1. First we're going to check the device driver is install and working correctly.
Plug the RTL device and in a command window type "lsusb". You should see something that says "Realtek Semiconductor Corp." or similar.
2. Next it's helpful to see if the rtl driver can successfully be opened. I like to use the "osmocom_fft" utility for that. Simply run the command and if a gui window pops up life is good. If the window does not appear, there may be a problem with blacklisting. Close the window before moving on to the next step.
3. Now it's time to try running op25. You'll want at least two terminal sessions open.
In the first terminal window, run the following commands:
cd ~/op25/op25/gr-op25_repeater/apps
./op25.sh
In the second terminal window, run the following commands:
cd ~/op25/op25/gr-op25_repeater/apps
tail -f stderr.2
4. At this point you should have a scrolling log in one terminal and the op25 app in the other. In an ideal world, the op25 screen would have a rolling "tsbks" counter in the top right hand side. More likely the counter will be stuck at 0, which means we need to tweak the tuning to dial in things like PPM error correction and fine tuning.
5. In the op25 screen, press the "1" key and a window should pop up with the FFT plot showing the control channel signal somewhere near the center. Your task is going to be to dial in the ppm error correction (-q parameter in op25.sh) so that the peak coincides with the vertical tuning line. Use positive or negative values of "-q ##" to make the correction in the startup script file op25.sh.
6. When the tuning is close, you can make fine adjustments using the ',' and '.' keys in the op25 window. There's a bit of a lag, but you should see the number in parenthesis (after "frequency") go up or down by +/-100. Typically if PPM is correct, you'll not need more than about +/- 350 fine tune. You can switch to plot "5" (mixer) to more accurately make the fine tuning adjustments. The goal is a symmetrical hump with closest to 0 "Mixer: balance" shown at the top of the plot screen.
7. At this point you should have a rolling tsbk counter and hopefully be receiving audio. If not, let me know what's going on with screen shots and copies of the stderr.2 log and I will try to help further.