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  1. #1
    Join Date
    Aug 2005
    Location
    Cape Cod, Massachusetts
    Posts
    8,119

    Default P25 Decoding via Software and Discriminator Tap

    Using Ubuntu 9.10 Linux and the information and software in the following links I've managed to get some rudimentary P25 decoding using a discriminator output.

    Original RR thread: http://forums.radioreference.com/tru...er-mbelib.html

    Newest RR thread: http://forums.radioreference.com/tru...-released.html

    RR Wiki Page: http://wiki.radioreference.com/index.php/DSD

    In addition to P25 decoding the software apparently works with some success with other digital voice modes. See threads for details.

    I am getting choppy but intelligible decodes with it. As mentioned it does require Linux but reportedly a port to Windows is in progress by someone. If you run Linux and have P25 signals in your listening range I'd encourage you to give it a try. Post #30 in the original thread offers a good outline for compiling the software and running it. I followed it verbatim and it worked for me, and my knowledge of Linux is "novice" to say the least.
    Scott - Scan New England Webmaster

  2. #2
    Join Date
    Oct 2005
    Location
    Lynn, Essex Co.
    Posts
    766

    Default

    Hello,

    I find it interesting that the 1.3 version decodes Provoice. I should try it on the MBTA system.

    I have a DV Dongle which uses a real DVSI AMBE Codec chip. I want to see if I can feed the IMBE bits into it instead of the decode library and decode P25 voice. This should get around the software patents issue with DVSI.

    73 Eric

  3. #3
    Join Date
    Aug 2005
    Posts
    2,499

    Default

    Is it possible that someone would be able to come up with a deliverable for Uniden or GRE so that Pro Voice could be included in future scanners?
    We're peace loving people, we're not hunting trouble, but if trouble should find us, we'll stand up and fight.

  4. #4

    Default

    Quote Originally Posted by wb1hbu View Post
    Hello,

    I have a DV Dongle which uses a real DVSI AMBE Codec chip. I want to see if I can feed the IMBE bits into it instead of the decode library and decode P25 voice.
    According to DVSI, their AMBE chip will NOT decode IMBE. Yes, I know AMBE is supposed to be upwardly compatible, but apparently they've deliberately disabled IMBE decoding with their commodity AMBE chip (which is very low cost).

    Sad, but that's the story I got. OTOH, I can't say I know anybody who's actually TRIED it...

    Peter
    K1PGV

  5. #5
    Join Date
    Oct 2005
    Location
    Lynn, Essex Co.
    Posts
    766

    Default

    Hello,

    I was able to get P25 decodes but no ProVoice. I had some notes from last year when I looked at Provoice and noticed the sync was different than what is in the program. I changed the sync, recompiled, and now get good ProVoice decodes. It looks like the EDACS EA systems has a different format for the header to handle the increased number of identifiers.

    I have not tried the DV Dongle yet. From my experiments the DV Dongle does not support the P25 bit shifting but I am going to modify the dsd program to write the bits to a file without any error correction bits. The error correction and bit shifting can be done in the computer.

    73 Eric

    73 Eric

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