Unitrunker not decoding P25

[tbiggums]

Now that I got Unitrunker working on my newer PC, I'm trying to use an older desktop PC that I can leave dedicated to Unitrunker. It's a Dell Demension 3000 with a 2.4 GHz Celeron CPU running Win XP SP3 Home with 512 MB of RAM. I'm trying to use discriminator audio into the built-in LINE IN jack (SoundMAX Integrated Digital Audio).

The waveform looks pretty good to me (see below), but it won't decode any P25 control channels at all. I've tried Motorola C4FM ones, Motorola CQPSK simulcast ones, and Harris C4FM. They all have really strong signals here, but none will decode. The screenshot below is from the PSR-800's "IF out" tuned to a Harris C4FM P25 control channel. It's really easy to adjust the "IF out" amplitude with the PSR-800, and I've tried all different levels with no luck.

Motorola 3600 control channels and EDACS 9600 will decode fine, though. If I click on the Scope tab at the bottom of the Receiver Discriminator screen, I do see the waveform, so I think I have the sound device selected right. I've tried changing the sample rate and sample size, and Polarity settings, but none allow any P25 decoding.

Most of my testing has been with only the checkbox for APCO P25 checked under Receiver Discriminator screen.

Any ideas?

 

[SCPD]

That's weird. Waveform looks good. You should see *something*.

The three sample rates 44100, 48000, and 96000 should work equally well. I recommend 16 bits for the sample size. Polarity doesn't matter for P25. It figures that out on its own.

If you can decode Motorola and EDACS - and the waveform isn't clipped - you should see a P25 site window. I can't think of a reason why this PC isn't working.

 

[johnoconnor98]

I'm new to Unitrunker and have a question. (I just bought a USB dongle and installed SDR# and Unitrunker last month)
I have an issue decoding P25 (I only have one P25 system in range, it's a Motorola system).
At first it decoded fine, then it just STOPPED, DOA.

By chance I was talking with one of the system techs and mentioned Unitrunker wasn't working on his system.
He got back to me and said his engineer had looked at it with his super-secret software and the site was not broadcasting the "SITE ID#". It was sending the SYSTEM ID but not the SITE ID. (this didn't seem to bother the user radios!?!)
He said they had "rebooted" the control channel, so I checked it and boom, Unitrunker was decoding the system again.

I notice with some Type II systems, I get a decode window that says "Site 0 Ad-Hoc" instead of a Site number.

So, my question is, should Unitrunker decode if the site is having issues? Like in Site-Trunking or not transmitting the entire system info?

 

[SCPD]

I think most folks would prefer the program bump along with something to display despite the lack of the site number. It is not normal for P25 systems to NOT announce their site # so this is unexpected behavior. I've seen this over the summer on one TxWARN site north of Houston.

Every trunking format is a bit different as you noted in your comparison to Motorola trunking.

As for the P25 site suffering partial amnesia ...

If the site was previously logged - I could find the site by matching the control channel frequency. That works for EDACS and Motorola (each for different reasons). However, on large wide-area networks - some control channel frequencies get re-used so this isn't a silver bullet solution.

If the site is a new discovery - things get messier still. I could use the site zero trick - except that (unlike Motorola and EDACS) - I think 000-000 is a valid site number. I'd have to use something numerically impossible like 256-000 as a placeholder site number until the site remembered itself.

 

[tbiggums]

I did finally get Unitrunker decoding P25 control channels on this machine. I'm not sure exactly what fixed it. I didn't change anything on the scanner or discriminator tap. I tried installing Unitrunker Retro, and it tried different sample rates and got it to decode a little bit. I do recall Retro showing it quickly switching back and forth between C4FM and CQPSK, for what that's worth...

Then going back to the current version, I tried starting and stopping decode frequently while changing sample rates and polarity settings, and finally got the site window to pop up. It's set to 44100 samples/sec and Auto polarity now.

 

[cg]

A friend of mine just ran into the exact problem with Unitrunker not seeing P25 systems and by luck figured it out. This was on systems that had previously worked with UT
He noticed that his sound card settings had changed from 48000 to 44100. This was not the settings in Unitrunker but the actual sound card settings in windows.
Changing back to 48000 let it work again.

chris

 

[SCPD]

Originally, Unitrunker only ran at 44100 sps since that was the only hi-fi sample rate commonly available back then. 48/96ksps were somewhat rate.

I don't know if this is related to Chris' comment but I have found that some audio device drivers will re-sample the audio if two or more programs access the same audio device.

If you are listening to music in WinAmp, for example, at 44100 and also trying to decode discriminator 48000 audio on the same audio device - the sound driver might pin the whole device at 44100 and re-sample the audio for Unitrunker decoding at 48000. Resampling always results in some distortion but the worst part is the additional latency.