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Aircraft Data Decoding - A forum to discuss decoding the various data transmissions such as ACARS, Mode-S, ADS-B, etc.

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Old 09-22-2017, 11:28 AM
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Default Monitoring ACARS

Hi, I have been listening to regular aviation traffic for years but now I would like to try monitoring ACARS. What is a good reference on setup, equipment, software etc?

Thanks
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Old 09-22-2017, 1:07 PM
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Quote:
Originally Posted by joncleve View Post
Hi, I have been listening to regular aviation traffic for years but now I would like to try monitoring ACARS. What is a good reference on setup, equipment, software etc?

Thanks
I use ACARSD, which is mentioned in this article -
https://www.rtl-sdr.com/rtl-sdr-radi...ta-with-acars/
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Old 09-22-2017, 2:12 PM
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Thank you.
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Old 09-22-2017, 2:53 PM
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ACARSD is here,

ACARS - Free ACARS decoder for Linux & Windows - acarsd

I used it with a stand-alone scanner feeding the audio into the line input of a laptop, works well.
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Old 09-23-2017, 3:03 PM
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I use MultiPSK, but the licensed version. An SDR dongle is used for a receiver.
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Old 10-01-2017, 10:06 AM
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Does anyone know if ACARSD has been updated since version 1.70?
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Old 10-01-2017, 10:08 AM
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Also, been about a year since I monitored ACARS, I recall the frequency 136.850 being busy it was listed as SITA North American Frequency. Does anyone know if this frequency is still active, I've received nothing and I'm in the Northeast US. Also does anyone have an updated list of know ACARS frequencies?
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Old 10-01-2017, 10:13 AM
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Quote:
Originally Posted by AZ645 View Post
Also, been about a year since I monitored ACARS, I recall the frequency 136.850 being busy it was listed as SITA North American Frequency. Does anyone know if this frequency is still active, I've received nothing and I'm in the Northeast US. Also does anyone have an updated list of know ACARS frequencies?
136.85 was also really active in Atlanta and has also went silent. Now 129.35 seems to be the active freq in the ATL airspace. Give that a try and let us know how it works.
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Old 10-01-2017, 2:00 PM
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Quote:
Originally Posted by AZ645 View Post
Also, been about a year since I monitored ACARS, I recall the frequency 136.850 being busy it was listed as SITA North American Frequency. Does anyone know if this frequency is still active, I've received nothing and I'm in the Northeast US. Also does anyone have an updated list of know ACARS frequencies?

ACARS - The RadioReference Wiki
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Old 10-01-2017, 3:39 PM
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I think you'll find most of the 136.xxx legacy ACARS frequencies have been abandoned in anticipation of additional VDL2 capacity. Here in Canada, SITA moved all of their sites nationally from 136.850 to 131.725 a couple of months ago. The others have been silent in the eastern Great Lakes region for considerably longer than that, monitoring them from north of the border at least.

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Old 10-01-2017, 5:21 PM
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ATCTech,

Thanks, that explains it. I am in Western NY so pick up lots of YYZ bound flights. Does the daily Alitalia flight from FCO use SITA or do the ACARS frequencies vary?
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Old 10-01-2017, 5:25 PM
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Just tried 131.725, lots busier, Thanks for all the info.Any decoders out there for VDL2? I've used MultiPSK with an SDR but not as nice as ACARSD.
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Old 10-01-2017, 8:21 PM
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If you have the paid version of MultiPSK then you have one of the only VDL-2 decoding programs available. Although it can be used with certain receivers connected to your PC, it works best with an RTL 'stick' as MultiPSK can control it's tuning etc. directly.

Regarding your question about airlines versus what provider they use for legacy ACARS, for any one operator it's going to be one or the other 99.9% of the time as the airline/aircraft operator is paying for the service. Coverage is so similar that it would be pointless paying for both. The aircraft equipment is programmed with a primary frequency to log onto the network, so that's going to be 131.550 for RC/ARINC or (I'm guessing based on recent changes) 131.725 for SITA, in North America anyway. (BTW, there are a couple of smaller regional providers in Japan and eastern Asia.)

Alternate frequencies for any particular exchange are sent by the network as a message like this:

10/02/17 01:02:09 UTC
Mode: 2 Identifier: C-FMWV Ack.: 1
Message type: :; (Uplink - Command change frequency) Block: P
Message: 130025

The radio for the data link system in the aircraft will automatically re-tune to (in this case) 130.025 MHz.

If you're close enough to an ACARS ground station, the squitter (SQ) message will tell you the provider using the frequency. Look at the 4th character in the MESSAGE field, it will be either A (RC/ARINC) or S, SITA. In this case the message is also ended with /ARINC:

10/02/17 01:07:44 UTC
Mode: 2 Identifier: Ack.: {NAK}
Message type: SQ
Block:
Message: 02XAYYZCYYZ24340N07937WV136975/ARINC


Here's a SITA squitter:

10/02/17 01:10:32 UTC
Mode: 2 Identifier: Ack.: {NAK}
Message type: SQ
Block:
Message: 02XSYYZCYYZ04340N07937WV136975/

Note that they don't bother to encode /SITA at the end.

