OP25 Playing with op25. Was really easy getting it working.

[LethalDosage]

It as really easy getting it working, listening to all talk groups. I could not find instructions for whitelisting, so I guessed and got it right.
I can't find any how-to docs. Do these exist?

I have some questions.
While running I see these lines:
At the top:
NAC 0x382 WACN 0xbee00 SYSID 0x389 856.212500/811.212500 tsbks 128785

In the middle:
voice freq 856.962500, active tgids [ 9608 ], last seen 0.3s, count 2914

On Maryland's FIRST system:
voice freq 774.268750, active tgids [ | 7314], last seen 0.4s, count 6
voice freq 773.018750, active tgids [ 7999| 8148], last seen 0.4s, count 4
voice freq 773.018750, active tgids [ 7999| ], last seen 0.8s, count 6

At the bottom:
Frequency 856.212500(10)
Or this:
Frequency 860.712500(10) Talkgroup ID 9606 15005

What are these?
811.212500 - from the top line
[ 7999| 8148] - from the middle. Why 2 talk group IDs? Sometimes, right, left or both, never 3 or more.
What is the (10) - from the bottom line. This number changes.
15005 - from the bottom line. This number changes. Handset number?

My frequency range is about 854.562500 to 860.712500, so I need 2 radios, maybe 3. How can I tell?

SDRtrunk allowed me to set the bandwidth to about 2.8Mh, is this a good idea? If so, how with op25?

With 1 radio I still hear the talk groups that are out of range of the control freq, is the radio changed to get only the talk group and then switches back to the control when done? It seems to not work like this because I see updated talk group info while I am listening to a talk group that is at the extreme end of my range (860.712500). I only have 1 control freq. defined, and it is 856.212500.

If I define 2 or more control frequencies, will op25 decode them at the same time, or switch, or what?

I really hope to stream to broadcastify. Is there a how-to for this?

I really hope to have 2 or more streams from 2 or more talk groups, can this be done?

I see "--sample-rate". How do I know what sample rate is best for the system I am listening to? I want CD quality! 44,100, 16 bit stereo!
op25.sh has "-S 960000". I have no idea how that equates to anything! Beyond CD quality!!??

Is there a doc that describes the options in more detail than "./rx.py -h"?

I know this is a lot of questions, feel free to send me to a web page with info. I can read it, if I can find it!

I don't think I have a use for ./multi_rx.py, but I would like to read about it. Any docs? "--help" shows 4 options and 1 of them is "--help"!

Thanks,
Guy

 

[maus92]

Yup, a lot of questions. Screen shots are helpful.

OP25 only needs one SDR to cover systems as it dynamically retunes the SDR off the control channel to a voice (traffic) channel. It uses data in the traffic channel to maintain connectivity when voice is being decoded.

 

[LethalDosage]

Yup, a lot of questions. Screen shots are helpful.

OP25 only needs one SDR to cover systems as it dynamically retunes the SDR off the control channel to a voice (traffic) channel. It uses data in the traffic channel to maintain connectivity when voice is being decoded.

Screenshots - yes, should have done that. But with the text I could easily change the color of the bits I was asking about.

Ok, cool, so the traffic channel also gets the control info? Makes sense, then the police radios only need 1 receiver. If I only listen to 1 talk group at a time, then 1 radio can do it. So far I only know how to listen to 1 talk group at a time!

Thanks for the quick response!

What about my other 99 questions?

 

[boatbod]

It as really easy getting it working, listening to all talk groups. I could not find instructions for whitelisting, so I guessed and got it right.
I can't find any how-to docs. Do these exist?

There's no PDF manual or anything like that, but there are some READMEs and examples included in the distro. It's a weak area however.

I have some questions.
While running I see these lines:
At the top:
NAC 0x382 WACN 0xbee00 SYSID 0x389 856.212500/811.212500 tsbks 128785

856.2125 is the output frequency (RFSS to subscriber)
811.2125 is the input frequency (subscriber to RFSS)

In the middle:
voice freq 856.962500, active tgids [ 9608 ], last seen 0.3s, count 2914

On Maryland's FIRST system:
voice freq 774.268750, active tgids [ | 7314], last seen 0.4s, count 6
voice freq 773.018750, active tgids [ 7999| 8148], last seen 0.4s, count 4
voice freq 773.018750, active tgids [ 7999| ], last seen 0.8s, count 6

These show each of the voice channels assigned to the RFSS as well as any currently active tgids. A single voice frequency can have none, one or two voice calls active at a time, depending on mode of operation. The 'last seen' timer is the number of seconds since this voice frequency was last active and the counter is how many times it has been used since op25 started.

