RTL-SDR dsd tutorial: monitoring P25 digital voice

Posted on Sunday, April 21st, 2013 in digital radio data, RF, SDR, software by the machinegeek

The crew over at has posted a simple tutorial on using the RTL-SDR dongle and free SDR# and Digital Speech Decoder software (dsd) to monitor P25 digital radio voice comms. They describe, “Digital radio voice communications are becoming more commonly used in the radio spectrum. This is due to the various improvements offered over traditional analogue voice radio systems. Unfortunately for radio scanner hobbyists, digital radio is difficult to receive, as special radio scanners which can be expensive are required to decode the digital audio. Additionally, digital radio systems can be encrypted making it impossible for communications to be decoded by a hobbyist. However, most users of digital radio do not bother to encrypt their systems as it can introduce lag and extra battery drain in portable radios.

The most common digital speech codec is APCO P25, which dsd is able to decode. Dsd is also capable of decoding other common digital codecs such as DMR/MOTOTRBO and ProVoice which no hardware scanner is currently capable of.”

One part of this project that isn’t open source is their use of Virtual Audio Cable software to route the SDR# output to the DSD.

This entry was posted on Sunday, April 21st, 2013 at 6:00 pm and is filed under digital radio data, RF, SDR, software. 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 “RTL-SDR dsd tutorial: monitoring P25 digital voice”

  1. rasz says:

    still no D-STAR

    what a major effup to implement closed voice codec in HAM space

  2. Marc says:

    to rasz … this is free software and not the writers of DSD, SDR software, GNU software or anything… the fact that d-star is a proprietry bit of technology is
    the problem, please dont diss the software writers, it seems you *expect*
    everything to be available to you, no matter what. it isn’t, wont be, shouldn’t be
    and lack of respect shows little or no understanding of the issues involved.

    Thank the authors, encourage, donate, send bug reports and generally offer constructive help please. The work of free coders EVERYWHERE is changing minds and the tech world, and we Thank, Help and support them all in many ways.

  3. Marc says:


    this is free software and **lack of dstar voice is not the fault of** the writers of DSD, SDR software, GNU software or anything…

    • rasz says:

      Yes Mark you are right.
      I meant effup/scam by Icom on Ham community.

      I really wish FCC would just freeze all Dstar sales in US on grounds that its encryption (it is when you cant decode it without their hardware) and not allowed in amateur bands.

      • Mark says:

        Apologies then if i misunderstood your post then sir
        Yes i fully agree that Icom made a blunder. i believe dstar
        should be ignored because of these facts, and any digital
        formats used. i like TDMA – but currently use P25 on Amateur
        -pity Icom’s cynical give away of some dstar equipment just to get its .
        foothold in the doorway was missed, or allowed to go unchallenged
        where better sounding, more resilient, open standard mod schemes
        already exits. such a shame for Ham radio. In the UK there is little
        other digital other than dstar, even dstar repeaters are around, but
        i can not and will not support or use them because of this.
        I wonder if Yaesu’s C4FM will be p25 compatible.

        P25 phase 1 is superb, more resilient,and wastes dstar. the equipment
        is cheaper too. equipment plentiful, decoding easy.
        Dear NON US Hams, seek out P25 transceivers !

  4. DJ says:

    Is there anyone out there who would be willing to walk me through setting up op25 and dsd with sdr#?

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