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.

Based on acarsdec 2.1 Copyright (c) 2014 Thierry Leconte. See http://sourceforge.net/projects/acarsdec/.

UDP output to PlanePlotter added by Neil Greatorex (https://github.com/ngreatorex/acarsdec/).

 acarsdec [-v] [-o lv] [-u host port] [-A] [-g gain] [-p ppm] -a alsapcmdevice  | -f sndfile | -r rtldevicenumber  f1 [f2] [f3] [f4]

 -v :                   verbose
 -o lv :                output format : 0 one line by msg., 1 full (default), 2 UDP to PlanePlotter
 -u host port : specify the PlanePlotter host and port to send UDP messages to
 -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 )

For any input source , up to 4 channels  could be simultanously decoded

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

Decoding from multichannel wav file and sending output to PlanePlotter on host called pc1: acarsdec -o 2 -u pc1 9742 -f test.wav

Decoding from calibrated (+80ppm) rtl dongle on 131.725Mhz and 131.825 and sending output to PlanePlotter on host called pc1: acarsdec -o 2 -u pc1 9742 -p 80 -r 0 131.725 131.825

acarsdec will compile directly on any modern Intel Linux distrib.

This version has been modified to compile on Raspberry Pi and any other processor.

If you want to compile it on a processor that supports SSE2, #define USE_SSE2 in acarsdec.h and add back -msse2 to the CFLAGS in the Makefile

It depends on 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.

To compile on a Raspberry Pi (this assumes you have already compiled and installed RTL-SDR):

$ sudo apt-get libsndfile-dev libasound-dev
$ make

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  

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