Can anyone offer assistance with getting Unitrunker to work with RTL-SDR?

[williaty]

I'm trying to get Unitrunker to scan the Ohio MARCS-IP system, which is Apco P25 Phase I. I have two RTL-SDR dongles and I'm trying to have Unitrunker run them directly. In SDR#, I found the control channel on one of the alternate frequencies and calibrated both dongles. The control channel is coming in about 10-12dB over the noise floor. I've been trying to follow the various instructions and tutorials for Unitrunker but all of them are either from before Unitrunker could control the RTL-SDR directly or from a few versions ago so none of the necessary settings are where the tutorials say they'll be. I'm pretty much hitting a brick wall trying to get Unitrunker going.

-I've installed and started Unitrunker
-I've clicked on the + to add a new Receiver
-In the dialog box that popped up, I selected RTL2832U
-In the Info tab of the Receiver configuration, I chose the RTL Device but I have no idea which of the two options correlates to which of the two physical dongles
-In the Info tab of the Receiver configuration, I set the correction to the same value I determined in SDR#. I'm assuming these are the same units so that -2 in SDR# is also -2 in UT. I've also tried both calibration values (-2 and 74) since I have no idea which dongle UT thinks is which.
-In the VCO tab of the Receiver configuration, I set the Role to signal.
-In the VCO tab of the Receiver configuration, I set the Park frequency to the frequency of the control channel.
-In the VCO tab of the Receiver configuration, I set the Mode to P25 since this is an Apco P25 system.
-In the VCO tab of the Receiver configuration under Listen, I de-selected everything except Apco P25.
-In the VCO tab of the Receiver configuration under Listen, I selected logging



With this setup, when I click Run/Start, I get static from the computer speaker but UT doesn't do anything. Where am I going wrong?

 

[mostar]

First things first, you need to determine which dongle is which...

Others may have figured out smarter ways,but here is what I do:

First, as you already did, find the correction value with SDR#. I have put a label on all of my dongles noting that value.

Now, in Unitrunker - just connect one dongle at a time.

So - plug in ONLY your dongle with the correction value of 74. Open Unitrunker, open the RTL Device drop-down and select the only device that shows up there. Enter the correction value of 74, put in your other info - lets assume this will be your signal device, so, the Control Channel freq, system type, etc.

Now, plug in the second dongle In the RTL Device drop-down, you should see the second device; select it, put the correction as '-2' (or whatever is appropriate), and continue to set this up as your voice receiver.

USB is funny...so, each time you reboot, or disconnect/reconnect the devices, you may need to repeat this process.

Again, others may offer a better way, but if not, this should get you pointed in the right direction.

 

[williaty]

OK, done. Sticks identified, receiver created with correction assigned to it, still getting static and nothing else.

 

[kb5udf]

Invalid Frequency

Check the frequency you are parked on, 744 or so, I believe is well outside
the 700mhz public safety band. You need to get on the frequency of an active control channel.
You should be able to obtain this by consulting the RR database.

Also, someone correct me if I'm wrong, but you should UNCHECK de-emphasis.

JB

 

[williaty]

Check the frequency you are parked on, 744 or so, I believe is well outside
the 700mhz public safety band.

Oh Christ on a crutch! You have no idea how long I've been struggling with this and it was just simple typo! This white-on-black interface is nearly impossible for me to read. Gives me a terrible headache to read the UT documentation pages because they're white-on-black as well.

So, UT is now spitting up all kinds of logging windows showing frequency assignments and whatnot.

Now, how do I go about getting the second dongle to follow what the control channel is issuing?

 

[williaty]

OK, after kb5udf caught the typo, I've made a little progress

-Unitrunker opened a logging window and started to show all kinds of information about what the system was doing
-I then clicked + to add a receiver again and configured it to use the 2nd dongle with the correct calibration.
-In the VCO tab under VCO, I set the Role to Voice
-In the VCO tab under Voice, I left the Audio Output alone
-In the VCO tab under Voice, I did not set the Digital Output because I don't have VAC and DSD+ setup yet
-In the VCO tab under Voice, I checked the Analog and P25 checkboxes

I then started the receiver. In the Info and VCO tabs, you can see it start to jump around frequencies to follow what the Control Channel is telling it to do. However, I'm getting no audio out of the speaker. I realize that UT can't provide demodulation of P25 Phase I, but I was expecting it to give me bursts of noise to tell me it was working like when I was testing the Control Channel receiver. Changing the analog output under VCO>Voice did not produce any noise

Is this expected behavior or do I still have something wrong?

 

[williaty]

OK, made some more progress but I've hit a problem I don't think is a matter of learning something. I've got all the software setup and Unitrunker is following the control channel, sending the other dongle to listen to the voice channels, and passing the result over VB-Cable to DSDPlus. The problem is I'm getting little to no decode out of DSDPlus. Mostly, it just fills the screen with error bars. Occasionally, I'll get a digital garble that you can tell is a voice but is messed up beyond all recognition. I've checked the CPU usage and it's running both cores to around 40% while it's working, so I don't think it's overloading the computer.

