DSDPlus 1p101 Trunking Help

[R0am3r]

What does everyone do about the lack of frequency accuracy for the RTL-SDRs for trunked systems? For the NXDN system that I am attempting to follow, I have found that my RTL-SDRs are off frequency by quite a bit and I have to modify the values in the DSDPlus.frequencies file. This ends up as a guessing game to accurately make the SDR land on the right spot for proper decoding of a trunked voice channel. When I see a channel become active, I have to look at the waveform in the spectrum to see how much to modify the values in the DSDPlus.frequencies file. I do this until I get it right.

Here is an example of the inaccuracies in the system:

ACTUAL OFFSET NEW
453.1875 (CC) .0295 453.15800 Control Channel
453.5000 (2) .0375 453.46250 *works!
460.1125 (3) .0400 460.07250 *works!
460.3875 (4) .0525 460.33500 No luck yet
460.4625 (5) .0525 460.41000 No luck yet

Sorry, the formatting doesn't work too well.

 

[Forts]

I suspect you are manually adjusting the frequencies and not setting the proper PPM value? Leave the frequencies set to what they are supposed to be and play with the PPM adjustment value. For example one of my dongles needs a value of -20, whereas another is about +10. It will vary from dongle to dongle and will vary until the dongle heats up. Once it's been running 10 or 15 minutes the PPM value will stabilize.

 

[dave3825]

If you mean frequency drift, you adjust the frequency correction (ppm), not the frequencies.

Here is a video showing how to do it. Just make sure you tune to a good known frequency https://www.youtube.com/watch?v=63cd6_UHprI

One of my sticks is off by 77 ppm and the other by 42 ppm. I labeled each stick with the ppm value.

After you determine your drift and mark the dongle, and fmp is running, you use capitol C and lowercase c to adjust the drift. One makes the value go up, the other makes it go down. Set it to what was best in sdsharp. On the top right of the fmp window, you should see "corr 0.0". The number you get from sdsharp would be to the left of the decimal. Mine reads 77.0

No guessing involved



.

 

[R0am3r]

Forts & dave3825 - Thank you!!! Your directions for entering the frequency correction (PPM) were perfect. I used SDRSharp on a known frequency (the control channel) and then adjusted each RTL stick until it was centered on the waveform. One stick was 63 and the other was 83. I then modified the FMP batch files with these values and also returned the DSDPlus.frequencies file to the correct frequencies. I fired it up and I am now decoding audio on all of the voice channels. The system works perfectly!

 

[Digitalarms]

For the life is me DSD Plus just will not start decoding!

Stops at mono decoding just don't get the decoding stream up after that like you see on line. Every things scrambled using Audio virtual cable. Take a look at my screen shot. There isn't any support anywhere that I could find on how to enable decoding with DSD. Tryed -fa but the only thing it did was forget settings please lost!