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Unitrunker with 2 RTL dongles newbie

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#1
Hi All,

Just started playing with Unitrunker (latest version available)
I have 1 x RTL stick setup as a Signal receiver and another stick setup as a Voice receiver.

I've followed the instructions at RTL-SDR Tutorial: Following Trunked Radio with Unitrunker - rtl-sdr.com and I can get the Signal receiver to decode a strong local control channel with the health value mainly between 90 and 100 all the time.
The main window pops up automatically and shows me the system info that is being broadcast by the control channel, so this all looks like its working.

My problem is with the Voice receiver.
In the main window I see "calls" happening but I don't get any audio at all. I also see nothing on the Voice receivers scope and its status never changes from Parked.

Both sticks are calibrated so I already know their correction values which are setup correctly.
I've even swapped round my sticks so that the Signal one is now the Voice one and vice versa, but get the same problem.
Both sticks have been removed from Unitrunker and setup again from scratch several times.

Once thing I have noticed is that the "Frequency" column in the main window are all showing 0.0000.
I DO get data in the LCN, Target, T and Source columns.

The link above states that I need to click on an icon that looks like a calculator but I don't see that anywhere, so I guess that must have been based on an old version?

Both sticks work fine in other situations, FMP / DSD+, SDR Sharp etc.

I feel like I'm very close here but must be missing something.
The system I'm monitoring is at an airport. It is a quiet, small airport but I don't believe that there are no voice transmissions happening at all!

Can anyone help?
(I can provide some screenshots if it'll help?)

Thanks
enCrypt...
 

riccom

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#2
Check to see if the emphasis is on or not because sometimes the emphasis will a blackout boys channels from time to time of the day it happened on mine a few occasions best bet to do is see if that or maybe even move the antenna because sometimes the antenna will not receive in certain areas especially on a 700 or 800 MHz and system


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natedawg1604

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#3
What type of system are you trying to monitor? Unitrunker only decodes Audio for Analog protocols. If you wish to decode P-25 or other Digital protocols, the Unitrunker receiver must be piped to a third-party decoder such as DSD+, via a Virtual Audio Cable.
 

musicman476

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#4
Which system are you trying to monitor? UT can't decode P25 voice if that's what you're trying to do.
Edit: Looks like Natedawg beat me to it. :)
 

Dog

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#5
You need to enter all the channels manually. On the window that pops up click on the Home button "top left right below the strength meter. Then on the bottom click "Channels" Enter each one from the database. There isn't a "calculator" button anymore. (That I could find anyway.) I just went through this the other day. I thought I was going crazy. Once the voice receiver starts switching frequencies correctly then you can move on to if you need DSD+ or not.
 
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#6
Thanks for all the replies, I'll answer them in order...

@riccom, I struggled a bit to understand your post but I think you meant "de-emphasis". I've tried this on and off with no difference. The system I'm monitoring is in the 450Mhz range and I've tried the voice RTL stick on both rubber duck type antennas and a 2/70 antenna on top of my vehicle right outside the site!

@natedawg1604 and musicman476, It is an MPT1327 system (sorry I didn't mention that in my original post) which I'm pretty sure is just analog (is MPT1327 always analog?). I know about piping through digital audio to DSD+ with VirtualCable as I use that too. Also, I think even if it was digital comms I'd still see something on the voice receiver's scope, but I get nothing.

@Dog, you might be onto something there, but, I'm in the UK so the system will not be in the 'database'.
The signal receiver picks up that there are 3 channels but it doesn't populate the frequency into any of them.

What is confusing me is that when listening to the control channel on an analog scanner (which is how I found it, yes I'm sad and I now know what MPT1327 and MotoTRBO sound like by ear!) I don't hear any voice (or digital) channels around the same area.
I'm not sure if that is how these systems are normally setup, should I hear the voice channels near to the control channel on a normal radio?

Thanks
enCrypt
 
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#7
enCrypt - you'll need to find the voice channels. If a voice channel has a frequency of "0.000", the program won't bother trying to steer a voice following receiver to listen to the call.

Run a program like SDRConsole or SDR# to view the spectrum in the general area of the control channel. You'll need to do this while monitoring the Unitrunker site window for call activity. This will require a second SDR device.

As calls appear in the site window, the call should also appear as a new spike in the spectrum and waterfall. One you've confirmed the frequency for a particular channel number, update the channel (in the Calls tab or the Channels) frequency.

Repeat this process until all voice channels have been confirmed.
 
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#8
Thanks Unitrunker,

I had assumed that the frequencies used by the system would have automatically been gleaned from the control channel data, then fed to the voice receiver which would then follow them.
I hadn't realised that it was a manual process...

Does a "Call" in the site window always represent a voice call or can it be anything else?

And lastly, are MPT1327 systems always analog that you know of?

As stated it IS a very small system that I'm monitoring so it might just be that it it not being used much whenever I'm monitoring it!

Thanks all,

enCrypt
 

KD8DVR

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#10
Hmm...any system I've ever used, once the control channel is found, all the rest of the frequencies automatically populate, once the control channel directs traffic to one. On a p25 system, they all populate immediately.

AntiSquid Disclaimer: All posted content is personal opinion only and may not imply fact or accusation.
 
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#11
Thanks for your comment John KD8DVR

Yes that's exactly what I thought would happen too, it seems a bit strange having to put the other frequencies in manually to me, but maybe thats how MPT1327 systems work, not sure, never tried Unitrunker before...

I know there's not many or no MPT1327 systems in the States and there aren't many P25 systems in the UK apart from a couple of military bases, the last I heard...
 

natedawg1604

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#12
Hmm...any system I've ever used, once the control channel is found, all the rest of the frequencies automatically populate, once the control channel directs traffic to one. On a p25 system, they all populate immediately.

AntiSquid Disclaimer: All posted content is personal opinion only and may not imply fact or accusation.
Actually most trunked systems do not transmit system frequencies in the control channel; this would include LTR, EDACS, DMR and I believe Moto. Type II. I'm pretty sure MPT-1327 also doesn't include frequencies in the CC, it's a pretty ancient protocol.
 
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#14
Does a "Call" in the site window always represent a voice call or can it be anything else?
It can be voice or data. The data is low bit rate text, gps coordinates, or status like on-scen, package delivered, etc.


And lastly, are MPT1327 systems always analog that you know of?

The voice portion is always analog.
 
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#15
Thanks for the clarification Unitrunker, much appreciated.

Well, I guess I'll just keep monitoring to see what more I can find out about it.

Cheers all...
 
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#16
Well, for anyone else trying to find out more about any MPT1327 systems, I did as Unitrunker suggested and had one RTL stick monitoring the control channel watching when calls come in, and the second RTL stick running FMP (from DSD+)
When I saw a new peak on the spectrum display near to the control channel, I moved the cursor over it to find the frequency.
Then I knew what LCN corresponds to what frequency and entered that into the main Unitrunker window.
Once switching the second RTL stick back into Unitrunker Voice mode, it fired up on subsequent voice transmissions, so all is working ok.
There are 3 channels in this system, I've found 2 but the 3rd is eluding me at the moment! :)

Cheers all

enCrypt...
 
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