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How to configure NXDN 4800 trunked network

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#1
How to configure NXDN 4800 trunked network ?

I have a new nxdn 4800 VHF with 4 frequencies . I made a configuration with 2 SDR s :

one aispy with FMPA to monitor control channel
one SDR RTL to monitor voice communications

It is working but I m not sure to need both configuration . It seems that the voice channel is only decoded with scan option of fmp24 batch file .

What is the way to go to the working voice frequency using the airspy batch control channel ?

I m using DSD + fast lane version 2.18
Is their any exemple how to configure properlly ?

Thanks for answer
 
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#2
Basically you need 4 programs running:
FMPA24 for tuning the control channel with TCP output to DSD+ below. Use -rc option.
DSD+ for decoding the control channel with TCP input from above. Use -rc option.
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FMP24 for tuning the voice channels with TCP output to DSD+ below. Use -rv option.
DSD+ for decoding the voice with input from TCP above and output to speakers. Use -rv option.
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Your DSDPlus.frequencies file must contain the 4 channels in the system with channel numbers associated with frequencies. An EXAMPLE follows. Put your own information in for your system.
NEXEDGE48, 69, 2, 074, 453.17500, 0, 0
NEXEDGE48, 69, 2, 118, 453.45000, 0, 0
NEXEDGE48, 69, 2, 168, 453.76250, 0, 0
NEXEDGE48, 69, 2, 238, 460.22500, 0, 0
(system 69, site 2, channel 238, frequency 460.22500, 0,0)
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Determining the channel numbers can be done by various means. Read the threads here if you can't figure it out. You will know the active control channel number just by watching the DSD+ output. If all else fails just write down the channel numbers and use trial and error to match them to the frequencies. I use the -v3 option on the CC copy of DSD+ to get more information when it is running.
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Tune the control channel receiver to the active control channel. It's associated copy of DSD+ will decode the control channel activity and automatically tune the voice channel receiver based on the channel number information in the DSDPlus.frequencies file. Once tuned the copy of DSD+ associated with the voice channel receiver will decode the voice and play it to the speakers.
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All files need to be in the same folder...
Read the trunking.txt file.
 
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#4
You need 2 receivers, one for the control channel and one for the voice channel. The control channel receiver can be anything that will feed audio to DSD+ running in -rc mode. The voice channel receiver must be a RTL-SDR so it can be controlled by FMP24. If both receivers are being controlled by FMP the setup will have the added ability to follow a moving control channel as some NXDN trunked systems move it around.
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Once again, read the trunking.txt file that comes with DSD+...
 
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#5
after reading this post and trunking.txt , I succeed . I still a problem with voice decoding . Signal is strong but nxdn 4800 isn't decoded properlly . It is garbage . I'm using 2 RTL SDR . The RTL for voice is thumbnet V3 . I'm using fmp24 .

I don't undestrand why my BW is changing when I receive my first trunked voice communication

I'm setting BW with like :

FMP24 -i2 -o20002 -b9.5 -g49.8 -f171.65625 -s0 -z0 -rv -v500 so 9.5

on the top display I have the value BW:4 . That should explain the bad decoding result . I don't understand where the BW:4 is coming from

As soon as I have a call in the first windows (Control channel) , the call is assigned throught TCPIP and the fmp24 setting is chanched from BW 7.6 to BW 4 . I configured the fmp24 with BW 12.5 . Very strange
 
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#6
The bandwidth is automatically set to 4 by the NEXEDGE48 in the DSDPlus.frequencies file as 4 is the correct BW for that mode. If the voice is not scrambled your problem may be that you need to calibrate your dongles for frequency correction. See the -P option in FMP.txt file.
 
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#8
It is working fine now . It is one of our ski station in the Alps . I put the exacts frequencies (found with sdrsharp) in dsdplusfrequencies file and I reduce volume option v from 500 to 100 .Working fine

Thanks for help
 
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#9
Great, glad you have it working. Of course the frequencies should in most cases be the standard frequencies in the database. You can use sdrsharp to tune each dongle to the control channel listed frequency and then adjust the PPM value to center the signal. That is a good method to determine the correct PPM setting for each dongle. Once determined, use that in the -P parameter of FMP24. Allow the dongles to run and warm up for about 10 minutes before making the final adjustment in sdrsharp.
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I have found that using dsdtune to tweak the parameters on NXDN also helps with the audio quality. If you get bored you should investigate that program and procedure.
 

garys

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#10
One of the nice things about NXDN is that the data stream transmits the channel numbers for the system. At least I've seen that with DSDPlus. It also transmits the User Alias if it's programmed into the system.

One thing I've noticed is that FMPA-CC reports a BW of 7.6, but channel step size of 6.25. FMP24-VC reports a BW of 4 and channel step size of 6.25.

DSDPlus works very well on NXDN once it's set up properly. Then again it works well on all systems once it's set up properly. :)
 

garys

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#12
Yes, NXDN will transmit the "Alias" of individual users if they are programmed into the system. A tow company I've been listening to uses the drivers names instead of unit numbers. It certainly helps when an alias is "AMB 1" or "BUS17". :D

this nxdnnetwork is also sending radio owners name : funny .
 
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