At the bottom:
Frequency 856.212500(10)
Or this:
Frequency 860.712500(10) Talkgroup ID 9606 15005

This is the currently tuned frequency and (if a call is active) the current talkgroup, tgid and slot id.

My frequency range is about 854.562500 to 860.712500, so I need 2 radios, maybe 3. How can I tell?

SDRtrunk allowed me to set the bandwidth to about 2.8Mh, is this a good idea? If so, how with op25?

These days I usually recommend to set an RTL sample rate to "-S 1000000" as it works well on most any computer regardless of how good the cpu is. There's really not much call to go higher (due to the way op25 works) unless you are running multi_rx.py and wanting to receive multiple simultaneous channels with shared sdr hardware.

With 1 radio I still hear the talk groups that are out of range of the control freq, is the radio changed to get only the talk group and then switches back to the control when done? It seems to not work like this because I see updated talk group info while I am listening to a talk group that is at the extreme end of my range (860.712500). I only have 1 control freq. defined, and it is 856.212500.

op25 will retune the rtl dongle as needed to reach any frequency. There is a small time penalty for this, but retuning generally completed in 700msec or under, so practically the benefits outweigh the cost.

If I define 2 or more control frequencies, will op25 decode them at the same time, or switch, or what?

This is a tricky area to explain. If you list more than one control channel in a comma-separated list for a single P25 system, op25 will start with the first freq in the list and look for a control channel. If found, it will stay there until the signal goes away. If not found (consecutive timeouts) op25 tuns the next control chan freq and so on, and keeps cycling around the list looking until it finds something.

In rx.py if you define multiple P25 systems (on separate lines of trunk.tsv) op25 will look for activity on the first system and if there is none it will retune to the second system and look there, basically switching between the two systems when they are idle. IMO it's a horrible idea (legacy behavior, like a classic scanner) which is hard to listen to because you can't predict when it will switch over. My version of multi_rx.py does away with this and allows you to simultaneously monitor multiple TGIDs and even separate P25 systems by sharing and/or running multiple sdr dongles in parallel. There is no hard limit to the number of simultaneous channels other than having sufficient sdr resource and cpu abilities. For example a RPi3b can just run one channel whereas an Intel i5 system can run 3+ channels.

I really hope to stream to broadcastify. Is there a how-to for this?

Check the "README-rpi3-liquidsoap" in the top level op25 directory. An example script (op25.liq) is included.

I really hope to have 2 or more streams from 2 or more talk groups, can this be done?

Certainly. See my comments on multi_rx.py and also the example .json files for ideas how to set it up. If you get stuck just PM me.

I see "--sample-rate". How do I know what sample rate is best for the system I am listening to? I want CD quality! 44,100, 16 bit stereo!
op25.sh has "-S 960000". I have no idea how that equates to anything! Beyond CD quality!!??

LOL
PCM rate is fixed at 8000Hz 16bit LE. Sound quality depends a lot on the settings used by the RFSS that you are listening to, as well as your receive signal strength. If rx strength is too low, you'll get increasing bit errors and dropouts on the audio. The forward error correction (FEC) can only correct a finite number of errors before it craps out. If the audio level is low, you can either boost it linearly using the -x parameter, or use liquidsoap to do DSP compression/leveling.

(SDR sample rate - which is something unrelated to audio sample rate - can be happily set to "-S 960000" or "-S 1000000" as discussed above)

Is there a doc that describes the options in more detail than "./rx.py -h"?

Various READMEs and example files exist in the distro. Sorry, it's weak but I spend too much time on the code and not enough on the documentation.

I know this is a lot of questions, feel free to send me to a web page with info. I can read it, if I can find it!

I don't think I have a use for ./multi_rx.py, but I would like to read about it. Any docs? "--help" shows 4 options and 1 of them is "--help"!

Thanks,
Guy

 

[LethalDosage]

Ok, good info. I this should keep me busy for awhile.
Thanks!