What is ACARS?

ACARS is an acronym for Aircraft Communications Addressing and Reporting System which is a digital communications system that aircraft use to send and receive short messages to and from ground stations.

Standard ACARS transmits at a frequency of 131.550MHz, which is squarely in the receivable range of the RTL-SDR. The RTL-SDR software radio can be used as a radio scanner for listening to these digital messages, and with the help of some decoding software, can be used to decode and display the messages. The messages you can receive will be from nearby aircraft and ground stations. Most messages will be unreadable data intended for computers, but you can find out what is flying near you by decoding the flight number and aircraft registration details sent with every message.

There is also HF ACARS, which is used for long distance communications. In this article the focus will be on VHF ACARS, as receiving HF ACARS is a little different.

Examples of RTL-SDR used to decode ACARS

YouTube user Superphish shows a timelapse over 5 hours of ACARS traffic and decoding using SDR# and decoding program acarsd. He used a J-Pole antenna.

YouTube user moonfestmadness shows another RTL-SDR video also with SDR# and decoding program acarsd. You can also hear what ACARS sounds like in this video.

In this video, hamradioscience uses multiple RTL-SDR dongles to add ADS-B and ACARS decoding to PlanePlotter.

Tutorial – Decoding ACARS using SDRSharp and RTL-SDR

We will assume you have bought and set up RTL-SDR with SDRSharp. If you have not bought an RTL-SDR yet, see the buy RTL-SDR page and then the quickstart guide.

You will also need to have an audio piping method set up. Either first set up windows stereo mix, or download and install virtual audio cable (paid with trial) or the free VB-Cable. Ensure the audio method you use in SDRSharp is set to the default audio device in the windows recording audio settings.

If you are unfamiliar with ACARS signals, an example of the waterfall produced by ACARS signals is shown on the left. An audio example is also provided below.

Now to decode ACARS follow these steps.

1. Open SDRSharp, and set the output audio device to the audio piping method you intend to use.
2. Tune to an ACARS frequency. Use a bandwidth of around 5-10 kHz, 6 kHz works best for me. The main ACARS frequency is at 131.550 Mhz.
3. Adjust the RTL-SDR tuner gain under the SDRSharp configure button for best reception.
4. Set the receive mode to AM. For now turn OFF the squelcher and turn OFF Filter Audio. You may experiment later with the squelcher on and with audio AGC if you’d like.

Note, if you are experienced with SDR-RADIO, you may want to use it instead of SDR#. With SDR-RADIO you can output multiple ACARS frequency channels to the same audio device instead of just one. This will increase the number of decoded messages you get.

There are many software packages that can be used to decode the received ACARS packets. PlanePlotter is one good decoding program. It has a trial period of 21 days after which you must purchase a licence for 25 euros. Acarsd is a free decoding program, however we find its decoding performance to be inferior when compared to PlanePlotter, but some other users have reported the exact opposite so it may or may not work for you. AirNav ACARS is another paid decoding program, but is a little pricer than PlanePlotter.

Using PlanePlotter to Decode ACARS

Go to the PlanePlotter website, scroll down and download and install the latest PlanePlotter version.

1. Open PlanePlotter. Click on the “I/O Settings” icon that looks like a spanner with an ‘i’ to its left. You can see the icon name by hovering over it with your mouse.
2. Ensure that the option “ACARS reception from audio input is checked”. Push OK.

3. Go to Options->Audio->ACARS->Source. Ensure that the audio source SDRSharp is outputting to is selected.
4. Press the “Start” button which is the green circle icon. This will start the decoding.
5. Press the “Signal” icon which is the icon to the right of the start button. This shows a graph of signal volume. Ensure the signal is not too loud. This image shows an appropriate volume level for the static in between data packets. You will know the volume is too loud if the graph begins clipping/saturating (signal will look squarish) when ACARS packets are received.

6. Now you can look at either the “Message View” or “Aircraft View” which are the two icons next to the Signal icon to see the decoded information.
7. Right clicking on an entry in the Aircraft View tab will bring up an internet browser with information about that particular aircraft.

Using ACARSD to Decode ACARS

ACARSD is a free ACARS decoding program. Personally, I find that it decodes less ACARS messages compared to the paid options, but other users have reported the exact opposite, so it is best if you try it out for yourself. If you would still like to try this software as it is free, follow the instructions below.