You'll also see reference to 136975 in both of these. This automatically identifies the ground station location as also providing VDL-2 service, which uses that frequency as it's primary frequency globally and unlike legacy ACARS, at this point it's common to BOTH PROVIDERS.

A squitter from a non-VDL2 SITA ground station looks like this:

10/02/17 01:12:52 UTC
Mode: 2 Identifier: Ack.: {NAK}
Message type: SQ
Block:
Message: 00XS

And from RC/ARINC it looks like this:

10/02/17 01:21:51 UTC
Mode: 2 Identifier: Ack.: {NAK}
Message type: SQ
Block:
Message: 01XAYHMCYHM2ARINC

Notice the RC/ARINC squitter identifies the ground station, in this case YHM/CYHM, Hamilton Ontario.

Finally, the daily AZA flight from here back to FCO just started its log-on sequence to legacy ACARS seconds ago and it is with SITA on 131.725. It's still at the gate at this point.

10/02/17 01:38:48 UTC
Mode: 2 Identifier: EI-EJH Ack.: {NAK}
Message type: Q0 (Link Test) Block: 6
Message: S20AAZ065F

And then it logged onto VDL with SITA as well. (2CE757 is the identifier of the CYYZ SITA VDL-2 ground station.)

10/02/17 01:46:44 UTC
Destination address (hexa): 4CA87D (Aircraft)
Source address (hexa): 2CE757 (Ground Station, delegated address [CYYZ Toronto 43°42'N 079°36'W] , On the ground , command frame)
I (Information) frame N(R)=2 N(S)=1 P=0
ACARS message ("AOA")
Data (hexa): FFFF0132AE4549AD454AC831DF7FC2839B6A7F
Mode: 2 Identifier: EI-EJH Ack.: 1
Message type: _ (General response. Demand mode. No information to transmit) Block: B
Message:



Cheers!
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Last edited by ATCTech; 10-01-2017 at 8:55 PM..
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Old 10-02-2017, 8:26 AM
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I am still hearing 136.850 traffic from the Albany area. The new frequency is very busy. So far, no VDL2 beyond .975 yet.
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Old 10-02-2017, 9:55 AM
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HI Dave,

Are the messages anything more than repeated Q0 (Link Test) or unacknowledged position reports? That's ll I see from up here since the switch which means there are no ground stations on the frequency.

Cheers!
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Old 10-03-2017, 8:42 AM
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I get occasional position plots.
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Old 10-03-2017, 3:10 PM
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Ok Dave, thanks, I see repeated position reports as well. mostly from bizjets that haven't been updated to the new main frequency. Most of them repeat multiple times until the CMU gives up from no response form the G/S. That says to me that 136.850 is a dead issue.

Cheers!
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Old 10-11-2017, 6:38 PM
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I think you're right. I watched 136.85 for most of the past weekend and only saw transmissions from one Netjets aircraft.
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Old 10-15-2017, 2:10 PM
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just got back into ACARS this week.
only freq I'm getting action on is 131.55
wish I had a list of KG-ACARS icons, still trying to figure out will play with this week
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Old 10-15-2017, 3:32 PM
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This is directly from the KG-ACARS English help file.

About tool-bar icons: From the left to right.
1: Aircraft list window: Opens/closes the aircraft list window/ Details will follow.
2: Aircraft information window: Displays the information of the flight/equipments most recently received. / Details will follow.
3: Aircraft search window: You can input desired aircraft data so that the software will alert by display and sound when the selected aircrafts’ signals are received. / Details will follow.
4: Text window: Opens/closes the Text window / Details will follow.
5: Plot display: Turns on/off the plot lines of the flight.
6: Shows only the most updated flight plot when ON is selected. 
7: Flight-data selector:
l FL: Flight level = Indicates flight level under the plot points.
l TIME: Time = as above, shows the local time of the latest signal received.
l DATA: Flight data = as above, shows airport of dep/dest and type of equipment. Such information is not automatically generated therefore updates of files in DATA folder is necessary.
8: Triangles: Moves the map to the related direction. The map can be moved by simply dragging to the direction you wish with your mouse on the map. Dragging the mouse on the map will also move the map.
9: Zoom in/out/size of map: Use these to select the map size.
10: VOR-DME/VORTAC/NDB/WAYPOINT/AIRPORT : Use these icons to select AIRNAV positions you wish to turn on/off on the display.
11: VOR/NDB/NAV : Use these icons to select airway lines you wish to turn on/off on the display.
12: Company selector: Newly received carriers are added to the list in each operation. Select the carrier you wish to monitor on the screen. Select “all” to indicate all plots.
13: Monitor: Click this to monitor the sound.
14: IP: Use this to connect to the server.

And this is the right-click menu interpretation:
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