Acarsdec is a multi-channels acars decoder with built-in rtl_sdr front end.

The 2.x version is a complete rewrite, very few code line remains from 1.x

Features :

• new and improved msk demodulator
• up to four channels decoded simultaneously
• multithreaded, sse2 optimized
• error detection AND correction (correct all one error and some two errors)
• input from sound file (.wav) , alsa sound card or software defined radio (SRD) via a rtl dongle (http://sdr.osmocom.org/trac/wiki/rtl-sdr)

The 4 channels decoding is particularly useful with the rtl dongle. It allows to directly listen simultaneously to 4 different frequencies , with a very low cost hardware.

Usage : acarsdec [-v] [-o lv] [-g gain] [-A] -a alsapcmdevice | -f sndfile | -r rtldevicenumber f1 [f2] [f3] [f4]

-v : verbose -o lv : output format : 0 one line by msg., 1 full (default) -A : don't display uplink messages (ie : only aircraft messages) -g gain : set rtl preamp gain in tenth of db. By default use AGC (ie -g 90 for +9db) -p ppm : set rtl ppm frequency correction -f sndfile : decode from sound file (ie: a .wav file) -a alsapcmdevice : decode from soundcard input alsapcmdevice (ie: hw:0,0) -r rtldevicenumber f1 [f2] [f3] [f4] : decode from rtl dongle number rtldevicenumber receiving at VHF frequencies f1 and optionaly f2 to f4 in Mhz (ie : -r 0 131.525 131.725 131.825 )

Examples :

Decoding from multichannel wav file : acarsdec -v -f test.wav

Decoding from sound card with short output : acarsdec -o 0 -a hw:0,0

Decoding donwlink messages from rtl dongle number 0 on 3 frequencies : acarsdec -A -r 0 131.525 131.725 131.825

Compilation : acarsdec must compile directly on any modern Intel Linux distrib. It has been tested on x86_64 with fedora 19. If you want to compile it on an other processor, undefine USE_SSE2 in acarsdec.h

It depends of 3 external libraries :

• libsndfile for sound file input (rpm package libsndfile-devel on fedora)
• libasound for sound card input (rpm package alsa-lib-devel on fedora)
• librtlsdr for software radio rtl dongle input (http://sdr.osmocom.org/trac/wiki/rtl-sdr)

If you don't have or don't need one of these libs, edit the #define at the beginning of acarsdec.h, to opt-out corresponding code and edit the LDLIBS setting in Makefile.

Testing : acarsdec-2.x.tar include a test.wav file. It's a 4 channels audio file that contains 7 acars messages.

./acarsdec -o 0 -f test.wav #2 .PH-BXR KL1681 5V S53A
#4 .LN-DYY DY083J Q0 S46A
#2 .LN-DYY DY083J Q0 S47A
#1 .F-GTAE AF7728 H1 D65C #DFB00000/V206,05,124,183,02,00,0 #1 .LN-DYY _d
#3 .G-DBCK BA031T _d S64A
#3 .G-DBCK BA031T Q0 S63A

Notes : Include sse2 vectorized math functions by Julien Pommier (see sse_mathfun.h)