Since I have a radio capable of transmitting Digitally using the Project 25 protocol. I wanted to test it out. The only issue is that there are no P25 ham radio repeaters in receiving distance from my house and I do not have another P25 radio to communicate with. After searching around Google, I found some websites discussing software that will decode the digital signal and convert it to analog over your computer’s sound card.

Hardware Needed:
Scanner – I guess it can be any kind as long as you can get at the discriminator output. I used a Radio Shack PRO-97.
Audio Patch cable – From the discriminator output to the computer
Computer – Not sure what the minimum requirements are. I used a 1.5Ghz single core AMD (Circa 2003) and a motherboard with a built-in sound card.
Sound Card (If you computer doesn’t have Sound Card) – I don’t think there is a need to go out and spend hundreds on a card that your going to use for this purpose. The money spent on a expensive card could have been spent on a scanner that can decode APCO25. I’ve found that a sound card using the AC97 Codec works the best.

Software Needed:
Linux OS Or Windows – That’s right L-I-N-U-X!! DSD Will NOT run on ANY KIND OF WINDOWS OS. Let me type that again. DSD DOES NOT RUN ON WINDOWS!!!  Sorry but I had to do that.  I’ve used UBUNTU Ver 10.04 . At the time of writing this, the current version of Ubuntu is 11.04 . For some reason DSD DOES NOT WORK WITH UBUNTU VERSION 11.04 . The reason I choose Ubuntu is that it’s downloadable,  free and has a Graphic user Interface. Since I never Ran Linux before, I felt a little more at home with Ubuntu. You can run a Dual Boot system so that when you start the computer, you can have a choice of which Operating system to boot into. With Ubuntu you can also run Ubuntu off the CD instead of installing the OS on the computer.  Please note that there is a lot of reading in installing Ubuntu which I will not cover on this website. Google questions you have and I’m sure there is an answer out there

DSD (Digital Signal Decoder) – This is the software that actually takes the digital signal and decodes it.
Mbelib – This software actually takes the decoded information and synthesizes it so you can hear the decoded audio.

DSD and mbelib can be downloaded from here (See note at the end of this writeup)

After modifying your scanner and getting Linux to run, download Mbelib and DSD in Linux and remember where they are located. In terminal CD (Navigate) to the directory where both Mbelib and DSD are located, Unpack both Mbelib and DSD and then install Mbelib first then DSD. If your very new to Linux and have some computer skills, this thread helped me out.

After installing everything, in Terminal type “dsd” (without quotes) and If all goes well. The last line should be “Audio In/Out Device:  dev/audio”
Errors that I got at this point mostly have to do with sound.  Either your sound card is being used by another application (even the sound control panel) or DSD is not calling up the correct sound card. DSD is defaulted to use sound card device 0 (zero). So if your sound card device is in a different spot then you need to tell DSD the location for the sound card. You can check where your soundcard is (if it’s installed) by typing “aplay -l ” into terminal. If it’s device 2 for example then you type in terminal “dsd -i /dev/audio2 -0 /dev/audio2”

I’ve uploaded a video showing up how DSD works with APCO 25 (P25, Project 25). It also works on other digital modes but I have not yet tried.

I am loving this software. It’s not the easiest software to install or use but if your into scanning and just even wondered about Linux. This is the perfect project to get your feet wet in Linux.

Please note that I am not an expert on the DSD software or Linux. Most likely I will NOT be able to help you if you’re experiencing problems. The install went so great for me and worked so well that I wanted to install it on another computer. After installing it on another computer, I had nothing but trouble. The good that came out of having a hard installation is that I learned a bit about DSD and Linux.

Thanks for reading

UPDATES 10/24/2011
I haven’t been using DSD much as I’ve been out of touch with APCO but I was informed by a user on Youtube that There is a verison that runs in windows.

Here is the link to the RadioReference Thread

Basically what the Author did was compile all the stuff from the linux version of DSD into a windows .exe file.  If you just want to listen to P25, Download the version in the 3rd post of the thread. All you have to do is un-zip everything into a folder and run dsd.exe

I’ve tested it against my XTS3000 (P25) and everything looks and ran great. I think the Audio was a little better sounding on my Linux box but the audio is still legible and I’m glad to now have it on a windows box. Maybe I’ll listen to it more often.

Make sure to plug into the discriminator tap and put the other side into the LINE-IN (Blue). Before loading DSD make sure that the LINE-IN is your DEFAULT recording device and you should be all set. If you try to do this while the DSD is running you can run into issues just like when it was in Linux.

Thanks to the RR crew because it makes scanning more fun and less expensive.