From company website:
The state-of-the-art DFM-09 is one of the lightest and smallest radiosondes on the market and is also one of the most used radiosondes in the world. It was designed for precise and reliable measurement of temperature, humidity, air pressure, wind direction and wind speed. It is easy to use, making it the ideal instrument for daily sounding.
400.01 MHzMegaHertz (MHz) 10^6 Hz to 405.99 MHzMegaHertz (MHz) 10^6 Hz with 20kHz channel spacing
Output power: P = 100 mW ERP or 20 dBm
Antenna: Quarter wave vertical monopole
Coding: Digital bi-phase Manchester
Transmission rate: 1250 baudBaud (unit symbol Bd) is the unit for symbol rate or modulation rate in symbols per second. in a time-slot of 57.6ms
Transmission rate of GPS data in 4 time-slots of 166.4 msmilliseconds (.001 of a second) (224ms - 57.6 msmilliseconds (.001 of a second) = 166.4 msmilliseconds (.001 of a second)); The transmission of the GPS-data is done in the background during the TU-measurement. One complete set of GPS data is transmitted per second in addition to the TU-transmission
Error correction: 4 bits are expanded to 8 bits to correct one error and detect two errors. Additionally, data are interleaved over 7 bytes.
Opensource SDR based decoding software with web interface https://github.com/projecthorus/radiosonde_auto_rx