OP25 OP25 No Audio output.

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VA4JOE

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Ok, so had to change trunk.tsv again, now getting tsbks' again and proper frequencies listed. Still not getting any audio though.
 

boatbod

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Ok, so had to change trunk.tsv again, now getting tsbks' again and proper frequencies listed. Still not getting any audio though.
I'll need "-v 11" detailed logs and screen shots of the plots when tuned to voice channel as requested in my previous post please.
 

VA4JOE

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My op25 seems to work best with this command so far:
./rx.py --args 'rtl' -N 'LNA:47' -S 1000000 -f 770.19375e6 -o 25000 -D fsk4 -q 0 -T trunk.tsv -U -V -v 10 -X 2> stderr-stream0.2
...gets it closest to the frequency...but no audio...I took out the -2 because I think it is phase 1...doesn't do audio either way...
 

VA4JOE

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Will try to get those plots to you...the top line is stable for a while then drops out...still trying to get the best -q value...

Going to friends to watch some CFL football...maybe try again tomorrow...
 
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boatbod

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My op25 seems to work best with this command so far:

...gets it closest to the frequency...but no audio...I took out the -2 because I think it is phase 1...doesn't do audio either way...
I really must retire that "-2" option and make it simply default to on. There is no benefit in not including it...
How old is your dongle? Most of the current generation don't need an offset (-o 25000) to avoid the dc spike because they don't have one to start with. Either way, I doubt that's significant because it doesn't seem to affect your ability to receive the control channel.
 

wgbecks

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Joeseph,

The receive timeouts that you're experiencing may be due to radio frequency interference that could be coming from nearby
electronic devices or perhaps from a 700 MHz LTE site. To make any such determination, we'll need spectrum (FFT) plots made
with the SDR tuned to specific frequencies.

From the logfile you emailed to me, I was able to extract the frequencies of the primary and alternate control channels in addition
to four others that consistently fail to decode whenever voice traffic is assigned to them.

Primary Control Channel: 770.20625
Secondary Control Channels: 770.70625 and 770.95625
Voice Trunk Channels: 771.20625, 771.45625, 771.70625, and 771.95625

I would like you to shutdown op25 then using GQRX, tune in the last know active control channel of 770.20625 and carefully
apply frequency (PPM) corrections as necessary to center the spectrum on the red vertical centerline. It should resemble the
example shown below. It is important for this operation to set the Frequency zoom to a value for your SDR and sample rate
that produces a similar spectral display as the example.

With GQRX now setup, tune in each of the Voice Trunk Channels as listed above, one at a time, and make screen captures of the
FFT display, then post those to the forum that we can try to determine if there is any radio interference or other reason for a
high noise floor that may be impacting decodes.


GQRX.png
 

VA4JOE

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VF3-Manitoba-gqrxFFT.pngVF1-Manitoba-gqrxFFT.pngVF1-Manitoba-gqrxFFT.pngVF1-Manitoba-gqrxFFT.pngVF1-Manitoba-gqrxFFT.pngVF2-Manitoba-gqrxFFT.pngVF3-Manitoba-gqrxFFT.pngVF4-Manitoba-gqrxFFT.pngVF4-Manitoba-gqrxREC.pngVF3-Manitoba-gqrxREC.pngVF2-Manitoba-gqrx.pngVF1-Manitoba-gqrx.pngCC1-Manitoba-gqrx.png

I'm sorry if I posted multiples. There should be one Control Channel and two voice channels pics for each voice frequency, one with receiver image and one with FFT image. I'm feeling under the weather today, sorry.
 

wgbecks

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When your well enough, I am interested in GQRX capturs while tuned one at a time
to the following "Voice Trunk" channels; 771.20625, 771.45625, 771.70625, and 771.95625.
 

VA4JOE

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When your well enough, I am interested in GQRX capturs while tuned one at a time
to the following "Voice Trunk" channels; 771.20625, 771.45625, 771.70625, and 771.95625.
I think all those frequencies are off to the side a little bit from these numbers on my dongle. At least that is what I believe. They are already captured on the previous post. Could the Control Channel be a wild goose chase?
 
