SDR# and DSD+ Not Decoding MotoTrbo

[rkillins]

Im am trying to decode Motortrbo audio from a local Mototrbo frequency 172.9500 using SDR# and DSD# software. Also installed is VB-Cable v.4.3
My antenna is connected to my computer (Win 8.1) with an RTL-SDR(USB) dongle.

In SDR#, the source is set to RTL-SDR(USB). Radio NFM, Bandwidth 10, no squelch. SDR# is tuned to 172.9500
Audio ...
Samplerate 48000 sample/sec.
Input: [MME] Microsoft Soun (the option to select is disabled, I can't seem to be able to change this);
Output: [MME] CABLE Input (VB-Audio Virtual Cable)

I have this frequency tuned into my scanner as well, so I know when a signal is being broadcast. WIth SDR# engaged, I can see the spike on the scope when a transmission is broadcast. I assume SDR# is getting the signal.

When I start DSDPlus.exe, the status window displays:
audio input device #1 = 'CABLE Output (VB-Audio Virtual '

audio output device #1 = 'Speakers (Realtek High Definiti'
audio output device #2 = 'CABLE Input (VB-Audio Virtual C'

audio input device #1 (CABLE Output (VB-Audio Virtual ) initialised
audio output device #1 (Speakers (Realtek High Definiti) initialised

I am not able to hear any decoded audio? DSD+ does not reflect any event log activity on the scope. Does my setup look correct? Has anyone any suggestions on why this may not be working?

 

[mrlindstrom]

Any reason you’re not just using DSDPlus to tune the frequencies? My video is a little old now but most of the info should still be good:

Edit: just realized I used sdr# myself in this vid... however DSDPlus can control the rtl device and you might try that route to remove virtual audio cable from the equation.

Some of my other p25 videos go that route.

 

[Ubbe]

Everything looks ok except bandwidth. It is not 10, it should be 12500.

/Ubbe

 

[slicerwizard]

Everything looks ok except bandwidth. It is not 10, it should be 12500.

Why? DMR signals are what, less than 8 kHz wide?

For the OP: I see no mention of PPM correction. And you really should be posting a screen shot or two.

 

[Ubbe]

Bandwidth are stated in Hertz and 10Hz are not enough, it has to be 12.5Khz.

The usual stuff in the cogwheel settings needs of course to be correct as well but shouldn't make the decoding go deaf if you can see the signal on the spectrum display and you are pinned to it.

/Ubbe

 

[cg]

Bandwidth settings for the Motorola Con+ systems I monitor all are very happy using 7.6
Using my Airspy's, the Source Audio window is much cleaner at 7.5 than 12.5. The RTL-SDRs quality difference is not as noticeable but still can be seen.

 

[mtindor]

Im am trying to decode Motortrbo audio from a local Mototrbo frequency 172.9500 using SDR# and DSD# software. Also installed is VB-Cable v.4.3
My antenna is connected to my computer (Win 8.1) with an RTL-SDR(USB) dongle.

In SDR#, the source is set to RTL-SDR(USB). Radio NFM, Bandwidth 10, no squelch. SDR# is tuned to 172.9500
Audio ...
Samplerate 48000 sample/sec.
Input: [MME] Microsoft Soun (the option to select is disabled, I can't seem to be able to change this);
Output: [MME] CABLE Input (VB-Audio Virtual Cable)

I have this frequency tuned into my scanner as well, so I know when a signal is being broadcast. WIth SDR# engaged, I can see the spike on the scope when a transmission is broadcast. I ***ume SDR# is getting the signal.

When I start DSDPlus.exe, the status window displays:
audio input device #1 = 'CABLE Output (VB-Audio Virtual '

audio output device #1 = 'Speakers (Realtek High Definiti'
audio output device #2 = 'CABLE Input (VB-Audio Virtual C'

audio input device #1 (CABLE Output (VB-Audio Virtual ) initialised
audio output device #1 (Speakers (Realtek High Definiti) initialised

I am not able to hear any decoded audio? DSD+ does not reflect any event log activity on the scope. Does my setup look correct? Has anyone any suggestions on why this may not be working?

I don't see any mention of your "Filter Audio" setting. Please make sure that "Filter Audio" is unchecked in SDRSharp. It defaults to being checked. And I can guarantee you will have no luck with most if not all digital decoding if you have "Filter Audio" enabled.

 

[rkillins]

Thank you all for your insight!!

Ubbe had the quickest and easiest solution. I changed the bandwith to 12500 and things started happening once a transmission was received. Sadly, all this effort for nothing as DSD+ revealed it was encrypted. Who would think a ski club would need encryption. >shrug<

MrLindstrome, I'm going to try and figure out what I need to do to eliminate SDR# as the signal source, relying solely on DSD+. A bit nervous, this is all so new!

I know very little about these new digital systems and forms, including Mototrbo (other than it's conventionally unmonitorable with a basic scanner). I was surprised having referred to DSD+'s activity window. It was one frequency, but two different talkgroups emerged. I'm only used to talkgroups being in multi-frequency trunked systems. How does that work?

 

[mtindor]

Thank you all for your insight!!

Ubbe had the quickest and easiest solution. I changed the bandwith to 12500 and things started happening once a transmission was received. Sadly, all this effort for nothing as DSD+ revealed it was encrypted. Who would think a ski club would need encryption. >shrug<

That's pretty uncharacteristic as 12500 is wide. It only need 7900. 10000 should have worked just was well (and actually even better than) 12500 for DMR. 7900 should work even better. But hey, whatever works for you.

