NEXEDGE trunk system decoding

Status
Not open for further replies.

Jay911

Silent Key (April 15th, 2023)
Feed Provider
Joined
Feb 15, 2002
Messages
9,378
Location
Bragg Creek, Alberta
I have a brand new system very near where I work which appears to be NEXEDGE, 3 frequencies, rotating CC, with NXDN audio. Is anyone contemplating supporting decoding of the CC any time soon (DMR Decode or Unitrunker, say)?

If you want/if it can help, I can do a discriminator tap (PSR-800 style) recording for a good long period of time from my location at work, recording from the 800 to line-in on the netbook and Audacity.
 

SCPD

QRT
Joined
Feb 24, 2001
Messages
0
Location
Virginia
I'm looking into it. Scanning these will require a frequency agile scanner. Parking on a control channel that seldom moves won't cut it here.
 

Jay911

Silent Key (April 15th, 2023)
Feed Provider
Joined
Feb 15, 2002
Messages
9,378
Location
Bragg Creek, Alberta
Can you explain a little more on what you mean by this? The system near me sounds like a constant control channel on one frequency (but rotates through the three channels of the system on a regular basis, much like other trunk systems that rotate the CC). Does it hop around a lot more often than that? My experience over the past couple days is that it stays on the same CC for hours, possibly up to 24 at a time. I get the impression from what you're saying that it cycles more frequently than that, perhaps based on user activity?
 

inigo88

California DB Admin
Database Admin
Joined
Oct 31, 2004
Messages
1,990
Location
San Diego, CA
One variant hops control channels on every call grant.

Do you know if it follows the same "rest channel assignment" mode of operation the MotoTRBO Capacity Plus systems do (i.e. no system controller, just networking the repeaters together)? If so, they're really not that hard to follow, the channel grant process is just different. Instead of saying "everyone on this talkgroup, go here," it says "everyone not on this talkgroup, go to this new place and keep waiting there." Check out the Capacity Plus thread in the Digital Signals Decoding subforum if you haven't seen it yet. :)
 

Jay911

Silent Key (April 15th, 2023)
Feed Provider
Joined
Feb 15, 2002
Messages
9,378
Location
Bragg Creek, Alberta
I forgot my audio patch cable or I'd run a good long chunk of CC audio and/or some radio audio (tapped from the PSR-800) tonight.

I'm working again tomorrow night, and it's more likely that they will be working tomorrow so more activity will occur.
 

exkalibur

Member
Premium Subscriber
Joined
Aug 15, 2006
Messages
2,764
Location
York, Ontario
Is there not some way to "predict" where it'll hop to? How does a system radio know what frequency to use as the next CC, or does it just scan all programmed channels? Whatever logic the radio uses could easily be reproduced in an application run on a PC.
 

inigo88

California DB Admin
Database Admin
Joined
Oct 31, 2004
Messages
1,990
Location
San Diego, CA
Is there not some way to "predict" where it'll hop to? How does a system radio know what frequency to use as the next CC, or does it just scan all programmed channels? Whatever logic the radio uses could easily be reproduced in an application run on a PC.

I don't know about NEXEDGE, but the TRBO Capacity Plus systems have an OSW that tells all nonparicipating radios that the current rest channel (the channel with the idle bursts) is being converted to a voice channel with talkgroup X and radio Y, and tells everyone not on that talkgroup to change to the logical channel number of the new rest channel (where the beacon data bursts resume). The system frequencies are stored into memory as LCNs, just like an LTR or EDACS system.

Hope this helps. I would love to see a program that dumps NEXEDGE data frames in the same way that DMRDecode dumps MotoTRBO data, but so far I haven't run into any NEXEDGE in this area.
 

SCPD

QRT
Joined
Feb 24, 2001
Messages
0
Location
Virginia
That's the system type I had in mind. If NEXEDGE doesn't roll control channels so often I should start there. The moving control channel isn't a problem - it just requires a tapped receiver that also supports computer control to chase the control channel. In case this isn't obvious to some, you can only get this data from a discriminator tapped receiver.

An inline receiver won't stream the data (perhaps an Arduino bitstream - some day).
 
