SDR - Universal Trunker + DSD - AFRN

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kk4lts

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As of today (June 28, 2019), I am finding that most local municipalities have moved to AFRN.

On the old JeffCo Pub Services P25 system, I have no problem with my set up. I usually monitor 855.6875 for the control channel in unitrunker, and I route the output from to DSD+ for decoding the audio. It still works like a champ, but there's not much traffic left on JeffCo.

I've tried to switch to AFRN by changing my control channel to 857.53750. I am able to decode all the P25 traffic (calls, joins, logouts, etc.), but DSD+ isn't decoding any audio. I keep getting messages about "FM Demodulated Signal Detected." See attachment.

Is anyone monitoring AFRN with SDRs? I realize that some of the traffic is encrypted, but it doesn't look like _all_ of it is.

Thanks!
 

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slicerwizard

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You're using Unitrunker plus DSD+ Fast Lane to monitor a P25 site that uses phase shifted modulation; the FM demodulation that Unitrunker uses is not really compatible with PSK. If you're using one or more SDR dongles, all you need to do is run a single instance of DSD+ (running in -r1 [single receiver] mode) and FMP24 (initially tuned to the control channel frequency); that should produce much better results. You get there by running the 1R.bat and FMP24-CC.bat files that come with DSD+ Fast Lane and then manually tune FMP24 to the CC frequency. Done and done.
 

kk4lts

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Thank you for this! This got me going down the right path.

I'm now running an all-DSDPlus/FMP24 setup (no Unitrunker) and am decoding AFRN perfectly. I ended going with the older 4 instances setup (1 FMP24 CC, 1 DSDPlus CC, 1 FMP24 VC, 1 DSDPLus VC) instead of the single receiver mode, but that is good enough for now. I'm not sure I understand how single receiver works with two SDRs.

Anyway, now I need to set up labels for talk groups. I really like this setup.
 

Jtolar

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I did the opposite a while back. I stopped using DSD and let Unitrunker handle the decoding. The only issue I have seen is that if it is a weak signal (under 50 health) it won't decode but I have a strong enough signal it's not an issue.

1562179101239.png
 

Jtolar

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The Unitrunker Google Group. Google Groups you will have to request membership but they (the developer) is really responsive and active. They are working on a new 2.1.x version but it is early beta and doesn't work yet.
 
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