Episode 4 · ACARS and VDL2 · Series 01: The Listening Station
What do aircraft say, not only where they are?
Coming soon- Release
- Length
- 3:39
- On the dial
- 131 and 136 MHz
- Signal
- ACARS
What it covers
ADS-B tells me where an aircraft is. ACARS tells me what it says: short text messages with times, positions, weather requests and fault codes. In this video I explain ACARS and its faster successor, VDL Mode 2, and how one antenna, two USB radios and open software decode thousands of these messages a day.
Chapters
- 0:00Intro
- 0:25The messages
- 1:00Two systems
- 1:27One antenna, two radios
- 1:58Two decoders
- 2:28The message
- 2:52My station
Frames from the draft
Gear in this episode
| Diamond D-130J discone antenna | the wide-band antenna on my roof (25 to 1300 MHz) |
| RTL-SDR Blog FM band-stop filter | the filter that blocks FM broadcast stations on my wide antenna |
| Mini-Circuits ZX10-2-12-S+ splitter | feeds two radios from one antenna (mine came from a surplus dealer) |
| Airspy R2 | the USB radio I use for ACARS |
| RTL-SDR Blog V4L | the USB radio I use for VDL Mode 2 |
| Awxlumv aluminum heat sinks, 50 x 25 x 10 mm (2 pack) | the heat sinks I add to most of my SDR dongles (not part of the radios as sold) |
| Raspberry Pi 5 | the small computer that runs the decoder |
| Rosonway RSH-A10 powered USB hub | feeds power and data to the radios on Donatello |
| SO-239 to SMA adapter | joins the discone cable to the SMA parts |
| Short SMA jumper cables | connect filter, splitter and radios |
| CyberPower CP1500PFCLCD UPS (1500 VA, sine wave) | the battery backup that keeps almost all of my station running through a power cut |
Software and references
| acarsdecgithub.com | the ACARS decoder (the version in the container below) |
| dumpvdl2github.com | the VDL Mode 2 decoder |
| acars_routergithub.com | removes duplicates and sends the messages on |
| ACARS Hub (docker-acarshub)github.com | the message screen on my home network |
| docker-acarsdecgithub.com | acarsdec packaged as a container |
| docker-dumpvdl2github.com | dumpvdl2 packaged as a container |
| airframes.ioairframes.io | the community network that collects aircraft messages |
What is simplified, and what is invented
- The example message is invented: the aircraft, the flight and the time do not exist. Only the layout is real. I never show a received message, because real messages can contain private details.
- The example message is simplified: the mode, acknowledgement and checksum characters are left out.
- The flight drawing is not to scale. The channel cells in the decoder drawing are not to scale, and the flashes in them are an illustration.
- The amplifier numbers come from one test on one day, made before the splitter was installed.
- The message shares and the ratio are all-time counts from my station, rounded. Other places have other busy channels.
- The speeds on screen are the raw bit rates of the two radio links.