OP25 Building the thinest client to run a mobile Smartnet radio

[maus92]

I'm currently running Buster on a Pi 4 decoding a busy Smartnet system. Unfortunately, its CPU is about maxed out all the time according to htop. I'm not sure if the device is thermally throttled (although it's mounted in an active heatsink case,) or the processing of an mostly analog simulcast system is just too much work for the hardware (a similar setup runs much better on an old NUC.) The audio is several seconds behind a hardware radio sitting next to it, which is to be expected. The interesting thing is that digital tgs are more reliably reproduced than the analog tgs. In other words, many analog transmissions are simply missed. Anyway, I want to cut down on running processes as much as possible. I'm probably going to reflash the OS - but what OS to use?

 

[wgbecks]

I would advise against trying to operate a Mobile SmartNet implementation of op25 whereby the system has analog talkgroups of interest. The reason being is the lack of a true noise operated squelch function being available in GNU Radio, the base of op25.

You'll find that you can tweak squelch levels to provide satisfactory performance in comparison to the digital talkgroups while operating at a fixed location where signal levels are fairly constant. However, all bets are off when attempting to operate mobile using this software platform.

With regard to CPU loading, you should be using two SDR's one for the control channel and once for the voice channel receiver using a minimal sampling rate for each SDR as a means to reduce loading on hardware and OS resources.

For mobile applications where SmartNet is concerned, you'd be better off with a scanner designed for this type of trunk system or perhaps a surplus commercial grade radio setup for passive monitoring.

Bill

 

[maus92]

I would advise against trying to operate a Mobile SmartNet implementation of op25 whereby the system has analog talkgroups of interest. The reason being is the lack of a true noise operated squelch function being available in GNU Radio, the base of op25.

You'll find that you can tweak squelch levels to provide satisfactory performance in comparison to the digital talkgroups while operating at a fixed location where signal levels are fairly constant. However, all bets are off when attempting to operate mobile using this software platform.

With regard to CPU loading, you should be using two SDR's one for the control channel and once for the voice channel receiver using a minimal sampling rate for each SDR as a means to reduce loading on hardware and OS resources.

For mobile applications where SmartNet is concerned, you'd be better off with a scanner designed for this type of trunk system or perhaps a surplus commercial grade radio setup for passive monitoring.

Bill

Rats. How minimal on the sample rates? I think I'm set at 1M. I am currently running my old GRE PSR800 on the system, but I find it marginal / unsat in many areas - my county has a 10 site SmartZone system that pumps out a lot of power, too much sometimes for the scanner to handle even when attenuated or using a crap antenna. I do own a nice XTS5000, but unfortunately I don't have the software to program it, and the moto shop is only interested in programming it if the county will assign it an RID (which understandably they don't want to do, lol.)

 

[wgbecks]

The 1M sample rate is about optimum but some may argue you can go a lot lower. I only mentioned sample rate because many times I've seen RTL SDR's maxed out at 2.56M that does directly impact CPU loading.

Sorry to quash the idea of using op25 SmartNet in a mobile application but you'll never strike a happy medium in trying to optimize the squelch for the analog receiver function so long as GNU Radio doesn't include a true noise type squelch. In fact, AFAIK there is no other SDR application that works any better in this regard.

Your XTS5000 would have to have the correct flash features before it could be pressed into a passive scanner and all of the implications that brings with it if not done correctly. I can't advise if any of the newer scanners are any better on decoding SmartNet systems that employ simulcast, probably not with the emphasis on P25 with so few SmartNet systems left on the air.

Good luck!

 

[cg]

My experience with a Simulcast Smartnet system and the BCD996XT & P2 was that it worked fine. The P25 P1 replacement system worked fine as well. It went downhill with the Phase 2 implementation though.
You might be able to run Trunk88 using a SDR on a decent ThinClient but it needs Windows. Unitrunker is another software solution but again, Windows.

chris

 

[maus92]

The XTS has the features to run on the system, I just don't have the software or expertise to set it up properly. I used to own a 436 and a SDS100. The 436 was poor on this system, while the SDS100 that replaced it was a little better particularly with the digital side. The analog was still not so good. Surprisingly, the 536 does pretty good IF I use a remote antenna stuck to a window or a repurposed SDR kit antenna - back of the set antenna perform poorly. I actually tested UT2 today in the Tesla with a BT remote speaker and a Dell 2 in 1 - it worked fairly well for the short time I used it, but it was awkward. In about two years, the county will be using its new P25P2 system and my G5 should work fine if it wasn't crippled by the 300mw audio power output (ok for indoors / quiet places, but not noisy vehicles) and obsolete BT hardware. The GRE is surprisingly loud.