RS-tracker/dfm

Radiosonde DFM-06/DFM-09

Based on information already available at
https://www.amateurfunk.uni-kl.de/projekte-aktivitaeten/decoder-wettersonden/

Files

• dfm06ptu.c

Compile

gcc dfm06ptu.c -lm -o dfm06ptu

Usage

./dfm06ptu [options] <audio.wav>

• <audio.wav>: FM-demodulated signal, recorded as wav audio file
• options:
  -i: invert signal/polarity (DFM-09)
  -b, -b2: integrate rawbit-/bit-samples
  -r: output raw data
  -v: additional info
  --ecc: Hamming code error correction
  --ptu: temperature
  

Examples

• ./dfm06ptu --ecc --ptu -v dfm-audio.wav

FSK-demodulation is kept very simple. If the signal quality is low and (default) zero-crossing-demod is used, a lowpass filter is recommended:

• sox dfm-audio.wav -t wav - lowpass 2000 2>/dev/null | ./dfm06ptu --ecc --ptu -v

If timing/sync is not an issue, integrating the bit-samples (option -b2) is better for error correction:

• ./dfm06ptu -b2 --ecc --ptu -v dfm-audio.wav

For DFM-09 or if the signal is inverted (depends on sdr-software and/or audio-card/settings), try option -i.

Error correction

Use error correction --ecc together with option -b2. The codewords are 8-bit long and the [8,4] extended Hamming code can correct one-bit errors and detect two-bit errors. If there are more than two errors, it is possible that the codeword is corrected to a different codeword closer to the received word. The minimum distance is 4. Thus if the signal level is low, the decoding can go wrong. A high number of codewords with bit-errors in a frame could indicate unreliable decoding.