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77 lines
2.9 KiB
Markdown
77 lines
2.9 KiB
Markdown
# ACARSDEC
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Aircraft Communication Addressing and Reporting System (or ACARS) is a digital datalink system for transmission of small messages between aircraft and ground stations via VHF radio.
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Acarsdec is an open source, realtime ACARS demodulator and position decoder for Linux.
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## HOW DOES IT WORK ?
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To receive ACARS you need at least an AM VHF air band receiver tuned to one of these frequencies:
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- 131.725 Europe primary
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- 131.525 European secondary
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- 131.550 USA primary
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- 130.025 USA secondary
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- 131.450 Japan primary
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(These frequencies are the most common, Google is your friend for other frequencies)
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Audio output from this receiver is send to the soundcard input of your PC under Linux.
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Then, acarsdec will demodulate the signals sent by aircraft and print the received messages on its standard output in airnav log text format.
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## BUILDING IT
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On a Linux system, you will need libsnd library, alsa audio system and gcc/make installed.
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Then just type:
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`make`
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## USING IT
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acarsdec could be called with the following options:
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```
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acarsdec [-LR][-s noport] -d alsapcmdevice | -f sndfile
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-f sndfile : decode from file sndfile (ie: a .wav file)
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-d alsapcmdevice : decode from soundcard input alsapcmdevice (ie: hw:0,0)
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[-LR] : disable left or right channel decoding of stereo signal (save cpu)
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[-s noport ] : "xastir" mode : act as an APRS local server, on port : noport (see below)
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```
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Input could be mono or stereo but with 48Khz sampling frequency.
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If stereo, acarsdec will demod the 2 channels independently (if no L or R options specified)
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Typical usage for realtime decoding is :
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`acarsdec -d hw:0`
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Be sure that correct record level is set for the used soundcard input.
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For testing, you could try to record your receiver output at 48khz sampling frequency with any audio recording tool.
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Save as wav file, then decode it by:
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`acarsdec -f audiofile.wav`
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## USING IT WITH XASTIR
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acarsdec have a special output mode to use it with APRS position reporting plotting program: [xastir](www.xastir.org).
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In this mode, acarsdec acts as a very basic local aprsd server.
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ACARS messages, and in particular, position report messages are converted to APRS format, so you can plot aircraft positions on a map.
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PS: position decoding is in experimental stage. Mail me if you find errors or lack of position reporting.
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Start acarsdec with the following option:
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`acarsdec -d hw:0 -s 14000`
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Then in xastir, choose:
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- Interface → Interface Control → Add
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- Select: Internet Server, then Add
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- Set Host at 127.0.0.1, Port 14000, Don't allow transmitting, then OK.
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This will add an interface in the Interface Control dialog.
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Then select this interface and press start.
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To check that acarsdec send messages to xastir, select View→Incoming traffic
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ACARS messages look like that in xastir:
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```
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F-XXYZ>ACARS:>Fid:AFXXXX Lbl:Q0
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```
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Lots of ACARS messages are messages without position report, so be patient before seeing aircraft plotted on the map.
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