Go to the acarsd website and download and install acarsd. Make sure to follow the instructions on the website for installing.

1. Ensure your default audio device is set correctly in windows sound recording properties. Acarsd will use the first default audio device found. You may need to set your sound card to use 44100 Hz sampling and check this setting in the acarsd set up as well.
2. Run acarsd.exe in your acarsd folder to open acarsd.
3. Adjust the volume in SDRSharp or Windows so that the volume reading in the bottom right corner of the acarsd window is at around 0-10 for static. If the volume is too loud, acarsd will not decode the ACARS message.
4. Decoded ACARS packets should begin to show up.

The number of decoder passes can be changed in Windows->acarsdgui settings. Setting it higher may improve decode performance.

If you need a free ACARS decoder, you may be able to try rtl_acars or acarsed for Linux, but these are harder to set up.

Some ACARS Tips

• You will need a decent outside antenna to get good signal strength. A discone, j-pole or colinear antenna placed up high and tuned to the airband frequencies may be good options to research.
• ACARS packets usually do not contain location information. If you are interested in tracking aircraft like a radar using RTL-SDR, see ADSB decoding.
• Most of the actual ACARS messages will be displayed as gibberish. These messages are intended for the on board avionics computers and ground telemetry.
• Note that receiving ACARS in some countries may be illegal. Please decode responsibly.
• Once you get the hang of ACARS with SDRSharp, you may want to switch to SDR-RADIO. The reason that SDR-RADIO may be better is that it is possible to listen to up to six ACARS channels simultaneously with multiple VFOs. Just send the VFO audio to the same audio output device.

ACARS Frequencies

Most ACARS packets will be on the primary 131.550MHz frequency. But around the world, various other frequencies are also used.

Table Source: Acarsd

Other Decoding Software

General purpose ham software like MultiPSK and pager decoding software PDW can also decode ACARS packets. However, these generally do not link to an aircraft spotting website.

There are also the Linux based command line based programs such as rtl_acars and acarsed. Acarsed

If you enjoyed this tutorial you may like our ebook available on Amazon. The Hobbyist’s Guide to the RTL-SDR: Really Cheap Software Defined radio.

The post RTL-SDR Tutorial: Receiving Airplane Data with ACARS appeared first on rtl-sdr.com.

On the Osmocom mailing list, Andreas has posted his work on a console based ACARS decoder for the RTL-SDR. Check out the mailing list thread here, and original post here. The second post on the thread shows how to compile it under Linux. Andreas writes

I have combined “rtl_fm” with Thierry Leconte’s (GPL’ed) acarsdec library code and created “rtl_acars” which can directly decode ACARS flight info messages to the console. Confirmed to compile on OSX 10.6 (not possible for me to check if it also compiles under Windows and *nix). Feel free to add it as another proof of concept to your distro unless you consider it too much of a quick&dirty hack.

Only the source code is available, and you will need to compile it yourself. The code can be found here.

The post RTL_ACARS Console Acars Decoder for RTL-SDR appeared first on rtl-sdr.com.

Yesterday we posted about the command line rtl_acars ACARS decoder. Today on YouTube, Pawel Janowski has posted a video showing how to download, compile and run the rtl_acars.c code on Linux.

Pawel has also posted the compilation instructions on his blog (in Polish but the console commands are easy to discern from the text).

The post rtl_acars.c Compilation Install Video appeared first on rtl-sdr.com.

The rtl_acars console based ACARS decoder which is based on rtl_fm has been updated by a new author, gat3way on Reddit. The new updates include decoder sensitivity improvements and the following:

• Multiple frequencies scanning is now supported (by providing multiple -f arguments at command line and -l <squelch>). Since there is no audio output and it’s hard to determine right squelch level, a squelch debug option (-r) is implemented. Use it to experiment with squelch value, it’s simple: good squelch values flood stdout with “hopping freq!” messages yet avoid too high squelch levels. In general, values between 20-30 work good with my setup (big city, lots of radio interference, NOAA turnstile which gives -3db due to rhcp polarization).

• Aircraft and airline databases now supported (using the acarsdec builtin ones). DBs are text files using simple format, so you may easily update them. I would very much appreciate your help to keep that up-to-date.