Is there any other options besides either weak receive giving insufficient signal to decode or the fact that this is a simulcast site producing too much multipath distortion to make this all work?

 

[mostar]

this may be helpful:

DSDTune - The RadioReference Wiki

 

[williaty]

Yep, I ran DSDTune and it suggested a bunch of filters that didn't help at all, sadly.

 

[SCPD]

Hi williaty;

Before pursuing voice following, work on your control channel decode rate.

You want that to be as close to 100% as possible. If the control channel isn't decoding well, DSD+ will likely have problems on the voice channel.

Play with the gain settings and antenna placement.

 

[williaty]

Where does it show me what the control channel decode rate is?

 

[SCPD]

You can see the numerical decode rate in the Signal section of the signal receiver's VCO tab.

http://www.unitrunker.com/r820t_signal.png

Look for the "Protocol" and "Health" fields.

 

[williaty]

OK, so I'm seeing Protocol set itself to APCO P25 and the health number is mostly in the 30s and 40s with occasional moments in the 60s. You're saying I need to get that Health number up to 100 in order to have a reasonable chance at doing the decoding?

 

[SCPD]

P25 sends out control channel messages at roughly 40 times a second.

If you miss one message, your decode rate is about 97%. The protocol sends duplicate messages so missing one is usually okay.

At decode rates much below 95%, your user experience will decline. You will

a) miss some calls
b) catch other calls already in progress
c) prematurely drop ongoing calls.

Run your favorite SDR program. Use the waterfall display to see what's in your RF environment. Move the antenna around and adjust the gain settings to maximize signal peaks, reduce the noise floor and suppress false images.

With your Realtek warmed up, zoom in on a known control channel to confirm that your correction PPM setting is accurate. Adjust as needed.

Using your 30 to 60% decode rate as an example, DSD+ won't be able to give you consistent audio when 40% or more of the bits can't be trusted. The voice channel has a lot of protection for bit errors but even that has limits.

 

[williaty]

Yeah, I plugged the dongle into an Arrow OSJ 144/450 that I have hanging from the ceiling and the Health numbers for the control channel now run 95-100 with the lowest I've seen being 87. Interestingly, looking at the spectrograph in SDR#, changing to that antenna doesn't improve the peak signal strength or reduce the noise floor, so I'm baffled as to why it's working better for following the control channel. I had initially disregarded that antenna because it's 50ohm, not 75ohm, and is tuned completely wrong. Somehow, it's better anyway.

I'm going over to Universal Radio tomorrow to see if they have a cheap antenna I can use to feed the 2nd dongle to track the voice channels. The problem is that their website doesn't list a MCX-to-anything adapter, so I suspect I won't be able to hook things right up. I ordered a MCX to F adapter off Amazon that they claim they'll deliver on the 4th (holiday and a Saturday and they still claim they'll deliver it?). I'll buy a F-to-N adapter at Universal tomorrow so I can use some LMR400 I got off a cell tower (which is N-terminated) to connect to whatever antenna I manage to rustle up tomorrow.

I'll report back once I've got an antenna situation sorted out. There's really nothing I can to until then.

 

[SCPD]

I had initially disregarded that antenna because it's 50ohm, not 75ohm, and is tuned completely wrong. Somehow, it's better anyway.

The impedance match is important for transmitting - not so much for receiving.

 

[slicerwizard]

The control channel is coming in about 10-12dB over the noise floor.

I doubt that'll be enough for DSD+.

Yeah, I plugged the dongle into an Arrow OSJ 144/450 that I have hanging from the ceiling and the Health numbers for the control channel now run 95-100 with the lowest I've seen being 87. Interestingly, looking at the spectrograph in SDR#, changing to that antenna doesn't improve the peak signal strength or reduce the noise floor, so I'm baffled as to why it's working better for following the control channel.

Perhaps it's not RXing any mulitpath signals.

If the signal is CQPSK, try -mp on the DSD+ command line.

 

[marksmith]

You can see the numerical decode rate in the Signal section of the signal receiver's VCO tab.

http://www.unitrunker.com/r820t_signal.png

Look for the "Protocol" and "Health" fields.

As long as you get the health into the 70's you should get some reliable decoding for just logging. Maybe not for voice though.

OK, so I'm seeing Protocol set itself to APCO P25 and the health number is mostly in the 30s and 40s with occasional moments in the 60s. You're saying I need to get that Health number up to 100 in order to have a reasonable chance at doing the decoding?

Mark
536/HP1e/HP2e/996P2/996XT/396XT/PSR800/PRO668/PRO652

 

[satboy8888]

When using two dongles, consider changing the serial number of one so they won't get mixed up when you reboot... The first one it sees will be one and the other a random name... It will work fine until you unplug or reboot the computer, then it'll be the lottery which is which after that. (Rebooting will play the lottery again, which may resolve it and may not). Check out the rtl_eeprom tool with the /s switch. As long as the numbers are different (1 vs 2), it'll always stay the same (signal vs voice).

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