Model Specific Notes - pavolgaj/radiosonde_auto_rx GitHub Wiki

This page provides information for specific radiosonde models.

Graw DFM-06 / DFM-09

These sondes are known to drift in frequency throughout their flight. This may cause auto_rx to lose lock on the signal, or sometimes detect a single radiosonde on adjacent 10 kHz channels.

The use of the newer experimental decoders (which have better drift handling ability) may assist with decoding of these sondes.

Intermet iMet-1 / iMet-4

iMet sondes do not transmit their serial number within their telemetry packets. This makes life somewhat difficult, as we need a unique identifier for the various mapping systems (sondehub.org / APRS / Chasemapper) to be able to distinguish between different radiosondes, and for multiple stations to contribute positions for the same radiosonde.

As a way around this issue, auto_rx generates a unique ID for each received iMet sonde by using:

• The reported time and telemetry sequence number to calculate the power-on time of the sonde;
• and the transmit frequency of the sonde, quantised to the nearest 100 kHz.

These two bits of information are concatenated, and a SHA256 hash is calculated. The last 8 characters of the hash are used for the Sondehub ID, and the last 5 for the APRS callsign. The code that calculates the ID is available here.

Warning - iMet-1 sondes increment their frame counter twice every second, vs once per second for iMet-4 sondes. This needs to be detected and compensated for when calculating the power-on time. Refer here for the algorithm used.