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Acarsdec is a multi-channels acars decoder with built-in rtl_sdr front end. Since 3.0, It comes with a database backend : acarsserv to store receved acars messages. (See acarsserv chapter below).

Features :

  • up to 8 channels decoded simultaneously
  • error detection AND correction
  • input via alsa sound card, rtl_sdr, or airspy software defined radios (SDR)
  • logging data over UDP in planeplotter or acarsserv formats to store in an sqlite database.

Multi-channel decoding is particularly useful with the RTL dongle. It allows the user to directly monitor 8 different frequencies simultaneously with very low cost hardware.


acarsdec [-v] [-o lv] [-t time] [-A] [-n|N ipaddr:port] [-i stationid] [-l logfile] -a alsapcmdevice | -r rtldevicenumber f1 [f2] [... fN] | -s f1 [f2] [... fN]

-v : verbose

-A : don't display uplink messages (ie : only aircraft messages)

-o lv : output format : 0: no log, 1 one line by msg., 2 full (default), 3 monitor mode

-t time : set forget time (TTL) in seconds in monitor mode(default=600s)

-l logfile : Append log messages to logfile (Default : stdout)

-n ipaddr:port : send acars messages to addr:port via UDP in planeplotter compatible format

-N ipaddr:port : send acars messages to addr:port via UDP in acarsdec format

-i station id: id use in acarsdec network format.

-a alsapcmdevice : decode from soundcard input alsapcmdevice (ie: hw:0,0)

-r rtldevice f1 [f2] ... [fN] : decode from rtl dongle number or S/N "rtldevice" receiving at VHF frequencies "f1" and optionally "f2" to "fN" in Mhz (ie : -r 0 131.525 131.725 131.825 ). Frequencies must be within the same 2MHz.

-g gain : set rtl preamp gain in tenth of db (ie -g 90 for +9db). By default use maximum gain

-p ppm : set rtl ppm frequency correction

-s f1 [f2] ... [fN] : decode from airspy receiving at VHF frequencies "f1" and optionally "f2" to "fN" in Mhz (ie : -s 131.525 131.725 131.825 ). Frequencies must be within the same 2MHz.


Decoding from sound card with short output :

acarsdec -o1 -a hw:0,0

Decoding from rtl dongle number 0 on 3 frequencies , sending aircraft messages only to on port 5555 and no other loging :

acarsdec -A -N -o0 -r 0 131.525 131.725 131.825

Decoding from airspy on 3 frequencies with verbose logging

acarsdec -s 131.525 131.725 131.825

Decoding from sound file test.wav (included) :

acarsdec -f test.wav

Output formats examples

One line by mesg format (-o 1)

#2 (L:  -5 E:0) 25/12/2016 16:26:40 .EC-JBA IB3166 X B9 J80A /EGLL.TI2/000EGLLAABB2
#3 (L:   8 E:0) 25/12/2016 16:26:44 .G-OZBF ZB494B 2 Q0 S12A 
#3 (L:   0 E:0) 25/12/2016 16:26:44 .F-HZDP XK773C 2 16 M38A LAT N 47.176/LON E  2.943

Full message format (-o 2)

[#1 (F:131.825 L:   4 E:0) 25/12/2016 16:27:45 --------------------------------
Aircraft reg: .A6-EDY Flight id: EK0205
Mode : 2 Label : SA Id : 4 Ack : !
Message no: S31A :

[#3 (F:131.825 L:   3 E:0) 25/12/2016 16:28:08 --------------------------------
Aircraft reg: .F-GSPZ Flight id: AF0940
Mode : 2 Label : B2 Id : 1 Ack : !
Message no: L07A :
/PIKCLYA.OC1/CLA 1627 161225 EGGX CLRNCE 606
46N020W 45N027W 44N030W 40N040W 36N050W
34N055W 32N060W 27N070W
FM ETIKI/1720 MNTN F340 M083

Monitoring mode (-o 3)

             Acarsdec monitor
 Aircraft Flight  Nb Channels   Last     First
 .CN-RNV  AT852X   9 .x.      16:25:58 16:21:05
 .F-HBMI  ZI0321   1 .x.      16:25:52 16:25:52
 .F-GSPZ  AF0940   6 ..x      16:25:21 16:22:30
 .D-ABUF  DE0252   1 .x.      16:25:20 16:25:20
 .EC-MGS  V72422   1 .x.      16:25:07 16:25:07
 .G-EUUU  BA733C   2 .x.      16:24:38 16:24:33


acarsdec must compile directly on any modern Linux distrib. It has been tested on x86_64 with fedora 19-25, Ubuntu 16, and on RaspberryPI (only RTL source tested)

It depends on some external libraries :

  • libasound for sound card input (rpm package alsa-lib-devel on fedora)
  • librtlsdr for software radio rtl dongle input (
  • libairspy for airspy software radio input

If you don't have or don't need one of these libs, edit CFLAGS and LDFLAGS in Makefile. Ie for rtl decoding only :

CFLAGS= -Ofast -D WITH_RTL -pthread LDLIBS= -lm -pthread -lrtlsdr

Notes :

  • change compiler options to suit your hardware, particularly on ARM platform -ffast-math -march -mfloat-abi -mtune -mfpu must be set correctly.
  • You could change the sample rate by changing RTLMULT in rtl.c. For rtl sdr default is 2.5Ms/s which is the best but could be over the limits of some hardware. Lowering sample rate will decrease CPU usage too.


acarsserv is a companion program for acarsdec. It listens to acars messages on UDP coming from one or more acarsdec processes and stores them in a sqlite database.

To compile it, just type :

make acarsserv

acarsserv need sqlite3 dev libraries (on Fedora : sqlite-devel rpm, on Ubuntu : libsqlite3-dev ).

By default, it listens to any addresses on port 5555. So running :

acarserv &

must be sufficient for most configs.

Then run (possibly on an other computer) :

acarsdec -A -N -o0 -r 0 131.525 131.725 131.825 (where is the ip address of your computer running acarsserv).

acarsserv will create by default an acarsserv.sqb database file where it will store received messages. You could read its content with sqlite3 command (or more sophisticated graphical interfaces).

acarsserv has some messages filtering and network options (UTSL).


ACARS SDR decoder



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