• Certain improvements in frequency hopping code as compared to rtl_fm, but don’t expect wonders, it takes time to retune so data loss is not avoidable especially if you provide lots of frequencies to scan or huge ranges.
• A simple Makefile to make it simpler

In the future gat3way hopes to support the decoding of multiple ACARS channels as well. The updated rtl_acars software can be downloaded from github here.

The post RTL_ACARS Updated appeared first on rtl-sdr.com.

Acarsdec is a recently released open source, multi-channel realtime ACARS decoder for Linux. It supports direct input from an RTL-SDR dongle, and with the RTL-SDR can listen to four ACARS channels simultaneously. It’s official feature list includes

- up to four channels decoded simultaneously
– multithreaded
– error detection AND correction
– input from sound file , also sound card or software defined radio (SDR) via a rtl dongle

The post Acarsdec 2.0: A Multi-Channel Realtime Linux ACARS Decoder which supports RTL-SDR appeared first on rtl-sdr.com.

Over on YouTube user k2nccvids has posted two videos showing how he was able to decode High Frequency Data Link (HFDL) packets using the RTL-SDR, Ham-it-up upconverter, MultiPSK and HFDL Display. HFDL is a service similar to ACARS but sent over HF frequencies. It is used to sent short messages to and from aircraft and ground stations.

In the first video k2nccvids uses MultiPSK with the RTL-SDR directly and also uses the add on software HFDL Display to more clearly view received HFDL packets. In the second video he uses SDR-CONSOLEv2 to monitor three HFDL frequencies simultaneously, with MultiPSK and HFDL Display still being used for decoding and display.

The post Aircraft Messages with HFDL, MultiPSK and the RTL-SDR appeared first on rtl-sdr.com.

Back in August of this year we showed how it was possible to use an RTL-SDR dongle, satellite antenna, LNA and decoding software to receive and decode STD-C EGC signals from Inmarsat satellites. We also showed how it was possible to modify a low cost GPS antenna to use as a satellite antenna.

Now a radio hobbyist called Jonti has released a Windows decoder for the Inmarsat AERO set of signals. AERO is a system that provides a satellite based version of VHF ACARS (Aircraft Communications Addressing and Reporting System). ACARS is typically used by ground control and pilots to send short messages and is also sometimes used for telemetry.

Jonti writes:

JAERO is a program that demodulates and decodes Classic Aero ACARS (Aircraft Communications Addressing and Reporting System) messages sent from satellites to Aeroplanes (SatCom ACARS) commonly used when Aeroplanes are beyond VHF range. Demodulation is performed using the soundcard. Such signals are typically around 1.5Ghz and can be received with a simple low gain antenna that can be home brewed in a few hours in conjunction with a cheap RTL-SDR dongle.

In the advent of MH370, Classic Aero has become a well-known name. A quick search on the net using “Classic Aero MH370” will produce thousands of results. The Classic Aero signals sent from satellites to the Aeroplanes are what JAERO demodulates and decodes.

Unlike the usual VHF ACARS, with SatCom ACARS you can not receive signals from the Aeroplane only the people on the ground talking to the people in the Aeroplane. This means you do not get the airplanes reporting their position. Instead you tend to get weather reports, flight plans, and that sort of stuff. Just like VHF ACARS they usually use cryptic shorthand notation. For example “METAR YSSY 040400Z 08012KT 9999 FEW040 SCT048 23/09 Q1024 FM0500 05012KT CAVOK=” is the weather report for Sydney Airport in Australia in a format called METAR. It tells you the time, when the report was issued, the wind direction and speed, visibility, clouds, temperature, due point and air pressure. Then it says from 5 AM UTC the wind direction and speed and that the weather will be nice. There are sites such as Flight Utilities that can decode such information and display it in a more understandable format.

In his post Jonti also shows how he uses a modified GPS antenna to receive the AERO signals.

We gave JAERO a test and found that it decoded AERO signals easily, even with low signal strength. To use JAERO tune to an Inmarsat AERO signal in SDR# or a similar program using USB mode. JAERO will listen to the audio from the sound card or from a virtual audio pipe. We recommend setting the AFC (Automatic Frequency Control) setting on on if you find that your RTL-SDR drifts too much. 

