OP25 - Is an original Pi3 good enough?

[W2SJW]

Guys,

I have an original Pi 3B here at the house that I wanted to press into service to play around with on OP25. I live less than 5 miles from one of the biggest TX sites here in North Jersey for our statewide 700MHz interop system.

This picture seems to show that I've got the thing set up correctly, but when I put a set of headphones on the device, the audio is only giving me 'burps & blurbs' of words. If the fact that I only have it on a 2A power supply a possible issue? Is the Pi 3B not powerful enough? I followed the 'OP25 For Dummies' blog to set my unit up, and it seems to have went as good as John said it should have (I did get CMAKE warnings during that stage of the compile, and I get warnings that the PLL on my RTL-SDR v3 isn't locked.

Any other great locations for follow-up info so I can read up more on how to make this work better?

 

[a417]

Yes. How long was that instance running that you took the screenshot of? 1300 tsbks is not a lot...is it constantly incrementing? And you're VNC'ing to that Raspi?

 

[lwvmobile]

Try running the command: htop in another console window while OP25 is running and see how much CPU its using. If its constantly pegged out at full usage, or somewhere in the middle? If its constantly pegged out, it could be that the CPU isn't keeping up. I've used 2 SDR dongles on a Pi 3b+ before myself no issues with power, but that was also a 3A Motorola Turbo charger, so I honestly don't know how much power it was pulling total.

 

[schlever]

You may be slightly off-tune. Have a look at the scatter plot and ensure your getting 4 tight circles on those control frequencies. If not, your PPM on the dongle may be slightly off and you have to adjust that using the f command in your initialization string. If that looks good have your tried listening on the HDMI audio channel. I had a heck of a time with the audio out jack on mine and switched to the HDMI for audio.

I follow a Phase 2 system here on a 3B+ with no issues on a 2 amp power supply.

 

[W2SJW]

I was VNC into the Pi. It was up for maybe 5 minutes at that point. I will start it up right now & let it go for about 30 minutes. I will check the CPU usage as well. The RTL-SDR v3 units are always -2 when warmed-up, as that was what these sticks always needed when running UT on my PC.

 

[W2SJW]

OK, the tsbks are incrementing (quite briskly). this is what the unit is reporting for resource usage. I have nothing I can use to try and extract the audio out via HDMI right now, though.

 

[W2SJW]

Also, nice tight circles on the constellation plot view:

 

[boatbod]

Some questions/suggestions:-

i. Minimize the SDR sample size to 1000000 or less. This lowers the load on the cpu caused by data transfer and IQ filter processing.
ii. Experiment with "-O default" vs "-O pulse" to see if one or other works better with less stutter.
iii. Make sure you are using a 4-pole headphone jack. It's a known thing that using a regular 3-pole stereo jack can cause issues on a RPi
iv. Once the tuning is correct turn off all the plots. They consume too much cpu on the RPi3 and cause stuttering/underruns.

 

[a417]

audio over VNC stutters and lags as well, so you could be experiencing an audio issue after OP25.

 

[lwvmobile]

You might try connecting to the audio stream remotely instead of doing it through UDP, I'm just going to paste a couple links with small snippets.

op25/op25/gr-op25_repeater/apps/README at master · boatbod/op25

Fork of osmocom OP25 by boatbod. Contribute to boatbod/op25 development by creating an account on GitHub.

github.com

REMOTE TERMINAL
===============
Adding (for example) "-l 56111" to the rx.py command starts rx.py but does
not attach a curses terminal.  Instead the program runs as normal in the
foreground (hit CTRL-C to end rx.py as desired).  To connect to a running
instance of rx.py, (in this example)
    ./terminal.py 127.0.0.1 56111
NOTE: rx.py and terminal.py need not run on the same machine.  The machine
where terminal.py is running need not have an SDR device directly attached;
but GNU Radio (and OP25) must be available.

WARNING: there is no security or encryption on the UDP port.

EXTERNAL UDP AUDIO SERVER
=========================
Starting rx.py with the "-w -W host" options directs udp audio data to
be sent over the network to the specified remote host.  It can then be
received and played back with either of the following methods:
1. Execute ./audio.sh on a remote machine equipped with python2.7,
   libasound.so.2 and the sockaudio.py file.
-or-
2. Execute the command:
   nc -kluvw 1 127.0.0.1 23456 | aplay -c1 -f S16_LE -r 8000
-or-
3. Execute the command:
   vlc.exe --clock-jitter=500 --network-caching=0 --demux=rawaud --rawaud-channels 1 --rawaud-samplerate 8000 udp://@:23456

NOTE: audio underruns are to be expected when using nc | aplay as the
pcm stream is interrupted every time a radio transmission ends.  The
sockaudio player is designed to handle this more gracefully, and generally
only underruns due to high cpu utilization or reception/decoding errors.