 

[rkillins]

7900 works also.
At this bandwidth, DSD+ reported some additional information that wasn't reported at 12500.

Like :
Sync:+DMR
BS VOICE e:5r6m6r
BC VC2 e:7r6r6m
BS VC3 e:7r7r6r
Sync:+NXDN96 TS VOICE e:5r7r5r5m

At the top of the DSD+ window, S/S flickers between 4800 and 9600. P is predominently DMR but the odd time flickers with NDXN.

Is there anywhere I can reference to understand what I'm seeing in this DSD+ window?

 

[mtindor]

7900 works also.
At this bandwidth, DSD+ reported some additional information that wasn't reported at 12500.

Like :
Sync:+DMR
BS VOICE e:5r6m6r
BC VC2 e:7r6r6m
BS VC3 e:7r7r6r
Sync:+NXDN96 TS VOICE e:5r7r5r5m

At the top of the DSD+ window, S/S flickers between 4800 and 9600. P is predominently DMR but the odd time flickers with NDXN.

Is there anywhere I can reference to understand what I'm seeing in this DSD+ window?

Either you have multiple different signals on that signal (DMR and NXDN), or it isn't a very strong signal. The author may disagree, but in my experience you need around a 20 dB SNR (signal to noise ratio) or better to decode without errors. If it's a weak signal, or one being interfered with, you can often see DSDPlus attempting to figure out the sync pattern and showing DMR one moment, NXDN the next. No fault of DSDPlus.

the BS lines you'll typically see on encrypted traffic.

 

[slicerwizard]

I see no indication of encryption. How did the OP determine that? I just see multiple signs of poor decoding (maybe due to a lack of RF gain, maybe due to a poor antenna) and using SDR# instead of the tools DSD+ comes with, leading to what looks like a signal polarity issue.

 

[Ubbe]

7900 works also.
At this bandwidth, DSD+ reported some additional information that wasn't reported at 12500.

Like :
Sync:+DMR
BS VOICE e:5r6m6r
BC VC2 e:7r6r6m
BS VC3 e:7r7r6r
Sync:+NXDN96 TS VOICE e:5r7r5r5m

It cannot decode the signal properly at that narrow bandwidth as much of the information are then lost. You only see garbage info and not what are actually transmitted. Most DMR systems use NFM 12500 but there are few that uses supernarrow mode but yours are not one of those.

/Ubbe

 

[slicerwizard]

DMR transmitters do not broadcast 12.5 kHz wide carriers. Why do you keep insisting that?

 

[Ubbe]

The correct method are to use #SDR and adjust the banddwitdh so it just covers the whole signal. Then it doesn't matter if it is supposed to be one or the other value, it only uses what the transmitter are sending out and not extra noise or cutting out vital information.

/Ubbe

 

[rkillins]

I see no indication of encryption. How did the OP determine that? I just see multiple signs of poor decoding (maybe due to a lack of RF gain, maybe due to a poor antenna) and using SDR# instead of the tools DSD+ comes with, leading to what looks like a signal polarity issue.

Hi all. I'm only making the assumption that what transmissions are being received are encrypted because id the DSD+ Event Log I am seeing indicators such as:
Enc Group call; TG=11813 RID=255 Slot=2 Alg=BP 1s

If I do as Ubbe suggested in post#15, my bandwidth is reduced to 10,080kHz. I no longer am receiving the flickering between DMR and NXDN and 4800 and 9600 described in post #10.

I am the first to admit I don't have the greatest hardware for reception. Multiband scanner antenna hanging indoors on a relatively low power repeater signal. I cannot rule out errors as a result of dirty reception.

 

[dave3825]

I'm only making the assumption that what transmissions are being received are encrypted because id the DSD+ Event Log I am seeing indicators such as:
Enc Group call; TG=11813 RID=255 Slot=2 Alg=BP 1s

My fastlane displays some calls as enc when they are not and are clear comms. One of these days I am going to record same samples and email them to DSDPlus, or post here with a link for anyone interested..

 

[slicerwizard]

The correct method are to use #SDR and adjust the banddwitdh so it just covers the whole signal. Then it doesn't matter if it is supposed to be one or the other value, it only uses what the transmitter are sending out and not extra noise or cutting out vital information.

No, you're including spectrum where the signal is down at least 35 dB. That's just making the demodulated audio noisier.

Hi all. I'm only making the assumption that what transmissions are being received are encrypted because id the DSD+ Event Log I am seeing indicators such as:
Enc Group call; TG=11813 RID=255 Slot=2 Alg=BP 1s

Recording some raw audio in DSD+ and uploading it somewhere would help to get to the bottom of this.

Forcing DMR by adding -fr to the DSD+ command line will help your decodes when the signal is that noisy.

If I do as Ubbe suggested in post#15, my bandwidth is reduced to 10,080kHz. I no longer am receiving the flickering between DMR and NXDN and 4800 and 9600 described in post #10.

Yep, a quieter signal is helping the auto baud rate detection.

I am the first to admit I don't have the greatest hardware for reception. Multiband scanner antenna hanging indoors on a relatively low power repeater signal. I cannot rule out errors as a result of dirty reception.

The rtl-sdr.com dipole antenna can be tuned to any frequency of interest and can buy you 5 to 10 dB more SNR. It's a life saver.

Buy RTL-SDR Dongles (RTL2832U)