conventional P25 channel decoding

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gary123

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Like many others my local PD is using conventional p25 (encrypted). I have already decoded the NAC but was wondering if it is possible to decode additional info such as user ids etc. If it will help I am prepared to look at raw dumps of the data to attempt to identify packets or information. Any suggestions would be apreciated.
 

WayneH

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It's actually already documented on what to look for in the raw information. I think the only reason the hobbyist community hasn't tackled it is the soft process of turning the raw audio in to bits. Those of us familiar with kNACk know it doesn't work more than it works.
 

cg

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I am not sure what equipment you are using but the newer Uniden scanners will do unit IDs in trunking. There was a reference to setting the conventional channels up as a single channel trunked system and using the unit ID. I can't find the post but you could search for it. If you are looking to do it within freeware, then disregard.

chris
 

Squad10

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Like many others my local PD is using conventional p25 (encrypted). I have already decoded the NAC but was wondering if it is possible to decode additional info such as user ids etc. If it will help I am prepared to look at raw dumps of the data to attempt to identify packets or information. Any suggestions would be apreciated.
I suggest:

Documents: Theses
 

gary123

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I am using Unitrunker on a 760 through a data slicer this gives me exellent waveforms. I also have a 996t and a motorola maxtrac all configured for data output.

It's actually already documented on what to look for in the raw information.
Do you have a link to the raw info? and dumping it. Also any info on the format of the data would be good. If I could docode something like below (its a c&p from a differnet topic but is along the lines of what im looking for)

Frame Sync: 0x5575f5ff77ff
NID codeword: 0x37258af0f9b29f8c
Network Access Code: 0x372, Data Unit ID: 0x5
Raw IMBE frame: 0x2922b5eeabc05f22c3222ad0e622e522179e
Raw IMBE frame: 0x1a22ffcca32c42e2ee5525ec85f2222c2222
etc

[Quote} Those of us familiar with kNACk know it doesn't work more than it works [/Quote]

so far kNACk is the only program I have for decoding NACs I am not aware of the issues with it.

I am prepared to look into compiling the raw audio into bits

cg

There was a reference to setting the conventional channels up as a single channel trunked system and using the unit ID
I will look for this post, If you can find it that would help too. I did find some posts on using the ID frature on the XT models but since I dont have one of them I cant go any futher.
 
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WayneH

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Do you have a link to the raw info? and dumping it. Also any info on the format of the data would be good. If I could docode something like below (its a c&p from a differnet topic but is along the lines of what im looking for)
It's detailed in TIA/EIA Project 25 documentation which unfortunately requires a subscription to read. I can't seem to find what I want otherwise I'd paste the info.

kNACk is very picky about waveforms but since I have gear that decodes them I haven't tried different receivers to see which work the best.
 

KA1RBI

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If I could docode [sic] something like below (its a c&p from a differnet topic but is along the lines of what im looking for)

Frame Sync: 0x5575f5ff77ff
NID codeword: 0x37258af0f9b29f8c
Network Access Code: 0x372, Data Unit ID: 0x5
Raw IMBE frame: 0x2922b5eeabc05f22c3222ad0e622e522179e
Raw IMBE frame: 0x1a22ffcca32c42e2ee5525ec85f2222c2222
etc
The above output came from our c4fm-decode.py program, written by Michael Ossman (Mossman). You're welcome to join and contribute to our project - ref: yahoo grp op25-dev

73

Max
 

SCPD

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If you're looking for the P25 specs but don't want to PAY for them (and you live in a big city), go to your public library. You might be surprised.
 

gary123

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If you're looking for the P25 specs but don't want to PAY for them (and you live in a big city), go to your public library. You might be surprised.

I have looked at several documents. Part of the trouble (fun) is getting the info I want. I am still doing research.

KA1RBI I know :) I was just using that code snipet as an example of the type of info im looking for on the conventional p25 systems.

I know that there is a TGID, a WACN, and a unit (soft ID) id sent. this is the data im trying to locate and decode.
 
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