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Digital Voice Decoding Software For discussion of software applications which decode digital voice formats such as P25, NXDN, MotoTRBO, etc. Please use the HF Digital Signals forum for anything below 30MHz.

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Old 01-31-2013, 1:36 PM
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Hi all,

I've been messing with DSD for the past few months and I think I know enough about it to be dangerous. I do know that my current set up which consists of a 3 year old laptop and a 15 year old scanner isn't gonna cut it. I want to go ahead and take the plunge and set up a dedicated Unitrunker/DSD monitoring station using a desktop PC and 2 SDR dongles. Rather than attempt to reinvent this wheel, I thought a good first step would be to seek the advice of fellow seasoned DSD'ers because when I start trying to research things like SDRSharp and GNU radio my eyes gloss over and my brain screams "where's the 'easy' button?"

First off, what is the best SDR dongle to get? Ideally I want this dedicated system to have two of them, one for control channel monitoring and then another for voice comm's which will be decoded with DSD. Is Unitrunker capable of passing voice channel assignments to a second SDR or will I need to write some sort of go-between that can review a log file from Unitrunker and then tune the second SDR? If you happen to have a good source to get these from that isn't ebay (ebay hates my credit card for some unfathomable reason) I could use that also.

Secondly what are the minimum specs that I should be looking for when shopping for the PC itself? I currently have a couple of old AMD boxes kicking around, but I will need to add RAM and a hard drive and all that fun stuff. If the older machine isn't up to snuff, then no sense in spending money on additional hardware for it when a new PC is a better answer. So if someone could pass along the specs they are using that'd be a great start for me.

I also will be using Windows 7 to run this machine. In addition to needing Windows for Unitrunker, I'm not interested in building a linux box because I'm a windows guy and will likely be writing some of my own software that will run in the background and sit over top of DSD and Unitrunker so I can do cool stuff like send alpha tags to an LCD display installed on the front panel and fun things like that. I may also at some point get real ambitious and use the P25 processing code in DSD as a template for an RD/LAP decoder since I've always wanted to do that and there's now some interesting GNURadio code floating around out there in cyberspace that contains the gory details on how to process those bits once you get them separated out into 1's and 0's (more like +3's, +1's, -1's and -3's but I digress). Perhaps someone else who is better versed in C would like to have a gander at the code I found - PM me if so because if you can write it better than I can, I'm not above asking for help.

As I go along of course I will be happy to update this thread with progress and pics of my new toy so that other like minds can build one too if they like. So with that said, I'm officially kicking off this project and I welcome any and all tips, advice and comments.

Thank you,
-AZ
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Old 01-31-2013, 6:21 PM
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Hmmm, no takers yet huh? Well that's OK. Maybe I'm the first to come up with such a hair-brained idea.

I've started researching hardware, namely the LCD display I want to use in the PC case to display frequency and talkgroup information just like a "real" scanner would. I found this one which I really, really like:

Newegg.com - nMEDIAPC Black Aluminum Panel PRO-LCD-B Media Center Programmable LCD

but the one thing I'm not seeing is a serial protocol or other means with which to communicate with the thing. It can tell me all sorts of neat stuff like how hot my CPU is or what song I'm playing in media player but I don't need all of that. I just want to be able to send 2 lines of custom text to it.

Is there something like this that is programmable/controllable via a serial interface? I've looked around but I haven't seen anything that looks this uber cool and does what I want. I suppose I could get one and play around with it, but I don't like dealing with returning stuff if it doesn't do what I want. Maybe someone here has bought one of these (or something like it) and can chime in.

Thanks,
-AZ
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Old 01-31-2013, 7:20 PM
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Hi Phil;

There are some decent resources out there for getting programs like SDR#, DSD and Unitrunker to play together. Look at the links in the Unitrunker community page, the SDR# group, and the SDR Receivers section of this forum.
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Old 01-31-2013, 10:11 PM
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Rick (Unitrunker) mentioned SDR# -- It is an extremely efficient / lite program when it comes to CPU usage. It's impressive. I am also testing out v2.sdr-radio.com. What a beautiful interface in the latest SDR-Radio that is being worked on. Both are working fine with my Funcube Dongle Pro / Pro+ and my two DVB-T dongles. Software Defined Radio and Technology previews, just something for the weekend... are the respective links.

I think the first, and biggest, concern should be that you get a multi-core hyperthreading machine. The SDR programs will make use of it; DSD / DMRDecode may make use of one or both of those features. And, if you want to use the machine to run SDR# and DSD and DMRDecode and be able to go about doing anything else you want [work/play] on it, you don't want to get a Celeron.

Once you resign yourself to getting a stout machine, the fun you can have with a sub-$25 dollar dongle is just amazing.

Mike
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Old 02-01-2013, 5:21 PM
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Been doing alot of reading today. I've settled on the ITX form factor case for the PC, but little else. I can envision what this thing will look like in my mind, but piecing it all together is going to take some time. Picture a black ITX form factor case with a blue backlit LCD panel and two small black whip antennae sticking up out of the back. It's gonna look freaking sweet, like something that would be more at home in some NSA lab than on my bookshelf.

