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Thread: P25 type data bursts

  1. #1
    PRC148 No Longer Registered

    Default P25 type data bursts

    This has been a mystery for some time around here. We have been getting data on 165.0875 for the last two years. For the last year or more it sounded just like the hang timer on a P25 repeater about every 10 minutes, just a flat braaaaaap for about 5 seconds. Recently there is a change with a much longer packet with what sounds like data present on whatever the signal is. I have tried to demodulate it but it doesn't decode. It has that framing control sound, not a voice channel type of sound. I'm trying to get a recording to post as an example. I can't imagine what it could be unless it's some sort of digital paging (does that exist?).


  2. #2
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    I sure hope someone hasn't gone out and spent tens of thousands of dollars on a "state of the art" half-duplex 9600bps P25 data implementation. I like P25 radios for voice, just as much as everyone else. But the P25 data options are a joke. 1980s technology. No better than ham radio packet.

    x 10000000000000000

    Looking forward to more info once you have it available.

  3. #3
    PRC148 No Longer Registered

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    It's odd. I think it has to be fed in that range. I hooked up the PSR800 to get a recording but as luck has it for whatever reason the RX on the 800 is crap the second I hooked it up and I don't know why. I'm trying to grab the audio files now to see what they actually sound like.

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    Could it possibly be Trbo? To my ear at least when listening to a Trbo signal and a P25 signal on a analog radio they do sound similar with some variations. I know the feds wouldn't really use Trbo but hey you never know these days.

  5. #5
    PRC148 No Longer Registered

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    I am trying to get a recording. I will sit on it again tonight and listen.

  6. #6
    dxon2m No Longer Registered

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    Are you sure the PSR-800 doesn't have IF output enabled when you said it sounded crap?

    Couple fed P25 repeaters here does the same thing so you are not alone.

  7. #7
    PRC148 No Longer Registered

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    I was pulling the recording from the radio itself, not using the mic jack to record to another device. I will try to get a better recording of it again. It just goes on and on but doesn't seem to carry any voice traffic.

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    There is one Fed repeater in my area that has some activity on it from time to time and every once in a while I will catch a short little data burst on that freq

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    Could be text messaging, OTAR, packet data or call alert paging.

    What's the hang time on the repeater?

    Cold be a short data packet with a long repeater hang time.
    Cyrus

    Bubbles: I'd like to see that Red Blue Green c***sucker put one of those together, duct-tapin' it.

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    Quote Originally Posted by cyrus View Post
    Could be text messaging, OTAR, packet data or call alert paging. ~
    Add GPS location data to that list?
    Andrew

  11. #11
    dxon2m No Longer Registered

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    Is there any chance of decoding the data with tools like IF tapped scanner and wireshark?
    .

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    Yes. There is.

  13. #13
    dxon2m No Longer Registered

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    Could you elaborate a bit more?
    I would imagine I need to make "something" into a data stream that wireshark can recognize as a "protocol adapter". The IF tapped output is analog but what makes it into 1's and 0's so wireshark can understand?

  14. #14
    PRC148 No Longer Registered

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    I finally got a recording of it.

    http://snd.sc/O2Rv4F

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    Sounds a lot like an idle DMR channel to me. DSD does decode it as DMR idle/unknown bursts, but then DSD is a bit rough around the edges.

    Fed band DMR is relatively rare, a friend that might likely know has never seen it in the wild. There have, I hear, been reports of it.

    I've seen 165.0875 listed as AF, NPS, WHCA, BOIA; none of which would seem likely to use DMR...

    The mystery continues!

    [EDIT] BTW, I dig the pirate MilSat radio station recording!
    Last edited by safe; Sep 14, 2012 at 12:32 AM.

  16. #16
    PRC148 No Longer Registered

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    I got a good capture of a long bit of it tonight. It doesn't decode and the 996 doesn't show DAT or any other display indication.

    https://soundcloud.com/mancow-1/165-0875mhz

  17. #17
    PRC148 No Longer Registered

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    BTW, it makes reception much easier when the radio is connected to the antenna on top of this and linked with a 5 Mb connection.


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    Seems like a silly question, but have you tried listening to it with DMRdecode? Sounds like MotoTRBO to me.

  19. #19
    PRC148 No Longer Registered

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    No I haven't. I've not had much luck with those sound card type programs but I might give it a try. It sounded like P25 of some sort to me but it could very well be DMR.

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    Yep

    I agree with what Avery said x 2 - its 100% TRBO DMR, not APCO P25.

    Cheers,
    Matt

  21. #21
    PRC148 No Longer Registered

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    Hmmm that's interesting. I wonder who would be on DMR on a freq like that?