AERO signals can be found at around 1545 MHz. They only use about 800 Hz in bandwidth. See UHF satcoms page for a list of AERO frequencies.

Remember that some R820T/2 RTL-SDR dongles can have problems when receiving this high, especially when they heat up. If you find that your dongle gets deaf at these L-band frequencies try cooling the R820T/2 chip with a heatsink or fan. The Airspy or SDRplay RSP software defined radios are better choices for decoding signals this high, but the RTL-SDR will work fine if your signal strength is decent and the R820T/2 chip is kept cool.

If you are interested in VHF ACARS as well, then we have a tutorial about decoding that here.

The post JAERO: A new RTL-SDR compatible decoder for Inmarsat AERO signals appeared first on rtl-sdr.com.

The JAERO decoder for AERO signals on Inmarsat satellites has recently been updated to version 1.03. This new version supports the decoding of 10.5k Aero-H and Aero-H+ signals. The author of JAERO Jonti writes that on these channels he’s seeing significantly more traffic than on the narrowband signals and that he was suprised to see that other non-aircraft messages such news was broadcast on this 10.5k signal. Jonti writes about his experience in developing the 10.5k decoder and his experience with receiving the messages in this post.

AERO is a system similar to VHF ACARS, but instead of running over terrestrial VHF it uses an L-band Inmarsat satellite link. Our first post about the JAERO decoder explains a bit about AERO, and this previous tutorial about decoding Inmarsat EGC messages may help you get set up with decoding Inmarsat signals in general.

If you like Jonti’s apps, then please remember to donate a small amount to him so that he can continue to work on them more. His PayPal donate button can be at the bottom of his main page.

The post JAERO Updated: Now supports 10.5k Aero-H and Aero-H+ appeared first on rtl-sdr.com.

JAERO is a program by Jonti that was released late last year which allows us to use a SDR such as an RTL-SDR to receive L-band and C-Band AERO messages. AERO is essentially the satellite based version of ACARS, and the L-band signals contains short ground to air messages with things like weather reports and flight plans intended to be transmitted to aircraft. The C-band signals are the air to ground portion of AERO and more difficult to receive as they require an LNB and large dish. However they are much more interesting as they contain flight position data, like ADS-B.

Over March JAERO has had some minor updates. It is now possible to display planes on a map by using it’s SBS1 protocol output and outputting the data to Virtual Radar Server. The second more recent update now allows JAERO to simultaneously monitor up to two C-band AERO channels. To do this you will need to use the AUX VFO plugin for SDR#.

If you enjoy JAERO, please remember consider donating to Jonti.

The post Recent Updates to the JAERO L-Band and C-Band AERO Decoder appeared first on rtl-sdr.com.

On the Osmocom mailing list, Andreas has posted his work on a console based ACARS decoder for the RTL-SDR. Check out the mailing list thread here, and original post here. The second post on the thread shows how to compile it under Linux. Andreas writes

I have combined “rtl_fm” with Thierry Leconte’s (GPL’ed) acarsdec library code and created “rtl_acars” which can directly decode ACARS flight info messages to the console. Confirmed to compile on OSX 10.6 (not possible for me to check if it also compiles under Windows and *nix). Feel free to add it as another proof of concept to your distro unless you consider it too much of a quick&dirty hack.

Only the source code is available, and you will need to compile it yourself. The code can be found here.

Yesterday we posted about the command line rtl_acars ACARS decoder. Today on YouTube, Pawel Janowski has posted a video showing how to download, compile and run the rtl_acars.c code on Linux.

Pawel has also posted the compilation instructions on his blog (in Polish but the console commands are easy to discern from the text).

The rtl_acars console based ACARS decoder which is based on rtl_fm has been updated by a new author, gat3way on Reddit. The new updates include decoder sensitivity improvements and the following:

• Multiple frequencies scanning is now supported (by providing multiple -f arguments at command line and -l ). Since there is no audio output and it’s hard to determine right squelch level, a squelch debug option (-r) is implemented. Use it to experiment with squelch value, it’s simple: good squelch values flood stdout with “hopping freq!” messages yet avoid too high squelch levels. In general, values between 20-30 work good with my setup (big city, lots of radio interference, NOAA turnstile which gives -3db due to rhcp polarization).

