Help with audio from Unitrunker/DSDPlus P25 Trunked system

[BigE_78660]

New to SDR so any help will be appreciated. I have the system working but my audio is garbled. Not all audio, but there doesn't appear to be a defined pattern to the garbled audio.

Attaching is a jpg of my Unitracker setup. Also below is a link to the .wav file of the audio.

https://1drv.ms/u/s!AIVhiE89earXiBk


Note: I am using Nooelec's NESDR SMART dongles.

 

[jonwienke]

Sounds like decoding garbles from being on the fringe of reception. You're getting some of the digital audio data but not all of it.

 

[BigE_78660]

Thanks for the feedback. I thought I might be needing a better signal so I went out and purchased two radioshack 800Mhz antennas and it didn't make any difference in the performance. I have also been looking at the RSSI value for both dongles and 68 seems to be a fairly strong signal.

 

[SCPD]

To squeeze a little more performance, turn off drift correct, and manually adjust the PPM value by .5 or .25. This should reduce window value a little closer to zero.

 

[SCPD]

I just noticed you have full AGC turned on. Work on getting the signal role VCO's decode rate close to 100%.

Leave base band AGC on but turn tuner AGC off. The trouble with that much AGC is a strong signal appears in the SDR's pass band - which causes the AGC to drop overall gain - which can kill the signal you actually want. I don't know if that's the cause here but is an easy experiment to do.

 

[KevinC]

Moved to the decoding forum for better visibility and support.

 

[BigE_78660]

Unitrunker, thanks for the guidance with regards to the AGC and PPM settings. I made those adjustments and the audio is improved, but I still have about 30% of calls garbled. I will keep trying different adjustments to improve my audio clarity.

A question or two about your last post if I may.

What do I look for in the signal tuner window to determine my % decode? Currently the window on that receiver is continuously above 80.

I have also noticed that the garbled audio seems to correspond to when the window on the voice tuner gets above 20 or 25 is this a good indication of what might need to be tweeked or no correspondence at all?

Thanks

 

[SCPD]

The window value is an indication of how far off-frequency the received signal is to the VCO tuned frequency.

A small window value (close to zero) is good.
A large +'ve or -'ve window value is bad.

Sounds like you need to adjust the warp correction value.

The decode rate appears on the site window and also in the signal role VCO tab as "Health" right next to "Protocol".