New ACARS data mode

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popnokick

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There appears to be a new high(er) speed digital mode being used now for ACARS... at least in my area where I hear them on 129.350 mHz. For years I've heard the ACARS data bursts on 129.35. In the past week I've noticed that they have changed to what sounds like a much higher data rate burst. Sorry - wasn't decoding them before, and have not tried the "new" data mode I'm hearing.
 

dlwtrunked

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There appears to be a new high(er) speed digital mode being used now for ACARS... at least in my area where I hear them on 129.350 mHz. For years I've heard the ACARS data bursts on 129.35. In the past week I've noticed that they have changed to what sounds like a much higher data rate burst. Sorry - wasn't decoding them before, and have not tried the "new" data mode I'm hearing.
Could it be VDL2? The only frequency I have seen for that is the 136.975 MHz listed at
Receiving VDL Mode 2 with MultiPSK and the RTL-SDR - rtl-sdr.com
 

popnokick

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129.350 is an ARINC freq, and they are one of the supporting contractors for FANS. And I think it could just as easily be VDL2 mode. I'm going to see if I can find an audio sample....
 

popnokick

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Well, there's a VDL2 sound sample here (search for "VDL") -
Search database - Signal Identification Wiki
The description on that page is good, but the sound byte they have doesn't sound like what I'm hearing. Maybe it's a bad sound file on the page.
If it is VDL2, ARINC has recently begun using it on 129.35 (vs the old ACARS mode).
 

dlwtrunked

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Well, there's a VDL2 sound sample here (search for "VDL") -
Search database - Signal Identification Wiki
The description on that page is good, but the sound byte they have doesn't sound like what I'm hearing. Maybe it's a bad sound file on the page.
If it is VDL2, ARINC has recently begun using it on 129.35 (vs the old ACARS mode).
The signal is 25 kHz wide and will sound somewhat different depending on the mode and bandwidth of the receiver but it should sound like a short pulse is VDL2.
 

737mech

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ACARS bandwidth 25kHz? Or just talking about the VDL-2 bursts? I decode in auto from my bct-15x but could try a direct 25 step if that's a better way?
 

ATCTech

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I'm seeing regular ACARS on 129.350 here near Toronto, with virtually all traffic being from eastern Michigan through to central New York and northern Pennsylvania.

I will point out that this appears to be a secondary SITACom ACARS frequency by the players I'm seeing on it, not RC-ARINC. In particular, Delta, FedEx, UPS, JetBlue and Virgin America are all on both 129.350 and 136.850, the primary SITACom frequency for North America. Here's a Republic ('Brickyard') flight that was on 129.350 inbound to Toronto from the southwest issuing a Q0 command (Link Test - looking for a ground station response):

[12/1/2016 11:02:22 PM]
YX3656 (N647RW) [Q0:8:M02A] MODE:2
<<< Link Test >>>

Then doing the same on 136.850 a few seconds later:

12/02/16 04:03:20 UTC
Mode: 2 Identifier: N647RW Ack.: {NAK}
Message type: Q0 (Link Test) Block: 9
Message: M03AYX3656

(I have 2 receivers running on 2 different ACARS decoders at the moment)

FWIW, reports in recent months from Europe confirm multiple VDL2 frequencies are now in use, but to date they all reside in the 136.0 -136.975 MHz range. A Google search will turn up frequency planning documents going back nearly a decade on expansion of VDL services and certainly the first phase was/is to relocate conventional ACARS away from 136.0 to 136.975 MHz and provide guard bands (in other words 50 kHz separation) between VDL channel assignments in that range.

Cheers!

Bob
 
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