ACARS v VDL2 ground stations

[peter1066]

Here in S.E.UK one facet of ACARS for me is logging the Ground Stations and seeing just how far is received, sporadic E helps at times. Identifying the SQ Uplinks is not too bad with regular ACARS as msgs look typically like this one of Dussedorf Germany - I have added spaces in the message line for clarity. This was on 131.725 MHz using Multipsk V4.28

31/03/15 18:03:36 UTC
Mode: x Identifier: Ack.: {NAK}
Message type: SQ
Block:
Message: 02XS DUS EDDL 05117N00646E V136975/

I'm now trying to make sense and identify SQ Uplinks on VDL2 traffic on 136.975 MHz. I receive many, many messages on this VDL2 channel like below. can anyone assist in what (I'm guessing) hexa "10919A" translates into in text and what a "typical" VDL2 Uplink looks like ?

04/04/15 00:01:28 UTC
Destination address (hexa): 10919A (Ground Station, delegated address)
Source address (hexa): 40622B (Aircraft airborne , command frame)
I (Information) frame N(R)=0 N(S)=0 P=0
ACARS message ("AOA")
Data (hexa): FFFF0132AEC7AD45DA54541551B03702D3B032C1D532B531C7CD83DA7C7F
Mode: 2 Identifier: G-EZTT Ack.: {NAK}
Message type: Q0 (Link Test) Block: 7
Message: S02AU251GM


Regards, Peter1066

 

[ATCTech]

10919A is the address of the intended receining ground station, (not the ultimate destination of the message content) as this is a downlink message from the aircraft. Each G/S site has a unique hex address, as does each aircraft, in this case 40622B. The aircraft hex code will be the same address you'd see in ADS-B decoding when the aircraft transmits. ADS-B ground stations do not (yet) transmit. Future flavors of ADS-B will likely change that.

A VDL-2 SQ message will be addessed to FFFFFF, which means in effect "all stations", with the source address being as I mentioned above.

Here are the 3 Toronto CYYZ VDL-2 SQ messages: FWIW, a leading "1" translates to an ARINC site, a leading "2" is a SITA site. I honestly believe this is a global standard for the 2 providers, but some outside of North America will argue that. <G> Someday I'll find a reason to call my ARINC contacts on official business and ask that question as an aside.

02/16/15 20:34:36 UTC
Broadcast address (hexa): FFFFFF (All aircraft)
Source address (hexa): 1030AA (Ground Station, delegated address , command frame)
XID (Exchange Identification) frame F=0
Data (hexa): 8280001C0109383838353A31393933020200010303208480050207D8060207D8F0001F000156040120C1044359595AC406000000000000C504FC020000C8031B5CE4
Ground station (+/- 3'): 43°42'N 079°36'W


02/16/15 20:34:51 UTC
Broadcast address (hexa): FFFFFF (All aircraft)
Source address (hexa): 1024FA (Ground Station, delegated address [CYYZ Toronto] , command frame)
XID (Exchange Identification) frame F=0
Data (hexa): 8280001C0109383838353A31393933020200010303208480050207D8060207D8F0001F000156040120C3044359595AC406000000000000C504FC020000C8031B5CE4
Ground station (+/- 3'): 43°42'N 079°36'W


02/16/15 20:35:53 UTC
Broadcast address (hexa): FFFFFF (All aircraft)
Source address (hexa): 2CE757 (Ground Station, delegated address [CYYZ Toronto] , command frame)
XID (Exchange Identification) frame F=0
Data (hexa): 828000140109383838353A3139393302020001030320A488F0001F000156040120C1044359595AC406000000000000C50494000000C8031B5CE4
Ground station (+/- 3'): 43°42'N 079°36'W

Cheers!

Bob

 

[peter1066]

Thanks for the reply and the sample VDL-2 SQ messages locally there.
So if i'm reading it right, all(?) G/S begin with "Broadcast address (hexa): FFFFFF (All aircraft)"
with a hexa source address and a leading 1 for ARINC and 2 for SITA checking some recent aircraft logs here reveal source addresses being called either have a leading 1 or 2 as you say - a few shown here
10900A 10900A 10909A 10914A 10988A
214AB7 2190F7 251657 261EF7 262257
Presumably the rest of the hexa group denotes something which may ID the ground station.
I'll keep building up the VDL-2 logs looking an SQ message - I'm not very close to an airport, but I get success on the ACARS channels

Cheers,

Peter

 

[DaveNF2G]

Is there a list of ground station hex codes somewhere, or is it being developed on-the-fly by hobbyists?

 

[ATCTech]

Dave, best I know of so far is the small list compiled by Patrick from submissions from users on the MultiPSK list. I'm guessing the fact of needing the paid version of MultiPSK and no other software options limits the popularity so far.

Bob

 

[ATCTech]

Hi Peter,

That was me that replied on the other list so we can keep our conversation here if you like.

The G/S only uses FFFFFF for a squitter broadcast message in normal operation, otherwise the destination address will be the ICAO hex code for the aircraft. I suspect the system can do a full broadcast message with actual content if required, but that's just a guess on my part.

