VB-Cable Lite is standalone free version of VB-Cable. It's limited to 1 virtual cable. The very mention of VB-Audio brought up bad memories of my experience. You will be better off removing VB-audio if you find that VB-Audio is the culprit. I have to mention changing settings doesn't work. If there is a problem with VB-Audio just remove it and replace it with VB-Cable Lite. I never recommend having a faulty outdated virtual cable anything installed with a newer up to date virtual cable anything.
DSDPlus Request help optimizing P25 voice decoding
- Thread starter trossman
- Start date
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The fact that you are using a VB Cable/ VAC might be your trouble. Have you tried dropping SDR# and the VAC and using FMPx like the DSD+ devs prefer?
I had success today using FMP with DSD+ on the stronger P25 voice channels (SNR ~50 dB). Very few if any errors reported in the DSD logs. Still having a hard time decoding voice from the weaker ones (SNR ~20 dB). With VB Cable out of the equation (audio is transferred internally via a arbitrarily picked TCP port 20002), I'm starting to think the issue is RF related, or something more esoteric in my config.
For any fellow newbs reading this, here are my command lines for DSD+ and FMP, which can be used to make a batch file if desired. I also got the FMP scanlist to work, which is neat (wish it was faster though).
FMP.EXE -o20002 -i1 -g14 -f860.7625 -b12.5
dsdplus.exe -v4 -O NUL -I0 -i20002 -o1 -g100 -u3 -dr0 -dh0 -ds64 -dd10 -dv20 -M15 -f1 -mp -rv
slicerwizard
Member
Your issue is due to the fact that DSD+ 1.101 doesn't handle PSK signals all that well; the -mp flag only does so much. The Fast Lane versions do a considerably better job. And no caps or chokes required.
slicerwizard
Member
So you'd blindly put caps and/or chokes across what, USB power lines? USB data lines? - to suppress "noise" that you haven't measured, haven't established actually exists, haven't established is actually causing *any* signal degradation or decoding errors - and you think you're helping the OP??
I'm not putting my iron near my RTL : ) While cheap and entry level, it has brought me so many hours of joy. With that said, I'm open to anything that won't risk damaging my radio. I am considering throwing a few bucks at the fastlane DSD version for the improved decoding, as well.
And this conversation thread has been very helpful - I've already been able to reliably decode a handful of networks in my metropolitan area. Thanks all.
My next challenge is to try and decode AVL (Automatic Vehicle Location) signal I'm seeing on the P25 network. Might start a new thread if I can't find any info on it. Any experience while I have a captive audience?
Happy new year all. I'll be spending it listening to police dispatches to local drunks.
And this conversation thread has been very helpful - I've already been able to reliably decode a handful of networks in my metropolitan area. Thanks all.
My next challenge is to try and decode AVL (Automatic Vehicle Location) signal I'm seeing on the P25 network. Might start a new thread if I can't find any info on it. Any experience while I have a captive audience?
Happy new year all. I'll be spending it listening to police dispatches to local drunks.
No, not blindly; I keep at least one eye open all the time. The techniques I mentioned are time-honored, proven techniques.
slicerwizard
Member
What exactly are you seeing? Got a screen shot?
Sure thing, screenshot attached. I can also provide a baseband recording if it helps. I have guilty knowledge that its likely AVL (which I'd never heard of until today, if I'm being honest) from an online document which happened to describe this specific Motorola Astro network in my area.
Thanks for everything slicerwizard.
slicerwizard
Member
Sure, let's see a recording of what you suspect is AVL data.
Thanks, here's a link to the IQ wav file (32 bit sampling, 2s recording) in a 7zip archive. If that doesn't work, just let me know. Signal of interest is at 489.0875, as shown in the screenshot.
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To follow-up: Offhand, didn't find anything to decode AVL specifically. But from what I read, AVL uses something called TAIP (Trimble ASCII Interface Protocol), which is basically a serial transfer of GPS points along with some kind of radio/unit identifier, and other status info. I don't have the programming chops to know how to extract raw digital information out of the signal, though. Looks like someone much smarter had some luck pulling it out though (page 32):
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