After the fantastic feedback i got for my blog post about ADSB reception with RTL-SDR (and Docker), the next point in my list is ACARS.

The basics: What is ACARS?

ACARS is short for Aircraft Communications Addressing and Reporting System, a digital data link between an aircraft and a ground station and/or satellite.

The on-board avionic computer system (aircraft) consists of the ACARS Management Unit (ACARS MU) and a Control Display Unit (CDU) for sending and receiving digital information messages from the ground-based stations.

Ground equipment is made up of a network of radio transceivers managed by a central site computer called AFEPS (Arinc Front End Processor System), which handles and routes messages. Generally, ground ACARS units are either government agencies such as the Federal Aviation Administration, an airline operations headquarters, or, for small airlines or general aviation, a third-party subscription service. Usually government agencies are responsible for clearances, while airline operations handle gate assignments, maintenance, and passenger needs. _(Wikipedia)

This is a message send by the CFD (Central Fault Display) of an aircraft 😉

#CFB.1/WRN/WN1511161031 383100506MAINTENANCE STATUS TOILET

Or something like this

N12114 CO0070 1EHAM REQUEST GATE ASSIGNMENT ETA0447

You’re now interested how to receive such messages with minimal Hardware? You have your Raspberry Pi 2 ready? Docker installed? RTL-SDR attached? Then read on.

If not, start with my earlier blog posts to get the basics:

• Docker on a Raspberry Pi
• Raspberry Pi + Docker + RTL-SDR

Choose your weapon

For my ACARS experiments, I’ll go with acarsdec, a Linux console tool which plays nicely with the RTL-SDR gear.

Features:

•  up to four channels decoded simultaneously
• error detection AND correction
• input from sound file , alsa sound card or software defined radio (SRD) via a rtl dongle or airspy
• could send decoded acars to a server via UDP in Planeplotter format or its own dedicated format

Dockerize it

Hint: If you want to skip the next manual steps, just clone my Bitbucket repo fgranna/rpi-acarsdec/3.2 and proceed to the step Build & Run

Ok, first we nee a fresh and clean new directory for our files. Just create one called acarsdec.

Next we have to download the acarsdec sourcecode. Head over to this page and click the latest version (currently 3.2). You can now download the compressend source (acarsdec-3.2.tar.gz). Put this file into your acarsdec folder.

Now extract this file – we need the Makefile for the next step. Copy the Makefile to your acarsdec folder – the other extracted files are not needed anymore, just remove them – but keep the compressed source file (acarsdec-3.2.tar.gz)!

You should now have 2 files in your acarsdec folder: the Makefile and the source zip. All good? Ok, now we have to modify the Makefile to be able to build the acarsdec programm for our Raspberry Pi. Open the Makefile and change the first lines like this:

Just remove all the other lines beginning with #CFLAGS, CFLAGS, #LDLIBS or LDLIBS.

 Well done (i hope). Next step is the Dockerfile to build our Image. Create a new file called Dockerfile in your acarsdec folder and add the following content:

That should be all 🙂 Now proceed and build the image

Build & Run

Lets build the docker image. Just got to your acarsdec folder (yes, the ,one with the three files in it) and run

docker build --rm -t acarsdec .

Docker will now download my rtl-sdr baseimage for Raspberry Pi, compile acarsdec and build the image. Easy, is’nt it?

After the image is build, you can do a dry-run:  docker run -it --rm acarsdec  – this should output the help information of the tool:

Looks good? Cool, then let’s try a real test-run 🙂

docker run -it --rm --device=/dev/bus/usb acarsdec -v -g 450 -r 0 131.450 131.550

Let me explain this command a bit. –device=/dev/bus/usb gives the Container access to our usb devices (rtl-sdr stick), -g 450 sets the tuner gain to ~45db, the parameter -r 0 <freq1> <freq2> sets the 2 ACARS frequencies for Australia and enables them on stick nr 0 (our first stick – yes you could use multiple). Depeding on the country your sitting, you should check other frequencies (i added a short overview at the bottom of this post)

Now you should get the first ACARS messages  🙂

If something is not clear or not working, just drop me a line in the comments or via Twitter

Current ACARS Frequencies