demod_fm

Command line utility based on liquid-dsp for demodulating SDR IQ streams. Firstly it was written in C (last commit to C version), however now it is rewritten in rust.

what the fork?

Additions

This fork adds the input and output support of:

• unsigned 8 bits integer (u8)
• signed 8 bits integer (s8)

u8 input format is useful to work with rtl_sdr recorded IQ files while s8 input format will be necessary to work with hackrf_transfer IQ recorded files.

dependencies

autoconf

sudo apt-get install autoconf

liquid-dsp

git clone git://github.com/jgaeddert/liquid-dsp.git
cd liquid-dsp
./bootstrap.sh
./configure
make
sudo make install
sudo ldconfig

rust

http://www.rust-lang.org/install.html

curl https://sh.rustup.rs -sSf | sh

build

git clone https://github.com/cdeletre/demod_fm.git
cd demod_fm
cargo build --release

install

mac os x

cp target/release/demod_fm /usr/local/bin/

linux

sudo cp target/release/demod_fm /usr/local/bin/

usage

play FM radio recording

Play FM radio recording (deemph filter not used and does not play in stereo)

cat testfiles/fm_radio_rds_228000sps_s8.iq | demod_fm --samplerate 228000 --intype s8 --outtype i16 --bandwidth 100000 fm --deviation 75000 | play -t raw -r 228000 -e signed-integer -b16 -c 1 -V1 -
cat testfiles/fm_radio_rds_228000sps_u8.iq | demod_fm --samplerate 228000 --intype u8 --outtype i16 --bandwidth 100000 fm --deviation 75000 | play -t raw -r 228000 -e signed-integer -b16 -c 1 -V1 -
cat testfiles/fm_radio_rds_228000sps_s16.iq | demod_fm --samplerate 228000 --intype i16 --outtype i16 --bandwidth 100000 fm --deviation 75000 | play -t raw -r 228000 -e signed-integer -b16 -c 1 -V1 -
cat testfiles/fm_radio_rds_228000sps_f32.iq | demod_fm --samplerate 228000 --intype f32 --outtype f32 --bandwidth 100000 fm --deviation 75000 | play -t raw -r 228000 -e floating-point -b32 -c 1 -V1 -

demodulate FSK9600 wav IQ data recording

Demodulate FSK9600 raw IQ data recording and pipe output to multimon-ng for packet decoding, notice --squarewave flag is added to FM demodulation, which makes demodulator output square like (multimon-ng likes it more)

sox -t wav sdr_fsk9600.wav -esigned-integer -b16  -r 126000 -t raw - | demod_fm --samplerate 126000 --resamplerate 48000 --bandwidth 4500 fm --deviation 3500 --squarewave | multimon-ng -t raw -a FSK9600 /dev/stdin

for testing AX25 decoding use this ax25_fsk9600_1024k_i16.wav with the following command (install doppler from here):

sox -t wav ax25_fsk9600_1024k_i16.wav -esigned-integer -b16  -r 126000 -t raw - | doppler const -s 126000 -i i16 --shift 14500 | demod_fm -s 126000 -r 48000 -i i16 -o i16 --bandwidth 4500 fm --deviation 3500 --squarewave | multimon-ng -t raw -a FSK9600 /dev/stdin

Notice that here modified multimon-ng is used that supports 48000 sps input stream for fsk9600 decoder. Read here why multimon-ng must be modified instead of converting demod output to native 22050 format.

decode RDS data

Decode RDS data easily by piping to redsea tool.

cat testfiles/fm_radio_rds_228000sps_u8.iq | demod_fm --samplerate 228000 --intype u8 --outtype i16 --bandwidth 100000 fm --deviation 75000 | redsea  -r 228000

test files

An IQ record of FM radio with RDS data has been generated from a Stereo MPX signal produced with PiFMRds and then modulated with the GNU Radio Frequency Mod block:

testfiles/fm_radio_rds_228000sps_f32.iq

The resulting IQ record has also been resampled from its original 32 bits float complex format to 8 bits signed integer complex, 8 bits unsigned integer complex and 16 bits signed integer complex:

testfiles/fm_radio_rds_228000sps_s8.iq
testfiles/fm_radio_rds_228000sps_u8.iq
testfiles/fm_radio_rds_228000sps_s16.iq