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lwvmobile

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Just from looking at your screenshots of GQRX, I would wager your PPM is off significantly, and perhaps OP25 can't find the proper error on it with such a wide difference. If I may demonstrate. What you want to do is put the frequency for the control channel (or a voice channel) in as the tuned frequency in GQRX (don't adjust the frequency to match the actual RF signal). For example. Here I am tuned to 851.375Mhz which is the frequency I want, but the PPM is set incorrectly (intentionally so for demonstration). If you click on the input control tab and manually adjust the Freq. correction arrows up and down, the signal in the waterfall will begin to shift closer or further away from the target signal.

Screenshot from 2023-07-30 00-29-00.png

What you want to do is find the ppm value where your red line is dead center (or as close as it gets to that RF signal.

For example, if I were using your commands, and you were currently using



Screenshot from 2023-07-30 00-29-19.png

When you ascertain this PPM value, this will be the -q value you wish to use when calling rx.py.

./rx.py --args 'rtl' -N 'LNA:47' -S 1000000 -f 770.19375e6 -o 25000 -D fsk4 -q 0 -T trunk.tsv -U -V -v 10 -X 2> stderr-stream0.2

I would change the underlined portion from -q 0 to the value that you found for the correct PPM error, in my case, that would be -q -3

In your case, judging by how far those frequency values are off, I would guess the ppm error could be much higher (or much lower) such as 48-52 or negative 48-52. I do have one dongle whose PPM error is off that much, but its consistently off by that much, so just knowing that value, I can still use it well enough.
 

boatbod

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PPM values more that +/-0-3 are usually indicative of a non temperature compensated dongle. They can be made to work with op25 quite successfully, but you have to get them warm (i.e. use them for a while) before you figure out the ppm correction.

Can the op please identify the brand and model of RTL device in use please.
 

VA4JOE

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PPM values more that +/-0-3 are usually indicative of a non temperature compensated dongle. They can be made to work with op25 quite successfully, but you have to get them warm (i.e. use them for a while) before you figure out the ppm correction.

Can the op please identify the brand and model of RTL device in use please.
It's blue in color, bought by me a few weeks ago from china. It says "NEW GEN. RTL2832" and under that "R828D & SDR". It has a small 800mhz antenna with it. The connector for the antenna is tiny and plugs(not screws) into the dongle. The "lsusb" shows "Bus 002 Device 002: ID 0bda:2838 Realtek Semiconductor Corp. RTL2838 DVB-T"
RTL-SDR.JPG
 

VA4JOE

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What if the control frequency is dead on but the voice frequencies need +16 correction?
 

lwvmobile

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./rx.py --args 'rtl' -N 'LNA:47' -S 1000000 -f 770.19375e6 -o 25000 -D fsk4 -q 0 -T trunk.tsv -U -V -v 10 -X 2> stderr-stream0.2

07/26/23 12:06:59.250690 [0] tsbk(0x3a) rfss_sts_bcst: syid: 9ee rfid: 1 stid: 88 ch1: 1520(770.206250)
07/26/23 12:06:59.251048 [0] tsbk(0x3b) net_sts_bcst: wacn: bee00 syid: 9ee ch1: 1520(770.206250)

Are you still starting up with this frequency loaded? The command you are using has frequency 770.19375 but the RFSS indicates it should be 770.20625
 

VA4JOE

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Ok So now I changed the CC to 770.20540 and the "q 16" and I am getting some garbled voice with some encrypted voice as well. Changed CC to 770.20625 and get same garbled voice with some encrypted.
 

lwvmobile

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Probably isn't catching the HDU or MAC_PTT to get the initial encryption identifiers, and only silences when it gets a completed LDU2 or ESS from the superframe. That'd be my guess. PPM could still be a partial problem if it doesn't land dead center, it may take a brief split second to adjust properly and demodulate good dibits.
 

boatbod

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Probably isn't catching the HDU or MAC_PTT to get the initial encryption identifiers, and only silences when it gets a completed LDU2 or ESS from the superframe. That'd be my guess. PPM could still be a partial problem if it doesn't land dead center, it may take a brief split second to adjust properly and demodulate good dibits.
Retune time is approx 750-800msec so it's not unusual to miss the HDU. Limitation of the current op25 demodulator unfortunately.
 
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