Utility to Help Identify/Decode Random Digital Traffic??

[aka_ramon]

There's a system near me on the VHF high band, non-trunked, that has P25 audio and some sort of digital data (that I understand is UDP/IP encapsulated).

I don't know the data speed (2800, 3600, 4800, or 9600) or even the modulation type (well, I know my 396t can receive the P25 audio, so that limits the modulation type to C4FM or CQPSK, I guess).

I'm wondering if there's a utility (1) that'll help me figure out the unknowns about this system, and (2) dump the IMBE and/or IP data packets in binary and/or hex?

Always trying to learn... TIA,

R

 

[SCPD]

There's a system near me on the VHF high band, non-trunked, that has P25 audio and some sort of digital data (that I understand is UDP/IP encapsulated).

I'm wondering how you know that.

I'm wondering if there's a utility (1) that'll help me figure out the unknowns about this system, and (2) dump the IMBE and/or IP data packets in binary and/or hex?

I have not seen a program that does this. There's a couple of programs out there to dump the control channel packets to a file but not the voice packets or data packets. The effective throughput for confirmed data on a P25 channel is considerably less than 9600 bps.

-rick

 

[aka_ramon]

Thanks for the reply, Rick.

I'm wondering how you know that.

I assume you mean the "UDP/IP encapsulated" part of that sentence?

Well, you know... You read, you google, you read some more, you google some more...

I have not seen a program that does this. There's a couple of programs out there to dump the control channel packets to a file...

Interesting. I couldn't find anything either... heavy sigh... which surprised me.

Got any pointers on where I could or should start? I s'pose I should hook up a discriminator tap to one of my old analog scanners. Do any of the existing decoding programs have source available (yeah, I can code)? I can't imagine writing the fundamental input functions would be particularly "fun" so I wouldn't mind avoiding that part of the mess if at all possible.

Is there a better place to post these sorts of questions?

Thanks again,

R

 

[SCPD]

Got any pointers on where I could or should start?

First, please realize the territory you're getting into here. Do some digging on a program called MDTMon along with some of the potential issues with federal and state criminal code. I'm not saying it's illegal but it has been problematic for some - depending upon situation (like juristiction).

I s'pose I should hook up a discriminator tap to one of my old analog scanners.

Yes. Also, though not required but hardware that supports 96k samples per second are preferred (as opposed to the standard CD audio quality 44.1 k samples per second). Don't bother with a slicer - at least not for this application.

Do any of the existing decoding programs have source available (yeah, I can code)? I can't imagine writing the fundamental input functions would be particularly "fun" so I wouldn't mind avoiding that part of the mess if at all possible.

There's at least one program in beta that will have source available once the program is officially released. The code is under a GPL license.

Is there a better place to post these sorts of questions?

Probably not but you may want to try the GNU-Radio mailing list. There is additional GPL'd code there that may provide inspiration. Another GPL'd project is the SDR1000 but I can't suggest the SDR1000 because it is designed for HF ... it won't work above 60 Mhz or so.

-rick