OP25 OP25 without control channel ?

[hhca]

So i have OP25 running on Pi3. I can navigate to a control channel and see the active talk groups.
I also have used sdrtrunk to monitor this control channel which is very quiet.
I have found a different tower transmitting P25 and i can listen to it with sdrtrunk, i guess part of a different network ? Im not sure what its control tower is, nor can find it, nor may be in range of it. I suspect its operating p25 but without trunking/control. As is rural.

Any idea how i can decode this and eventually get it online ?

Thanks.

 

[boatbod]

So i have OP25 running on Pi3. I can navigate to a control channel and see the active talk groups.
I also have used sdrtrunk to monitor this control channel which is very quiet.
I have found a different tower transmitting P25 and i can listen to it with sdrtrunk, i guess part of a different network ? Im not sure what its control tower is, nor can find it, nor may be in range of it. I suspect its operating p25 but without trunking/control. As is rural.

Any idea how i can decode this and eventually get it online ?

Thanks.

First thing would be to know the frequency of the voice channel. Once you know that you can park op25 on the frequency and see what (if anything) it decodes. Preferably have the logging set to "-v 10" so you can see what NAC is assigned (assumes Phase 1 voice channel) and then do some research on RRDB to try to match the frequency and NAC to a specific system.

Alternatively (and this is hard to do on a Pi3 due to the low power CPU) set the sample width to max (-S 2400000) and turn on the FFT plot (key #1) while you look around for a signal spike that never goes away. Tune to this frequency and see if you manage to pick up a control channel.

 

[hhca]

Thanks for your reply, from listening to it with sdrtrunk i can read its nac and talk group (and freq obviously), the system (nor any p25 in my part of the state (NNSW AU) isnt documented in RRDB)

What im thinking is that there is no control channel, and its just standalone P25 encoding, as the tower transmitting has very limited services on it,, with p2p links to other towers that are out of range of ground units accessing said tower (including me).

What im trying to work out is how to get OP25 to just decode the given frequency to audio, rather than decode it to control messages and then follow a trunking system and .tsv to tune talk groups....

 

[hhca]

update: actually it is documented as P25 Digital PMR New South Wales - NSW Rural Fire Services Scanner Frequencies and Radio Frequency Reference

 

[boatbod]

What im trying to work out is how to get OP25 to just decode the given frequency to audio, rather than decode it to control messages and then follow a trunking system and .tsv to tune talk groups....

That's easy... just use "-f <freq> -V -U" on the rx.py command line and it will decode P25 conventional traffic. Do not add the -T trunk.tsv
Also, don't expect to see much activity in the terminal screen.

 

[hhca]

Hey that works, and on my Pi3 ! Thanks a bunch