Obviously you're using MultiPSK so determining the uplink address is correct from your results so far. You'll never identify the location based soley on the address as there's no online compilation yet so Patrick can't integrate a common-language name for each ident yet. Because range is limited being close to the airport and (depending on your country's laws) the availablilty of online license data is a big help. Here in Canada the licenses are on the government's public web site, including lat/long info, so cross-referencing is fairly simple. As the SQ uplink contains lat/long it's a giveaway of the location, you just need to be close enough to capture it. From a downlink message, that's a problem for all of us without a reference document, especially when there are multiple addresses at some locations (like here).

Bob

 

[peter1066]

Hi Bob,

Yes fine we'll continue here.

Multipsk 4.28 is main software in use. Ant is a discone @ 30ft. Have a good location and get "ordinary" VHF ACARS ground station reception up to 300km+ maybe with a little sporadic E help. It does involve searching through thousands of the usual downlink logs, (of course I have unticked the "no Uplink" box in Multipsk!) Could do with a "no Downlink option here!)
Have attached a list of received G/S here recently for interest sake.

So I wonder if VDL-2 will offer the same possibilities of ground station reception, I have suggested to Patrick an option for only G/S on screen - if that's possible and he has put it on his wish list.
From what you saying getting the SQ link with with lat/long coordinates in the message is the giveaway.
Now is there a text string unique to VDL-2 ground stations (like regular ACARS "Message type: SQ") to use for searching thru masses of aircraft downloads ??

Seems that ARINC and SITA don't make their info easy to get at!

Did notice this link for some NZL VDL-2 info

HFAero · VDL2 Mode


Cheers,

Peter

 

[DaveNF2G]

It might be easier if MultiPSK could be pointed to a file with the info, as is done for SELCAL addresses.

 

[ATCTech]

Hi Bob,

Yes fine we'll continue here.

Multipsk 4.28 is main software in use. Ant is a discone @ 30ft. Have a good location and get "ordinary" VHF ACARS ground station reception up to 300km+ maybe with a little sporadic E help. It does involve searching through thousands of the usual downlink logs, (of course I have unticked the "no Uplink" box in Multipsk!) Could do with a "no Downlink option here!)

Peter

Peter,

I think you'll find the Uplink button (when selected on) is designed to show only uplink messages and no downlinks. I made the same mistake until Patrick corrected me.

Bob

 

[peter1066]

Bob,

In VHF ACARS there is a "No Uplink" button, when selected Downlinks still fill the screen here?
I know they can be turned off in VDL-2

Peter

 

[ATCTech]

I thought you were referring to VDL-2, sorry. I'm going to take my laptop to work on the weekend and I'll capture a bit of VDL-2 data for you from within 1 km of the G/S. You'll be amazed how busy it is. I also want to confirm the SQ messages occur every 2 minutes from each G/S if idle as they do with conventional ACARS. I'm 99.9% certain they do.

Bob

 

[peter1066]

Patrick did say giving the option to turn off the G/S in the VHF ACARS mode was on his to do list.
Looking forward to seeing that VDL-2 data.

Peter

 

[ATCTech]

I'm decoding live right in the middle of CYYZ Toronto now. Here's a list of the time stamps of the SQ messages from the 3 Toronto G/S collected in the first 20 minutes of decoding. You'll note that once in a while when a particluar G/S is busy it will skip a SQ cycle, but for the most part the timing is ~2 minute intervals for each, exactly like conventional ACARS. Station idents are followed by the UTC time stamp of the SQ message:

1024FA (Station)

185047 HHMMSS
185228
185420
185603
185756
185940
190136
190336
190520
190710
190902



1030AA (Station)

185047 HHMMSS
185235
185421
185814
185958
190155
190352
190535
190912



2CE757 (Station)

185156 HHMMSS
185412
185615
185820
190018
190200
190630
190850

The long and short of this is if you don't see a SQ message in 10 minutes of decoding you're not going to see any other G/S traffic from that station ident, full stop.

The log file for MultiPSK over a 2 hour period today is in excess of 1MB of text for ONLY uplink messages, and Saturday isn't anywhere near as busy as Thursday and Sunday here.

Bob

 

[ATCTech]

Peter,

Let me know if you'd like the MultiPSK VDL-2 log file I saved from yesterday. I ran Uplinks only for about 3 hours then switched to full decoding. It's about a 3MB text file.

Cheers!

Bob

 

[peter1066]

Bob,

Yes please! 3MB download is no problem, it will be interesting to study - though the evidence seems to be stacking up against any VDL-2 G/S reception at this QTH!

Cheers

Peter

 

[ATCTech]

PM me your email address and I'll get it right over to you.

Bob

 

[peter1066]

peterconway.ndb@talktalk.net

Cheers

Peter

 

[ATCTech]

It's in your email now I suspect!

Bob

 

[peter1066]

File received fine, will reply to your offline msg later

Thanks

Peter