Also, check this prior forum post about a similar thing.

OP25 - OP25 Remote Terminal

I managed to set up OP25 running on a spare PC and use -w -W 192.168.0.X1 -l 56111 arguments to allow me to get the audio and make the remote terminal available to another local PC. I can access the terminal using ./terminal.py 192.168.0.X2 56111, but after about 10 minutes the ./terminal.py...

forums.radioreference.com

 

[W4KRR]

If I want to set up OP25 on a Raspberry Pi 4, can I get sufficient audio from the jack on the Pi, using a speaker or headphones? Will there be a noticeable performance difference between a 4gb and an 8gb RAM model?

 

[a417]

If I want to set up OP25 on a Raspberry Pi 4, can I get sufficient audio from the jack on the Pi, using a speaker or headphones? Will there be a noticeable performance difference between a 4gb and an 8gb RAM model?

RAM difference if you're just running OP25? None. I am running it on a Raspi 2B with 1gig and it just works.

 

[lwvmobile]

You might try connecting to the audio stream remotely instead of doing it through UDP, I'm just going to paste a couple links with small snippets.

Correction: You might try connecting to the audio stream remotely instead of doing it through UDP VNC/RDP.

 

[lwvmobile]

RAM difference if you're just running OP25?

I wonder how many Chromium tabs one would have to open to use the full 8GB on a RPi 4. It takes me opening up a VM or a game to get close to that on my workstation PC. I think I had to open 4 VMs to push up towards the 16GB I have.

 

[W4KRR]

I wonder how many Chromium tabs one would have to open to use the full 8GB on a RPi 4. It takes me opening up a VM or a game to get close to that on my workstation PC. I think I had to open 4 VMs to push up towards the 16GB I have.

So, 8GB of RAM for OP25 is overkill, I gather?
What about audio? Will it drive a speaker plugged into the audio jack?

 

[lwvmobile]

So, 8GB of RAM for OP25 is overkill, I gather?
What about audio? Will it drive a speaker plugged into the audio jack?

Yeah, I'd definitely say the 8GB model is most likely extremely overkill. As far as will it driver a speaker plugged into the audio jack, I couldn't tell you. I don't recall hearing of any issues with the audio/composite jack, but I honestly have never used it on my 3b+ either. I don't own a 4, but I have been trying to talk myself into Raspberry Pi 400 lately, but I don't know what I would honestly do with it other than pretend its a Commodore 64 or something.

 

[a417]

It will drive an amplified speaker just fine.

As for the 400, first thing I thought of was "hey, it's a white Timex Sinclair 1000!"

 

[W2SJW]

Some questions/suggestions:-

i. Minimize the SDR sample size to 1000000 or less. This lowers the load on the cpu caused by data transfer and IQ filter processing.
ii. Experiment with "-O default" vs "-O pulse" to see if one or other works better with less stutter.
iii. Make sure you are using a 4-pole headphone jack. It's a known thing that using a regular 3-pole stereo jack can cause issues on a RPi
iv. Once the tuning is correct turn off all the plots. They consume too much cpu on the RPi3 and cause stuttering/underruns.

These 3 things did the trick! I've got a pair of 4-contact earbuds that came with a previous Samsung phone that I was able to test with. Lowering the sample size from the John's 2500000 to 100000 made the most improvement (he's showing in his guide that he has it running on Ububntu, probably on a laptop, so that might mean he's got more horsepower to throw around).

This is what I'm running as my execute string right now:

./rx.py --args 'rtl' -N 'LNA:47' -S 1000000 -x 2 -f 773.83125e6 -o 17e3 -q -2 -T trunk.tsv -V -2 -U 2> stderr-stream0.2

Now if I can figure out how to properly set up Liquidsoap & icecast2...

 

[boatbod]

So, 8GB of RAM for OP25 is overkill, I gather?
What about audio? Will it drive a speaker plugged into the audio jack?

op25 doesn't need 8GB, nor will the regular 32bit Raspbian OS image be able to utilize 8GB. If you plan on using that Pi4 for something else as well as op25 I'd recommend you install the 64bit Raspbian Beta. All my Pi4s are running 64bit and op25 builds/runs quite happily.

 

[W4KRR]

op25 doesn't need 8GB, nor will the regular 32bit Raspbian OS image be able to utilize 8GB. If you plan on using that Pi4 for something else as well as op25 I'd recommend you install the 64bit Raspbian Beta. All my Pi4s are running 64bit and op25 builds/runs quite happily.

Thanks! I actually ended up ordering the Pi 400, which the Pi 4 is built into a keyboard (4GB RAM). I hope that doesn't present any problems for OP25, especially after I found out it doesn't have an audio jack! However I have a 7 inch HDMI display that has built in speakers, hopefully I can utilize those.