on parts if anyone is interested.
SkySonde also supports RTL-SDR dongles if you manually download the 32-bit rtlsdr.dll from osmocom and move it to the install directory (can't include it directly due to licensing issues). They perform surprisingly well for being cheap, I've received full balloon flights with them too. But they are a lot flimsier compared to the nice RSP2 pro with the aluminum enclosure, and don't have the same gain options and ADC quality.
Here is my coworker launching one of our balloons south of Boulder, CO, USA: