Meteor-M2 series demodulator
This is a free, open-source LRPT demodulator for the Meteor-M2 Russian weather satellite series. It supports reading from a I/Q recording in .wav format, and it outputs an 8-bit soft-QPSK file, from which you can generate an image with the help of LRPTofflineDecoder, meteor_decode or medet.
Features:
- Support for regular (72k,
-r 72000) and interleaved (80k,-r 80000) modes - Support for QPSK and OQPSK modulation schemes
- Can read samples from stdin (pass
-in place of a filename) - Can output samples to stdout (
--stdout, disables all status indicators)
Compiling and installing
mkdir build && cd build
cmake ..
make
sudo make install
If you don't need the fancy ncurses interface, you can disable it at compile
time by running cmake -DENABLE_TUI=OFF .. when configuring.
Usage info
Usage: meteor_demod [options] file_in
-B, --batch Disable TUI and all control characters (aka "script-friendly mode")
-d, --freq-delta <freq> Set the maximum carrier devation to <freq> (default: +-3.5kHz)
-m, --mode <mode> Specify the signal modulation scheme (default: qpsk, valid modes: qpsk, oqpsk)
-o, --output <file> Output decoded symbols to <file>
-q, --quiet Do not print status information
-r, --symrate <rate> Set the symbol rate to <rate> (default: 72000)
-R, --refresh-rate <ms> Refresh the status screen every <ms> ms (default: 50ms in TUI mode, 2000ms in batch mode)
-s, --samplerate <samp> Force the input samplerate to <samp> (default: auto)
--bps <bps> Force the input bits per sample to <bps> (default: 16)
--stdout Write output symbols to stdout (implies -B, -q)
-h, --help Print this help screen
-v, --version Print version info
Advanced options:
-b, --pll-bw <bw> Set the PLL bandwidth to <bw> (default: 1)
-f, --fir-order <ord> Set the RRC filter order to <ord> (default: 32)
-O, --oversamp <mult> Set the interpolation factor to <mult> (default: 5)
Advanced options explanation
-b, --pll-bw: higher = potentially faster carrier acquisition, but worse tracking performance if the signal is weak. Does not affect CPU usage.-f, --fir-order: higher = more accurate signal filtering, but higher CPU usage. 16-32 is a good range, above 64 is most likely overkill.-O, --oversamp: higher = more accurate symbol timing recovery, but higher CPU usage. Can be reduced if input sampling rate is high, although it's more efficient to use a low sampling rate and a high oversampling value than vice-versa.
Live demodulation
Starting from v1.0, you can live demodulate on a toaster if that's your thing (~35% peak CPU usage on a Raspberry Pi Zero):
rtl_sdr -s 230000 -f 137.1M -g <gain> -p <ppm> - | meteor_demod --bps 8 -s 230000 -B -
If you want to see the constellation diagram while demodulating live:
mkfifo /tmp/raw_samples
meteor_demod --bps 8 -s 230000 /tmp/raw_samples &
rtl_sdr -s 230000 -f 137.1M -g <gain> -p <ppm> /tmp/raw_samples
rm /tmp/raw_samples
With a decoder that supports reading symbols from stdin, you can even decode live (~75% peak CPU usage on a Raspberry Pi Zero):
rtl_sdr -s 230000 -f 137.1M -g <gain> -p <ppm> - | meteor_demod --bps 8 -s 230000 --stdout - | meteor_decode -o live.bmp -