VDLM2DEC

vdlm2dec is a vdl mode 2 decoder with built-in rtl_sdr or airspy front end.

It could decode up to 8 frequencies simultaneously ( but in the same 2Mhz range )

Usage

vdlm2dec [-l logfile] [-g gain] [-r rtldevicenumber] Frequencies(Mhz)

-r rtldevicenumber : decode from rtl dongle number rtldevicenumber (don't set it for airspy)

-g gain : set preamp gain in tenth of db (ie -g 90 for +9db)

-p ppm : set rtl sdr ppm frequency (rtl_sdr only)

-q : quiet

-l logfile : output log (stderr by default)

-J : json output

-j addr:port send to addr:port UDP packets in json that could be read by acarsserv

Examples

For rtl-sdr :

./vdlm2dec -r 0 136.725 136.775 136.875 136.975

For airspy :

./vdlm2dec 136.725 136.775 136.875 136.975

[#4 (F:136.975 P:-2.1) 11/03/2018 15:52:27.259 --------------------------------
Command from Aircraft:3986E5 (airborne) to GroundD:2198B7 
Frame-I: Ns:0 Nr:0
ACARS
Aircraft reg: F-HBXF Flight id: YS7656
Mode: 2 Msg. label: Q0
Block id: 1 Ack: !
Msg. no: M36A

[#4 (F:136.975 P:-6.3) 11/03/2018 15:52:27.831 --------------------------------
Command from Aircraft:3946EC (airborne) to GroundD:2190F7 
Frame-I: Ns:1 Nr:0
unknown data

[#1 (F:136.725 P:-3.5) 11/03/2018 15:52:28.240 --------------------------------
Response from Aircraft:406321 (airborne) to GroundD:1191EA 
Frame-S: Nr:4 RR

[#3 (F:136.875 P:-5.8) 11/03/2018 15:52:29.009 --------------------------------
Command from Aircraft:398517 (airborne) to GroundD:27CB21 
Frame-I: Ns:5 Nr:6
unknown data

[#4 (F:136.975 P:-5.0) 11/03/2018 15:52:29.006 --------------------------------
Command from Aircraft:440176 (airborne) to GroundD:1098CA 
Frame-I: Ns:5 Nr:6
ACARS
Aircraft reg: OE-IJF Flight id: U287HY
Mode: 2 Msg. label: H2
Block id: 5 Ack: !
Msg. no: M60A
Message :
02A111552LFRSLPPRN47097W001372111532  85P112     131P107205018G     185P097209026G     239P087215031G     292P072214037G     339P065220041G     378P052221044G     406P042226047G     427P035222046G     448P03022
Block End

[#2 (F:136.775 P:-6.6) 11/03/2018 15:52:29.357 --------------------------------
Command from Aircraft:461FA1 (airborne) to GroundD:280645 
Frame-I: Ns:4 Nr:7
unknown data

[#1 (F:136.725 P:-2.5) 11/03/2018 15:52:29.359 --------------------------------
Command from Aircraft:440630 (airborne) to GroundD:11989A 
Frame-I: Ns:1 Nr:4
unknown data

Compilation

vdlm2dec must compile directly on any modern Linux distrib. It has been tested on x86_64 with fedora 27, on tegra with Ubuntu 14.04.5

It depends on some external libraries :

• libusb
• librtlsdr for software radio rtl dongle input (http://sdr.osmocom.org/trac/wiki/rtl-sdr)
• libairspy for airspy (https://github.com/airspy/airspyone_host)

Make

for rtl-sdr

make -f Makefile.rtl

for airspy

make -f Makefile.air

Frequency correction for rtl-sdr

1. when receiving a message ex : [#1 (F:136.725 P:-3.7) 26/01/2018 21:34:57.633 -------------------------------- read the ppm displayed in P: field.
2. Guess an average, round to near integer
3. set the -p option as the opposite of this number (ex : -p 4 )

Acarsserv

acarsserv is a companion program for vdlm2dec. It listens to acars messages on UDP coming from one or more acarsdec processes and stores them in a sqlite database.

See : acarsserv

Note : vdlm2dec could only send packet over the network on json format. It does not support the acarsdec old binary format.

Copyrights

vdlm2dec and acarsserv are Copyright Thierry Leconte 2015-2018

These code are free software; you can redistribute it and/or modify it under the terms of the GNU Library General Public License version 2 published by the Free Software Foundation.

They include cJSON Copyright (c) 2009-2017 Dave Gamble a nd cJSON contributors