DSD+ Decoding of P25 P2 System - Meaning of DSD+ Message

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rkillins

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Hi folks,

I am using DSD+ (fastlane) V2.46 to monitor a new P25P2 system here.

I am seeing this message in the CC Event Log. I suspect it's not good and may be interfering with the success of my monitoring.
Is anyone able to tell me what this means and what I should do to eliminate this error (?) and optimize the accuracy of my decoding?

FM demodulated PSK signal detected
Use TCP linked FMPA/FMPP/FMP24 and correct channel bandwidthto decode.

I am using FMP24-CC for the control channel and FMP24-VC to monitor voice. Two RTL-SDR dongles.
 

mtindor

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Hi folks,

I am using DSD+ (fastlane) V2.46 to monitor a new P25P2 system here.

I am seeing this message in the CC Event Log. I suspect it's not good and may be interfering with the success of my monitoring.
Is anyone able to tell me what this means and what I should do to eliminate this error (?) and optimize the accuracy of my decoding?

FM demodulated PSK signal detected
Use TCP linked FMPA/FMPP/FMP24 and correct channel bandwidthto decode.

I am using FMP24-CC for the control channel and FMP24-VC to monitor voice. Two RTL-SDR dongles.
you only need fmp24-cc and DSDPlus. you only need one dongle, one instance of FMP24 and one instance of DSDPlus. And the FMP24 and DSDPlus must be TCP-linked together to support PSK. If you are using virtual audio cables, that is not going to work. And if you are monitoring a P25 PSK signal, you'll want to switch bandwidth "b" in FMP24 to 12.5 khz.

Mike
 

rkillins

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Thank you Mike. Just getting used to DSD+ and this is the first/only P25P2 system in the area, so it's a considerable learning curve. I'm used to one dongle to decode the CC channel running FMP24 (CC) and the other running FMP24 (VC) to listen to the voice. I don't use virtual cables (honestly don't even really know much about their use).

And, I'm unsure what a PSK signal is. Is it voice, or data. Would I be missing anything if I wasn't decoding a PSK signal. How do I tcp link together, and will it impact the success of listening in on voice transmissions.

Sorry, if these are advanced discussions and out of the realm of the novice. Just trying to discover this new system.
 

mtindor

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PSK / LSM / CQPSK / *PSK - when you see them talked about here, it means a simulcast P25 site. So the site you are monitoring is a P25 Simulcast. DSDplus can tell that, and it knows that if you aren't running FMP24 TCP-linked to DSDPlus, that it can't reliably decode it.

Try just using one dongle, FMP24-CC, and one copy of DSDPlus.

And in FMP24, when you are in the waterfall screen, press "b" until you see the bandwidth at the top of the waterfall screen say 12.5.

And in DSDPlus, in the Event Window, use the menu system
- input --> USE TCP LINKING
- CONTROL --> COMBINED CC/VC MONITOR

And assuming you have things set up in your FMP24-CC and DSDPlus so that the correct TCP port is referenced in the batch file for each one, you should be good to go.

I use:

FMP24-CC.bat
=========
FMP24 -i1 -o20001 -f935.0

1R.bat
=====
DSDPlus -r1 -e -T -E -Pwav -i20001 >>1R-log.txt

The key things here are that -i#### in the DSDPlus batch file and the -o##### line in the FMP24-CC.bat should reference the same TCP port (in my case 20001). And the first time you do this, your firewall may throw up a warning (and you'll want to acknowledge that you do want to open the ports for use)

mike
 

rkillins

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Hey Mike, thanks for the run down. I was expecting it to be far more complicated. I'll be sure to give it a go tomorrow when the system might be a bit more alive.
 

slicerwizard

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PSK isn't only used for simulcast. Any P25p2 system will likely use PSK modulation.


DSD+ is complaining because FMP24 isn't using an appropriate channel bandwidth. Just fix that. Easy peasy.

FM demodulated PSK signal detected
Use TCP linked FMPA/FMPP/FMP24 and correct channel bandwidth to decode.
 

mtindor

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PSK isn't only used for simulcast. Any P25p2 system will likely use PSK modulation.


DSD+ is complaining because FMP24 isn't using an appropriate channel bandwidth. Just fix that. Easy peasy.

FM demodulated PSK signal detected
Use TCP linked FMPA/FMPP/FMP24 and correct channel bandwidth to decode.
I knew that, just forgot. I think you purposefully sit back and wait for somebody else to respond so that you can correct them :)

m
 

KA1RBI

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Any P25p2 system will likely use PSK modulation.
This requires a bit of elaboration. P25P2 is likely PSK on the voice channels. However this doesn't necessarily always apply to the control channel. That is, we've seen an occasional odd P25P2 system or two here or there that utilize "conventional" FSK4/C4FM on the control channel, as confirmed by eye pattern diagrams...

73

Max
 
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