Portable op25 Test rig for a P25 phase 2 system

[dimab]

I've been playing around with op25 software to decode and listen to a p25 phase 2 system in CT, specifically the CLMRN system. I've tried various setups, and it does a great job running on a raspberry pi 4. So for fun, I rigged this ugly duckling together and works just as expected. Still needs a lot of work. I even considered getting this to a smaller package and tucking into the console of my truck. My listening needs are minimal for the CLMRN system, so GPS or screen aren't needed.
Here is the break down -

• raspberry pi 4 (underneath the usb hub and rtl)
• op25 configured for 1 site
• 10,000mah battery
• JBL speaker
• RTL-SDR - nooelec v3
• USB hub - so I didn't have to have the RTL-SDR plugged directly into usb port and putting pressure on it
• some sort of 800mhz -ish antenna that came with the rtl

 

[dimab]

here is version 25. cleaned up

 

[markspoo]

Hi. Which pi app for the sdr are you using? Thanks in advance.

 

[dimab]

Hi. Which pi app for the sdr are you using? Thanks in advance.

op25

 

[markspoo]

Thank you.

 

[KN4EHX]

Wow, that looks wild. I get enough funny looks toting an APX with the large battery I can’t imagine whipping out that contraption while playing EMA. Certainly more economical than a $700 scanner. Check out SignalsEverywhere YouTube channel for a wealth of information on OP25.

 

[dimab]

Wow, that looks wild. I get enough funny looks toting an APX with the large battery I can’t imagine whipping out that contraption while playing EMA. Certainly more economical than a $700 scanner. Check out SignalsEverywhere YouTube channel for a wealth of information on OP25.

definitely NOT taking that out in public

 

[1979lee]

here is version 25. cleaned up

nice

 

[darkness975]

Certainly more economical than a $700 scanner.

I prefer the scanner.

But if all else fails I'm glad to hear there are other ways to listen to the system(s).

 

[KN4EHX]

I prefer the scanner.

But if all else fails I'm glad to hear there are other ways to listen to the system(s).

If anything it is an economical way for beginners to be able to listen to digital traffic. There is a very large learning curve to monitoring a digital or trunked system even with the $700 fancy pants scanner. Although everyone seems to be leaning towards encryption and that just takes the fun out of the sport of listening and learning. STEM needs a good boost and one of the ways to do that is innovation and interest. Kids will have a much more difficult time being able to use devices like this or digital trunking scanners without intimate knowledge of Linux or Microsoft depending on how much money they have to drop. My parents gave me a hand held CB when I was a kid, but my dad was a signal officer in the military and once every so often he would let me play with one of his radios and scan around to listen. Point being it was simple to turn a knob to find something happening, but now it isn’t so easy in many parts of the country. As for myself I can compliment my interest in radio as a child to my choice to go for a degree in science later in life.

For what it is worth I played radio nerd from my third story dorm room window. I was pretty surprised by how many people took interest in scanning through the bands. We literally chunked a wire out the window and worked the world - QRP of course - I didn’t want to radiate the neighbors.

To circle back to this topic, the cost is prohibitive for many people who might be getting into the hobby of listening. If anything this might be able to spark some interest and bring more people to the STEM community.

 

[riverradio68]

Like the JBL, how loud does that get?

 

[wgbecks]

I've been playing around with op25 software to decode and listen to a p25 phase 2 system in CT, specifically the CLMRN system. I've tried various setups, and it does a great job running on a raspberry pi 4. So for fun, I rigged this ugly duckling together and works just as expected. Still needs a lot of work. I even considered getting this to a smaller package and tucking into the console of my truck. My listening needs are minimal for the CLMRN system, so GPS or screen aren't needed.
Here is the break down -

• raspberry pi 4 (underneath the usb hub and rtl)
• op25 configured for 1 site
• 10,000mah battery
• JBL speaker
• RTL-SDR - nooelec v3
• USB hub - so I didn't have to have the RTL-SDR plugged directly into usb port and putting pressure on it
• some sort of 800mhz -ish antenna that came with the rtl

Have been running op25 Mobile for a few years now and it works pretty cool! I just wanted to jump in to comment that @boatbod added a feature to his Boatbod op25 fork a few years back that allows you to populate 0x0 as a NAC in the trunk.tsv file. This among other reasons does facilitate roaming about P25 SmartZone systems. Just program the CC's for the RFSS sites that you anticipate along your route of travel
and you're good to go.

Roaming with op25 is of course not as efficient as a well designed p25 radio in that the it has a five second control channel timeout before it will retune to the next frequency defined in the trunk.tsv control channel list. But still, it works quite well just the same.

 

[dimab]

Like the JBL, how loud does that get?

not sure how to quantify this - bu it's louder than I expected for such a small speaker, and sounds just fine while driving, or in the house

 

[dimab]

Have been running op25 Mobile for a few years now and it works pretty cool! I just wanted to jump in to comment that @boatbod added a feature to his Boatbod op25 fork a few years back that allows you to populate 0x0 as a NAC in the trunk.tsv file. This among other reasons does facilitate roaming about P25 SmartZone systems. Just program the CC's for the RFSS sites that you anticipate along your route of travel
and you're good to go.

Roaming with op25 is of course not as efficient as a well designed p25 radio in that the it has a five second control channel timeout before it will retune to the next frequency defined in the trunk.tsv control channel list. But still, it works quite well just the same.

interesting. looking at the web UI, I already see a bunch of adjacent sites listed, does that mean it's already picking up the neighbor sites?

 

[wgbecks]

interesting. looking at the web UI, I already see a bunch of adjacent sites listed, does that mean it's already picking up the neighbor sites?
View attachment 103495

No. This only shows that op25 is decoding the Adjacent Sites Status broadcast off of the current control channel.

When operating op25 in a "Mobile" configuration and you want to roam about within a SmartZone system, then you'll need to include the control channels and probably their alternates for each site (Tower) in your trunk.tsv file. Additionally, be aware that adjacent sites will have different NAC's. The work around is to set the NAC field in trunk.tsv to 0x0 whereby op25 will accept the first NAC received each time it acquires sync with a control channel.

Now, when driving out of the range from one site and into another, op25 will lose sync, will try to recover, but will eventually timeout and begin sequencing through the list of control channel frequencies until it reacquires sync with the system. While op25 was not actually written as a mobile receiving application, there will be a short interval once timeout occurs of no service but it's only a matter of seconds and depends on the number of control channels populated in the list that it has to test upon a timeout.