- Decoder is based on zilog80 Vaisala RS41 decoder https://github.com/rs1729/RS/
- Using same header as RS41 for NRZ, for Manchester use extended header Manchester header (similar to DFM)
- File > Encoder > Transmission line + noise > Decoder > File
- Eg. Arduino > RF modulator from STB > Transmission line + noise > RTL-SDR > Decoder > collectd > RRD Graphs
- Eg. RS41 radiosonde > Transmission line + noise > RTL-SDR > nrz-audio-modem
- Manchester from NRZ is coded like: 01->1,10->0 , Maybe it is inverted if my system use little endian byte order. (I'm not sure now.)
Frame structure for speed 4800 baud/s, 16 user bytes => total 26 bytes (HEAD+DATA+CRC).
- NRZ coding:
HEAD = "0000100001101101010100111000100001000100011010010100100000011111"
/--------------*-------------------------*-----------------------\
| HEAD 64 bits | NRZ coded DATA 128 bits | NRZ coded CRC 16 bits |
\--------------*-------------------------*-----------------------/
Total: 208 bits -> 26 bytes
- Manchester coding:
HEAD = "0101100110011001100110011001100110010101101101101010101010101010"
/--------------*--------------------------------*------------------------------\
| HEAD 64 bits | Manchester coded DATA 256 bits | Manchester coded CRC 32 bits |
\--------------*--------------------------------*------------------------------/
Total: 352 bits -> 44 bytes
Support for following RS codes:
- RS(255,247)
- RS(255,239)
- RS(255,231)
- RS(255,223)
- RS(255,215)
- RS(255,207)
Reed-Solomon coder and decoder is taken from https://github.com/supurloop/ssf. Galois Field GF(2^8). Maximum RS block size is 255 bytes (message + parity).
- Decoder
Audio NRZ/Manchester decoder
Usage: ../decoder/decoder -i <filename> [-o <filename> -IRA -b <rate> -M -L <frame length> ] -F <RS level> | -h
-i <filename> Input 8 or 16 bit WAV file
-i - Read from stdin
-o <filename> Output data file
-o - Write to stdout
-b <rate> Signal baud rate, default 4800
-L <frm len> Set usefull data lenght in bytes, default 246 bytes, minimum 8
-F <RS level> Check Reed-Solomon parity bytes: 0 = uncoded (default), 1 = (255,247), 2 = (255,239)
3 = (255,231), 4 = (255,223), 5 = (255,215), 6 = (255,207)
-M Use Manchester coding, default is NRZ
-I Inverse signal
-R Better bit resolution
-A Average decoding
-P <mode> Frame printing mode number
0 - HEX frame output, default
1 - Decoding from STM32 bluepill test
2 - Decoding from Vaisala RS41
3 - Decoding from Vaisala RS41 sounding sonde
-h Show this help
Build: 21:21:53 Sep 10 2021, GCC 5.3.0
Run:
sox -t pulseaudio default -t wav - 2>/dev/null | ./decoder -i -
Decoder is under test with STM32 Blue pill board and Si5351 transmitter
- Encoder
Audio NRZ/Manchester encoder
Usage: ./encoder -o <filename> [-i <filename> -b <rate> -w <rate> -M -R -L <frame length>] -F <RS level> | -h
-i <filename> Data file to read
-i - Read from stdin
-o <filename> Output WAV file
-o - Write to stdout
-b <rate> Signal baud rate, default 4800 bit/s
-L <frm len> Set usefull data lenght in bytes, default 246 bytes, minimum 8
-F <RS level> Add Reed-Solomon parity bytes: 0 = uncoded (default), 1 = (255,247), 2 = (255,239)
3 = (255,231), 4 = (255,223), 5 = (255,215), 6 = (255,207)
-M Use Manchester coding, default is NRZ
-R RAW output
-w <rate> WAV file sample rate, default 24000 Hz
-h Show this help
Build: 21:17:30 Sep 10 2021, GCC 5.3.0
Run:
./encoder -o - -b 4800 -w 44100 | sox --ignore-length - -t wav - fir gauss2.4.txt | play -t wav -
- Implement Manchester code => Finished
- Add Reed Solomon ECC => Finished
- Better header detection
- Create some Arduino encoder sketch sending small data packet (like temperature) => Finished https://github.com/tom2238/radiosonde_hacking/tree/main/rs41
- Some bugs and features :-)
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