D

DaveNF2G

Guest
Wouldn't simply leaving the CC receiver in Scan mode solve the rotating CC problem?
 

DaveH

Member
Joined
Jul 29, 2001
Messages
3,287
Location
Ottawa, Ont.
Is there not some way to "predict" where it'll hop to? How does a system radio know what frequency to use as the next CC, or does it just scan all programmed channels? Whatever logic the radio uses could easily be reproduced in an application run on a PC.

Not necessarily...the system controller knows which channels are available, but doesn't
(need to) broadcast this info, as long as the radios know how to find the next idle voice
channel.

As for free-scanning as Dave NF2G suggests, might work as long as the decoder doesn't
get confused when the CC changes, if it locks onto and starts decoding a VC.

Dave
 

DaveH

Member
Joined
Jul 29, 2001
Messages
3,287
Location
Ottawa, Ont.
Do you know if it follows the same "rest channel assignment" mode of operation the MotoTRBO Capacity Plus systems do (i.e. no system controller, just networking the repeaters together)? If so, they're really not that hard to follow, the channel grant process is just different. Instead of saying "everyone on this talkgroup, go here," it says "everyone not on this talkgroup, go to this new place and keep waiting there." Check out the Capacity Plus thread in the Digital Signals Decoding subforum if you haven't seen it yet. :)

Neat, sounds a whole lot like how the old Western Radio "Trac" system used to work with its DTMF
homing channel. Ironically that system locally was replaced years ago by MPT-1327 which is now giving
way, getting chewed at both ends, by TRBO and NexEdge.

Dave
 

Forts

Mentor
Database Admin
Joined
Dec 19, 2002
Messages
6,688
Location
Ontario, Canada
Does anyone have a link handy to that page with all the digital sound samples? There are a few channels around me which I suspect to be NexEdge but I really have no clue what it sounds like. And DSD doesn't seem to do anything with these ones..
 

Jay911

Silent Key (April 15th, 2023)
Feed Provider
Joined
Feb 15, 2002
Messages
9,378
Location
Bragg Creek, Alberta
Digital Modes Samples

Naturally the system I am near is quiet tonight. DSD 1.4.1 on autodetect once gave me a little brief X2-TDMA burp, but nothing substantial. I have tried it with -fi (decoding only NXDN 4800 frames) but either there has been no traffic, or the decoder isn't able to do anything with that.

I will try a few other things before switching over to the other computer, and recording some discriminator-tap audio of the control channel. If either of the voice channels come active, I'll try to plug DSD back in.
 

Forts

Mentor
Database Admin
Joined
Dec 19, 2002
Messages
6,688
Location
Ontario, Canada
Thanks, I actually found that page just after making that last post. The ones I suspected of being NXDN are indeed control channels by the sounds of it. So now I guess I need to find the voice channels that go along with it and see if DSD will do anything with them.
 

Jay911

Silent Key (April 15th, 2023)
Feed Provider
Joined
Feb 15, 2002
Messages
9,378
Location
Bragg Creek, Alberta
Sounds like the system is idle right now - not surprising considering they're construction workers working for the federal government. ;)

I tried to record some tapped audio, 3 files x 10 mins or so each. My reception is not 100% inside the building. Some time soon, I'll go over to an area near the construction site and get a better signal (preferably during working hours).

If I understand Rapidshare properly, this should be a link to a zipfile containing the above MP3s (total size about 33MB): https://rapidshare.com/files/1545548828/Ellis-Don-NEXEDGE.zip
 

DaveH

Member
Joined
Jul 29, 2001
Messages
3,287
Location
Ottawa, Ont.
Just over a year ago across the river, MRC de Papineau started up its NXDN/NexEdge
system on VHF. Every repeater transmits continuously; do I assume it is conventional
as there seems to be no CC/VC setup? I also see a bunch of conventional simplex
channels added.

TAFL shows all of these as 4kHz BW which I presume is 4800bps. From what I read
in the DSD Wiki, it doesn't do so well decoding the lower speed. Jay, I checked TAFL
on your frequencies; don't see the changes yet as they are on existing channels,
not new assignments.

Best verbal descrption I can give of the idle noise would be a muffled clattering sound.

Dave
 
Status
Not open for further replies.
Top