I'm also going to be adding an Apache web server to it so I can build a PHP based remote interface that will allow me to program it and control it from any PC (or device with a webbrowser) in the house. It will also have an icecast/oddcast server in it so I can stream audio to other devices on my network and maybe, if it works well enough, to RR also.

My hope is to keep the cost below $300 but being that it's my first one (eventually I want two, one for PD comms and one for Fire/Misc), I'm liable to go a bit over budget, possibly even spending as much as I would on a Uniden or GRE digital scanner, but this radio/pc will be capable of SO much more than today's scanners can do. I'm really looking forward to getting this put together.

Found a great tutorial here on how to get SDR Sharp, DSD and Unitrunker all playing nicely together. Worth a look for anyone else considering such a project.

More to come...
-AZ
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Old 02-08-2013, 4:11 PM
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Hi gang, an update - I ordered two of the Nooelec dongles for this project today (had to wait for a payday where there'd be a bit of money left after the bills got paid) and a buddy of mine has a spare machine he's willing to lend for the project. Hopefully I'll be up and running by early next week and then I'll be able to start posting up some pics of the Frankenscanner as I've come to call it.

-AZ
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Old 02-11-2013, 3:26 PM
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Some new news on this project that may prove helpful to others. While I await the arrival of my new SDR dongles, I spent the better part of an evening this weekend tweaking the settings on DSD. The system I monitor is a CQPSK digital simulcast system and the scanner I'm using for the discriminator tap is an ancient BC895. In addition, the laptop I'm using is several years old and quite underpowered for the task. That being said, I got very good results - almost as good as a "real" digital scanner - by using -mc, -q, -u2 and -A6 command line options for DSD. So if you need to squeeze a little more performance out of DSD, try the settings above. I also found that for this particular system and scanning setup, DSD version 1.51 provided the best results. Can't wait for the new RTL SDR's to arrive (they ship today) so I can try it out on them.

-AZ
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Old 02-25-2013, 11:46 PM
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I'm a getting into this thread a bit late, but it seems to me you would need VAC (virtual audio cable) to feed a SDR to the unitrunker or that windows DSD.

FWIW, I've been using the Rafael Micro R820TRealtek RTL2832U combo mostly under linux (various flavors). I have run it a little under windows, but if you want to run something 24&7, linux would be the way to go.

Most of these older decoder programs were set up for soundcards. When you use a SDR dongle, at least under linux, the sound pops out of stdout. On my list of things to learn is how to set up virtual devices on linux. That is, you can take the audio out of the SDR and make it look like it is coming from a soundcard with a virtual device. I thought you could do this with "jack", but apparently not. Now with DSD, since we have source, it may be possible to do a slight modification and make it accept a piped input

For mode-s decoding, these dongles are great. For radio use, I find sometimes you ask for one frequency, and you get something not exactly like what you wanted, but off just a bit.

Also on the list is to replace the MCX connector on the SDR with a SMA. I just got the parts, so that should be done in a day or two. The MCX connector is not SMD though it is small, so with a magnifier, the jack should be replaceable.

I've run 4 dongles at a time using a USB hub. I got a cheap hub at Frys just to see if it would work at all. The power supply it comes with is only 1A, so I guess the RTLs don't use the full 0.5A from the port. But I will get around to either ordering a hub designed for full power at all ports. I can of course just put a 5V bench supply on the Fry's hub, but probably a hub that is set up for 0.5A per port has (hopefully) better thermal characteristics. Hubs are pretty such OS agnostic.
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Old 02-28-2013, 5:33 PM
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Quote:
Originally Posted by gariac View Post
Most of these older decoder programs were set up for soundcards. When you use a SDR dongle, at least under linux, the sound pops out of stdout. On my list of things to learn is how to set up virtual devices on linux. That is, you can take the audio out of the SDR and make it look like it is coming from a soundcard with a virtual device. I thought you could do this with "jack", but apparently not. Now with DSD, since we have source, it may be possible to do a slight modification and make it accept a piped input
This would be ideal if DSD could work this way - I've been experimenting around with RTL_FM which is a small lightweight command line utility that allows you to tune a frequency and pipe the data to a program like SoX which can then output the raw audio out the soundcard. I tried fiddling around with a way to make SoX "record" the data instead of "play" it but I can't seem to do it without telling it I want the data recorded to a file. The only way that seemed to work was to use the Stereo Mixer as my default input device and then DSD would sort-of pick it up, but of course having the voice and raw audio mixed together made decoding pretty much unreliable.

To update everyone on the status of the project, I have the dongles but not the new computer yet - maybe closer to summer when I'll have a bit more funds to play with hopefully. Until then, I'm going to play with the software side of things and see if I can write my own software to act as the intermediary between Unitrunker and DSD, that way instead of having to run two separate instances of SDRSharp, I can run just one instance of my program instead. Going to be using SDRSharp and ADSB# sources as reference material for a small, simple program that will read data from Unitrunker's debug file, tune a second dongle to the voice channel and then output to an audio device for DSD to pick up. Should be fun.

-AZ
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