OP25 Single channel OP25 help

woobs420

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Hi first post here! Looking for some assistance getting a single channel non-trunking frequency to work. Our state police just went digital 460.3000 unknown NAC thus far. I have been trying to get this to work with OP25 on Ubuntu. I have thus far got OP25 boatbod installed. I am able to get it open and tuned to the frequency but don't hear anything. I see the instructions for setting it up for trunking with a control channel but here it's just a single channel. Does anyone have a link to general instructions for that or willing to help walk me through it? Or even any suggestions on a different program to listen with? My main PC is a hackintosh and also have an much older laptop with Ubuntu. sadly not much seems to be out there for mac though. I did also did some thread digging before posting but no luck. Thanks!
 

boatbod

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About the simplest command line for FDMA P25 Conventional would be:

./rx.py --args "rt" --gains "LNA:36" -f 460e3 -U 2> stderr.2
 

woobs420

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About the simplest command line for FDMA P25 Conventional would be:

./rx.py --args "rt" --gains "LNA:36" -f 460e3 -U 2> stderr.2
Thank you so much! I will give this a try after Ubuntu is done updating. Only thing is I have been typing "rtl" not "rt" Typo on you or me?
 

boatbod

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Should be rtl

./rx.py --args "rtl" --gains "LNA:36" -f 460e3 -U 2> stderr.2
Oops yes, thanks for correcting that.
As an aside, if the tuned frequency happens to be a trunked system, my version of op25 will automatically start tracking the trunking as soon as it sees the incoming TSBK messages.
 

woobs420

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Oops yes, thanks for correcting that.
As an aside, if the tuned frequency happens to be a trunked system, my version of op25 will automatically start tracking the trunking as soon as it sees the incoming TSBK messages.
It's just single channel best I can tell. This is North East Vermont aka middle of nowhere. I did re write the startup code a bit "./rx.py --args "rtl" --gains "LNA:36" -f 460.3e6 -U 2> stderr.2 -l http:0.0.0.0:8080" So I added the web interface and corrected the frequency. Seems to be working as in I can see the spectrum plot just waiting for traffic to see if it decodes. Could be mins or hours depending. With some help of other posts I did guess the NAC but honestly I have no idea how to set that up. Surprised I made it this far TBH.
 

woobs420

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Oops yes, thanks for correcting that.
As an aside, if the tuned frequency happens to be a trunked system, my version of op25 will automatically start tracking the trunking as soon as it sees the incoming TSBK messages.
Thanks it works! A question or two though if you don't mind. At first I got nothing even when there was signal I cranked the gain up to 49 and it started working but quite garbled also getting lots of PCM underrun errors. Maybe I went to far with the gain? Not much around for interference either. Waterfall looks dead adjacent for the most part. Are there any other gain controls? Looking at the waterfall it seems the might be some AGC going on as well.
 

dave3825

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What antenna are you using and the signal you see on the plot, is it dead on? Meaning your ppm is correct?

If your in the middle of nowhere, you may not need the nac if there are not other entities on the same freq being received.

General rule with gain, keep bumping it up until the signal reaches its highest point on the plot and the noise floor just starts to rise.
 

woobs420

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What antenna are you using and the signal you see on the plot, is it dead on? Meaning your ppm is correct?

If your in the middle of nowhere, you may not need the nac if there are not other entities on the same freq being received.

General rule with gain, keep bumping it up until the signal reaches its highest point on the plot and the noise floor just starts to rise.
Using a homebrew 1/4 wave 0dbi. I do have a higher gain Ed Fong one but the line runs to another part of the house for my GMRS repeater. Test with that when I can. The signal appears correct centerline is centered to the peak during a transmission. Also been using this SDR unit on other machines and the freq. always seemed correct. you are right about the NAC however I would like to know how to set it for a single channel anyways for future use. I have heard they might set up a repeater nearby with all State Police channels so I would need it there. I will try adjusting the gain although it's kinda hard as transmissions are very infrequent here sometimes nothing for hours but repeater ID's. Now if there was a way to adjust the gain while in operation that would be handy. I have been quitting op25 rewriting the start instructions and restarting. Kinda a pain. And my noise floor now is about -70.
 

dave3825

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Been a while since I messed with anything linux but I am going to get my Pi going real soon. I remember using gqrx to visually see the gains in real time so if you have that, tune to the freq and play with that. It should give you a better idea of the gain needed on OP25.

With little activity it does sound like a pain.
 

woobs420

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Been a while since I messed with anything linux but I am going to get my Pi going real soon. I remember using gqrx to visually see the gains in real time so if you have that, tune to the freq and play with that. It should give you a better idea of the gain needed on OP25.

With little activity it does sound like a pain.
I do have gqrx but not really sure how to compare as if I recall the gain is a slider type thing while here you set in during the start instructions. I will keep playing though not in any great hurry and taking my time to learn the lingo so to speak. Thanks for the advice!
 

dave3825

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do have gqrx but not really sure how to compare as if I recall the gain is a slider type thing while here you set in during the start instructions.

Op25 does require gain set up in command line but with gqrx, when you play with the slider, it displays the gain so if in that you see noise floor just start to rise around like 38, then 38 in op25 command line would be a good start.
 

woobs420

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Op25 does require gain set up in command line but with gqrx, when you play with the slider, it displays the gain so if in that you see noise floor just start to rise around like 38, then 38 in op25 command line would be a good start.
Just found that probably while you were typing. 42 seems in line with your suggestion. Now just a wait for traffic.
 
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