• Aircraft and airline databases now supported (using the acarsdec builtin ones). DBs are text files using simple format, so you may easily update them. I would very much appreciate your help to keep that up-to-date.

• Certain improvements in frequency hopping code as compared to rtl_fm, but don’t expect wonders, it takes time to retune so data loss is not avoidable especially if you provide lots of frequencies to scan or huge ranges.
• A simple Makefile to make it simpler

In the future gat3way hopes to support the decoding of multiple ACARS channels as well. The updated rtl_acars software can be downloaded from github here.

Acarsdec is a recently released open source, multi-channel realtime ACARS decoder for Linux. It supports direct input from an RTL-SDR dongle, and with the RTL-SDR can listen to four ACARS channels simultaneously. It’s official feature list includes

– up to four channels decoded simultaneously
– multithreaded
– error detection AND correction
– input from sound file , also sound card or software defined radio (SDR) via a rtl dongle

Over on YouTube user k2nccvids has posted two videos showing how he was able to decode High Frequency Data Link (HFDL) packets using the RTL-SDR, Ham-it-up upconverter, MultiPSK and HFDL Display. HFDL is a service similar to ACARS but sent over HF frequencies. It is used to sent short messages to and from aircraft and ground stations.

In the first video k2nccvids uses MultiPSK with the RTL-SDR directly and also uses the add on software HFDL Display to more clearly view received HFDL packets. In the second video he uses SDR-CONSOLEv2 to monitor three HFDL frequencies simultaneously, with MultiPSK and HFDL Display still being used for decoding and display.

Back in August of this year we showed how it was possible to use an RTL-SDR dongle, satellite antenna, LNA and decoding software to receive and decode STD-C EGC signals from Inmarsat satellites. We also showed how it was possible to modify a low cost GPS antenna to use as a satellite antenna.

Now a radio hobbyist called Jonti has released a Windows decoder for the Inmarsat AERO set of signals. AERO is a system that provides a satellite based version of VHF ACARS (Aircraft Communications Addressing and Reporting System). ACARS is typically used by ground control and pilots to send short messages and is also sometimes used for telemetry.

Jonti writes:

JAERO is a program that demodulates and decodes Classic Aero ACARS (Aircraft Communications Addressing and Reporting System) messages sent from satellites to Aeroplanes (SatCom ACARS) commonly used when Aeroplanes are beyond VHF range. Demodulation is performed using the soundcard. Such signals are typically around 1.5Ghz and can be received with a simple low gain antenna that can be home brewed in a few hours in conjunction with a cheap RTL-SDR dongle.

In the advent of MH370, Classic Aero has become a well-known name. A quick search on the net using “Classic Aero MH370” will produce thousands of results. The Classic Aero signals sent from satellites to the Aeroplanes are what JAERO demodulates and decodes.

Unlike the usual VHF ACARS, with SatCom ACARS you can not receive signals from the Aeroplane only the people on the ground talking to the people in the Aeroplane. This means you do not get the airplanes reporting their position. Instead you tend to get weather reports, flight plans, and that sort of stuff. Just like VHF ACARS they usually use cryptic shorthand notation. For example “METAR YSSY 040400Z 08012KT 9999 FEW040 SCT048 23/09 Q1024 FM0500 05012KT CAVOK=” is the weather report for Sydney Airport in Australia in a format called METAR. It tells you the time, when the report was issued, the wind direction and speed, visibility, clouds, temperature, due point and air pressure. Then it says from 5 AM UTC the wind direction and speed and that the weather will be nice. There are sites such as Flight Utilities that can decode such information and display it in a more understandable format.

In his post Jonti also shows how he uses a modified GPS antenna to receive the AERO signals.

We gave JAERO a test and found that it decoded AERO signals easily, even with low signal strength. To use JAERO tune to an Inmarsat AERO signal in SDR# or a similar program using USB mode. JAERO will listen to the audio from the sound card or from a virtual audio pipe. We recommend setting the AFC (Automatic Frequency Control) setting on on if you find that your RTL-SDR drifts too much. 

AERO signals can be found at around 1545 MHz. They only use about 800 Hz in bandwidth. See UHF satcoms page for a list of AERO frequencies.

