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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 02-21-2012, 3:32 PM
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Default DSD on simulcast P25 systems

Hi gang,

OK, for fun and because I had a three day weekend this past weekend (neener neener) I decided to see if I could get my ancient BC895 with a discriminator tap up and running using the wonderful windows port of DSD. I'm pleased to report that my initial tinkerings resulted in a good degree of success! The program recognized the incoming signal and after adjustng my microphone input to a VERY low number, syllables, beeps and sometimes even actual voice comm's from our two scanner unfriendly digital simulcast systems could be heard from my laptop's tiny speakers, thereby turning my old analog dinosaur 895 into an (albeit crude and for the most part unreliable) conventional digital scanner. That, in a word or two, IS VERY COOL! Hats off to the DSD folks who made this all possible.

Now I'm looking for tips and tricks from hopefully another brave soul who has also attempted this sort of thing that could help improve the reception/decode rate. Right now I see lots of low %'s coming up in DSD, 2%, 3% sometimes I'll get really lucky and see 10% but regardless of that, for the most part the audio quality is quite low. I'm also running this on a very cheap laptop with no doubt a bargain basement sound card, so I'm also open to hardware suggestions also.

Here's what I have:
A discriminator tapped 895
DSD and Unitrunker
A control cable for the 895 (uhhh... somewhere...)
A RCA to 1/8" mono patch cord
An old unused WinXP machine that should run DSD and Unitrunker with no issues.

Here's what I need to know guys:
What soundcards should I get? Which ones give the best results?
What command line options seem to work the best on these systems? After some tinkering I found that the only command line option that seemed to help was -mq which limited the optimization to CQPSK only and even that was neglible.
I think the biggest source of my problem is the quality of the tap itself. It was done YEARS ago and it's just a straight tap, no capacitor or any of that. I'm thinking of redoing it and adding the capacitor - would that help at all?
Tips on Unitrunker - is it possible to run it on just one scanner and have it hop to the voice channels on it's own? Skip talkgroups I don't want to stop on? Etc? I think it's possible but I'm not sure. I know DSD has options for scanner control also but knowing Windows, only one program can grab the comm port at a time so Unitrunker will need to be able to find it's way back to the control channel on it's own.

Thanks for the tips and tricks guys... I'm enjoying having a "second" digital scanner to play with.

-AZ
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Old 02-23-2012, 11:35 AM
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Well shoot, I can't be the only guy crazy enough to try something like this... let's simplify: Anyone who has successfully set up a monitoring station with Unitrunker and DSD care to chime in and offer tips/advice? I'll be redoing my discriminator tap to include a 10k resistor as recommended in Scott's excellent how-to document this weekend. Any other ideas/suggestions?

Thanks,
-AZ
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Old 02-23-2012, 10:51 PM
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You didn't mention what the specs of your PC were (namely processor). I don't care what anybody says, DSD is quite the CPU hog. On my my Core 2 Duo T5750 laptop, CPU maxes out when decoding digital -- and that hampers my ability to fully determine what else I can improve. The maxing CPU is enough to lessen my decode quality.

I've always used a tap with a 10k resistor, so that's the only way I could recommend doing it.

Optimizations in DSD never seemed to make a difference, regardless of the digital signal I was trying to decode.

Mike
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Old 02-23-2012, 10:54 PM
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Quote:
Originally Posted by AZScanner View Post
Tips on Unitrunker - is it possible to run it on just one scanner and have it hop to the voice channels on it's own?
No, Unitrunker is designed for full time monitoring of the control channel. You'll need separate receivers for voice and signal roles.

For a controlled receiver feeding DSD, check P25 box in the Unitrunker receiver window so the program knows it's okay to steer the analog radio to P25 voice calls.

Last edited by Unitrunker; 02-23-2012 at 10:57 PM..
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Old 02-23-2012, 11:03 PM
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I've done something similar, only with the Windows Unitrunker, Linux version of DSD, and two Maxtracs:

MaxTrac Arduino brain transplant?

Good fun, but a bit unwieldy, with some delay and poor voice quality. But hey, as a proof of concept, I'm calling it a win.
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Old 02-27-2012, 1:16 PM
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Quote:
Originally Posted by Unitrunker View Post
No, Unitrunker is designed for full time monitoring of the control channel. You'll need separate receivers for voice and signal roles.
Awww... that's a bummer. I was hoping to turn my BC895 into a full fledged digital scanner like my BC796D. That would have been quite the conversation piece. Oh well, using it to actually decode live digital voice data is about the neatest darn thing I've ever done with it. Thanks for the info!

-AZ
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Old 03-10-2012, 8:41 PM
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Default AZScanner

To use your 795 as a digital scanner, get another scanner to listen to the CC (like an old BC7 or any old scanner that does the band you want), then let UT control the 795 with the digital mode checked in UT. So then your 795 is a digital scanner.

I think that is what UT author Unitrunker was trying to say.
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Old 03-16-2012, 4:05 PM
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Quote:
Originally Posted by jets1961 View Post
To use your 795 as a digital scanner, get another scanner to listen to the CC (like an old BC7 or any old scanner that does the band you want), then let UT control the 795 with the digital mode checked in UT. So then your 795 is a digital scanner.

I think that is what UT author Unitrunker was trying to say.
Oh I know. But I was looking for something that would allow me to use just one scanner to accomplish what my 796 can do. I'm exploring a few "out of the box" options that might work, including writing a small app that would simply watch DSD do its thing and resume scanning if the app detected a talkgroup was encrypted or not one I wanted to monitor - similar to how you'd conventionally scan the system on a programmed Motorola radio and tell it to only stop on talkgroups such and such. I could include it in the DSD source code but I don't want to have to recompile everytime something new is added to DSD. I'd rather keep the two seperate so I can just copy over the new DSD binary and go.

-AZ
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