Decoding P25 with SDR#, DSD, and RTLSDR

Posted on Wednesday, June 6th, 2012 in digital radio data, open source, RF, SDR by the machinegeek

This is another illustration of the amazing utility of the RTL-SDR and SDR# software. Here proct0r links the output from SDR# to a program known as DSD. DSD is an open source command line program originally coded in C by anonymous for Linux for the purpose of decoding digital protocols via a PC soundcard. The program accepts audio taken from the discriminator output from a scanner or amateur radio receiver fed to the soundcard input. DSD is then run (using the appropriate arguments, depending on the mode and parameters involved) with the resulting demodulated speech directed to the soundcard output jack. Additionally, various protocol decodes (P25 among them) provide a running display of certain packet data in the terminal window. DSD relies on the libraries contained in the required MBELIB package.

It is highly recommended that all RF hackers, whether using an SDR or conventional receiver, become acquainted with these programs and examine the Linux program source code. For more information and downloads of DSD and MBELIB, visit the RadioReference Digital Speech Decoder page.

This entry was posted on Wednesday, June 6th, 2012 at 3:27 pm and is filed under digital radio data, open source, RF, SDR. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

6 Responses to “Decoding P25 with SDR#, DSD, and RTLSDR”

  1. Ken says:

    Hi, I am the owner and creator of this video. This is unfortunately a bad video of my P25 decode. My sound card has some “crackely” audio on stereo mix and I can’t figure it out. I have raised my antenna and got a better signal level on the local P25 system and now I am getting a 99% decode with some slight skipping due to I’m guessing some underruns somewhere in the audio chain. All I do is set the default audio devices and open up the executable and it works near 100% decode. In SDR# you have to put the filter order on 10, not the stock 400.

    Audio Sample from DSDforwin & SDR#:

  2. joe says:

    The f___ing video is PRIVATE and will NOT plat :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :( :(

  3. Mikey says:

    It appears that the files referenced here and in the RadioReference page are unavailable – MINUS says they don’t exist.

    Is there another source?

    • EschatologicalEngineer says:

      Mikey, I used this link: haven’t tried it out yet though. I’m going to once I solder a discriminator tap to my scanner. I can decode pocsag just fine without any issues so I didn’t think that I would need a baseband decoder but I figured I should go ahead and mod my scanner before going further down this path. Good luck!

  4. Kamil says:

    Can someone please post some instructions how to set this DSD properly (meaning exact command line commands) setting audio inputs / outputs ? I have a RTL SDR stick, and I’m able to receive signal using HDSDR and SDR#, when i run dsd.exe from command line it runs but does nothing when i can hear the undecoded signal. What I’am doing wrong?

    • rynius says:

      You shouldn’t hear the unencoded sound. Change the audio out in SDR# to VB driver you should should have downloaded and installed. I’m still getting mine setup, but received something this morning. Also, try scrolling at fine frequencies to tune in the signal. I just used the default settings on DSD+.

Leave a Reply

Notify me of followup comments via e-mail. You can also subscribe without commenting.

Recent Comments