Remember that some R820T/2 RTL-SDR dongles can have problems when receiving this high, especially when they heat up. If you find that your dongle gets deaf at these L-band frequencies try cooling the R820T/2 chip with a heatsink or fan. The Airspy or SDRplay RSP software defined radios are better choices for decoding signals this high, but the RTL-SDR will work fine if your signal strength is decent and the R820T/2 chip is kept cool.

If you are interested in VHF ACARS as well, then we have a tutorial about decoding that here.

The JAERO decoder for AERO signals on Inmarsat satellites has recently been updated to version 1.03. This new version supports the decoding of 10.5k Aero-H and Aero-H+ signals. The author of JAERO Jonti writes that on these channels he’s seeing significantly more traffic than on the narrowband signals and that he was suprised to see that other non-aircraft messages such news was broadcast on this 10.5k signal. Jonti writes about his experience in developing the 10.5k decoder and his experience with receiving the messages in this post.

AERO is a system similar to VHF ACARS, but instead of running over terrestrial VHF it uses an L-band Inmarsat satellite link. Our first post about the JAERO decoder explains a bit about AERO, and this previous tutorial about decoding Inmarsat EGC messages may help you get set up with decoding Inmarsat signals in general.

If you like Jonti’s apps, then please remember to donate a small amount to him so that he can continue to work on them more. His PayPal donate button can be at the bottom of his main page.

JAERO is a program by Jonti that was released late last year which allows us to use a SDR such as an RTL-SDR to receive L-band and C-Band AERO messages. AERO is essentially the satellite based version of ACARS, and the L-band signals contains short ground to air messages with things like weather reports and flight plans intended to be transmitted to aircraft. The C-band signals are the air to ground portion of AERO and more difficult to receive as they require an LNB and large dish. However they are much more interesting as they contain flight position data, like ADS-B.

Over March JAERO has had some minor updates. It is now possible to display planes on a map by using it’s SBS1 protocol output and outputting the data to Virtual Radar Server. The second more recent update now allows JAERO to simultaneously monitor up to two C-band AERO channels. To do this you will need to use the AUX VFO plugin for SDR#.

If you enjoy JAERO, please remember consider donating to Jonti.

On the Osmocom mailing list, Andreas has posted his work on a console based ACARS decoder for the RTL-SDR. Check out the mailing list thread here, and original post here. The second post on the thread shows how to compile it under Linux. Andreas writes

I have combined “rtl_fm” with Thierry Leconte’s (GPL’ed) acarsdec library code and created “rtl_acars” which can directly decode ACARS flight info messages to the console. Confirmed to compile on OSX 10.6 (not possible for me to check if it also compiles under Windows and *nix). Feel free to add it as another proof of concept to your distro unless you consider it too much of a quick&dirty hack.

Only the source code is available, and you will need to compile it yourself. The code can be found here.

Yesterday we posted about the command line rtl_acars ACARS decoder. Today on YouTube, Pawel Janowski has posted a video showing how to download, compile and run the rtl_acars.c code on Linux.

Pawel has also posted the compilation instructions on his blog (in Polish but the console commands are easy to discern from the text).

The rtl_acars console based ACARS decoder which is based on rtl_fm has been updated by a new author, gat3way on Reddit. The new updates include decoder sensitivity improvements and the following:

• Multiple frequencies scanning is now supported (by providing multiple -f arguments at command line and -l ). Since there is no audio output and it’s hard to determine right squelch level, a squelch debug option (-r) is implemented. Use it to experiment with squelch value, it’s simple: good squelch values flood stdout with “hopping freq!” messages yet avoid too high squelch levels. In general, values between 20-30 work good with my setup (big city, lots of radio interference, NOAA turnstile which gives -3db due to rhcp polarization).

• Aircraft and airline databases now supported (using the acarsdec builtin ones). DBs are text files using simple format, so you may easily update them. I would very much appreciate your help to keep that up-to-date.

• Certain improvements in frequency hopping code as compared to rtl_fm, but don’t expect wonders, it takes time to retune so data loss is not avoidable especially if you provide lots of frequencies to scan or huge ranges.
• A simple Makefile to make it simpler 🙂

In the future gat3way hopes to support the decoding of multiple ACARS channels as well. The updated rtl_acars software can be downloaded from github here.