how to use P25 phase ii decoding function in dsd+

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AgentSdr

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The recent dsd+ has supported p25 phase ii decoding but i don't know how to use it. As for phase i, the source audio is sent to dsd+ using the NFM demodulated results of sdr# ,but for phase ii how to do it?Do we need a CQPSK demodulator in advance or it can directly demodulate the raw signal ?
 
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simpilo

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Start CC-FMP24.bat, CC.bat, VC-FMP24.bat, VC.bat all 4. no virtual cables used. All tcp linked. no hassle just type in the control frequency in CC-FMP24 window and press Enter.
The recent dsd+ has supported p25 phase ii decoding but i don't know how to use it. As for phase i, the source audio is sent to dsd+ using the NFM demodulated results of sdr# ,but for phase ii how to do it?Do we need a CQPSK demodulator in advance or it can directly demodulate the raw signal ?
 

R0am3r

Salt Water Conch
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Apr 13, 2014
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724
Location
Oneida County, NY
Ok – I’m stumped and can’t seem to spot my error. I trying to monitor the Oneida County, NY P25 Phase II system using DSD+ 2.176 and two RTL-SDRs. Tuner 1 is receiving the Control Channel (151.010 MHz) with FMP24, and DSDPlus appears to be decoding the channel. I can see the TGIDs in the DSD+ window.

Tuner 2 is used for the voice channel. When I start the FMP-VC.bat file to monitor the voice channels, nothing is appears in the second FMP24 window. It doesn't even draw the spectrum display that I see in the control channel window. The app starts, but the FMP24 window is blank and doesn’t appear to see any of the P25 voice channels.

These are my batch files:
FMP-CC.bat: FMP24.exe -i1 -o20001 -P65.0 -f151.010
CC.bat: DSDPlus -fa -rc -i20001 -v3 >>CC.log
FMP-VC.bat: FMP24.exe -i2 -o20002 -P83.0 -rv
VC.bat: DSDPlus -rv -Pwav -i20002 -v3 >>VC.log

I swapped the RTL-SDRs in the batch files and verified both are working as advertised. So what am I doing wrong?
 

R0am3r

Salt Water Conch
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Apr 13, 2014
Messages
724
Location
Oneida County, NY
The immediate issue with the earlier batch file was the lack of a bandwidth filter. Adding the -b9.5 option corrected most of my P25 Phase II reception issues. Since this initial fix, I also discovered that both of my RTL-SDRs were a bit off frequency. So, I tweaked the PPM value for both of them. Yes, putting the RTL-SDRs on the exact frequency of the control channel and the voice channels really does help. I wonder how much these dirt cheap SDRs drift throughout the day?

Here the latest copy of the StartP25PhaseII.bat fie:
Start CMD /c FMP24.exe -rc -i1 -o20001 -P64.0 -f151.010 -b9.5
Start CMD /c DSDPlus -F2 -e -f1 -i20001 -rc
Start CMD /c FMP24.exe -i2 -o20002 -P83.0 -rv -b9.5
Start CMD /c DSDPlus -F1 -f1 -rv -o1 -i20002
 

slicerwizard

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Sep 19, 2002
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7,643
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Toronto, Ontario
The immediate issue with the earlier batch file was the lack of a bandwidth filter. Adding the -b9.5 option corrected most of my P25 Phase II reception issues.
Yep, monitoring a PSK P25 signal with the bandpass filtering set to 7.6 kHz will do that. We need to compile a list of gotchas...

Since this initial fix, I also discovered that both of my RTL-SDRs were a bit off frequency. So, I tweaked the PPM value for both of them. Yes, putting the RTL-SDRs on the exact frequency of the control channel and the voice channels really does help. I wonder how much these dirt cheap SDRs drift throughout the day?
Doesn't matter, since FMP24 auto- fine tunes to match the drifting. I have an Airspy that insists on being off a coupe of kHz, so decoding starts off choppy, but after sitting on a channel for 15 seconds or so, the auto tuning dials it back in. FMPA and FMP24 both do it.
 

R0am3r

Salt Water Conch
Premium Subscriber
Joined
Apr 13, 2014
Messages
724
Location
Oneida County, NY
With the latest Fast Lane release, I moved to a single RTL-SDR configuration. This is the batch file I'm using:

Start CMD /c FMP24.exe -rc -i1 -a1 -o20001 -P23.0 -f151.0100 -b9.3
Start CMD /c "DSDPlus -r1 -e -T -E -i20001 >OneidaCtyP25.txt"

Thanks to all who provide guidance with DSDPlus. I am now officially addicted.
 
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