OP25 Can't obtain NAC for target frequency ...

[akwusmc]

All,

Trying to get OP25 up and running. I'm following the tutorial by John Hagensieker, but after I run the first script mentioned and substituting the target frequency (./rx.py --args 'rtl' -N 'LNA:47' -S 2500000 -x 2 -f 151.0325e6 -o 17e3 -q 2) as well as removing '-q 2', all I get (for both) is:

Allocating 15 zero-copy buffersdefault, Jul 28 2020, 12:59:40)
[GCC 9.3.0]



Frequency 151.032500(0)

By poking around, I note that op25.sh is basically the same rx.py script but pulls the frequency from the trunk.tsv file. The default frequency gives:

NAC 0x0 WACN 0x-1 SYSID 0x-1 0.000000/0.000000 tsbks 0

Changing the frequency in trunk.tsv to my target frequency returns the same thing (the same NAC).


AFAIK, I can go no further until I can determine the NAC for the target frequency. If there's something I'm not doing that I should be or doing something wrong, I'd appreciate someone steering me true!

TIA

a

OS Linux Mint 20, 'Cinnamon desktop

 

[boatbod]

If you are monitoring trunked P25 you don't actually need to know the NAC because 0x0 will let the app lock on to the first nac that it sees.
Likely a bigger issue is that op25 isn't tuned correctly. What do you see in the fft plot (#1) and datascope plot (#4)?

 

[akwusmc]

Invoking op25.sh ...

fft plot



datascope



I'll admit that the antenna I've got on my SDR is not optimal (cheap rabbit ears) by any means (when county dispatch was on analog FM I used my 2m antenna) so I'm sure I'll need to get that sorted out as well, not to mention it's a small county and not much going on traffic-wise.

a

 

[nick0909]

From that first plot you basically have no signal. If you are really using LNA:47 for gain you have that already turned up pretty high. I would suggest trying a better antenna or location, you need a much bigger bump of signal on that first plot.
Don't use the -q or -d fine tuning until you know what is needed for your device, every device is different.

 

[boatbod]

From that first plot you basically have no signal. If you are really using LNA:47 for gain you have that already turned up pretty high. I would suggest trying a better antenna or location, you need a much bigger bump of signal on that first plot.
Don't use the -q or -d fine tuning until you know what is needed for your device, every device is different.

Yup it looks like you hit the nail on the head; there is insufficient signal, so nothing to tune.

 

[akwusmc]

Appreciate the help ... I knew the antenna was suboptimal, so I'll see about improving!

a