DSD and -DMR versus +DMR

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w4rtt

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What does it mean when you get -DMR instead of +DMR at the beginning of each line?
I have a single channel here that runs DMR, and the entire transmission shows as -DMR slot 1 BS DATA.
If I switch to the input frequency, I get +DMR slot 1 BS VCX and it will decode the transmission.
 
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br0adband

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- and + represent the polarity of the given system, as I understand it (not quite the same as antenna polarity or electrical, so that's all I can say).

The BS DATA means it's transmitting pure data (DATA) from the base station (BS) to the field units which could be text messages or other related info - it can also indicate a private/encryption transmission for a given group on DMR as I understand how it works. DMRDecode would be able to identify encrypted or non-encrypted comms by denoting it as "private," iirc. I don't use DMRDecode much anymore, it's nice to have but for me it doesn't actually do much in my usage.

The BS VCX means it's transmitting voice channel audio (VCX) from the base station (BS) to the field units and that is what DSD/DSD+ is capable of decoding.

It's entirely possible to have something like BS DATA on slot 1 while having BS VCX on slot 2 since DMR/MOTOTRBO is a 2-slot TDMA based form of digital communication meaning it can send out both types of signals at the same time across the same frequency. Pretty neat stuff, actually.

DSD+ detects the given polarity automagically for such signals so it's not something you have to bother with while the older DSD (iirc, I haven't used it in quite some time) required you to specify positive or negative DMR polarity or else the decodes would be complete gibberish, more or less.
 

w4rtt

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Here's a twist on this system.
Again, monitoring the input frequency. I have been getting these transmissions.
NXDN96 CB VOICE
NXDN96 MB VOICE

DSD attempted to decode the audio, but the signal was too weak.

During these transmissions, nothing is heard in the output.

Can this single channel be both MotoTRBO and Nexedge?
 
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racingfan360

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Randy

Are you sure it said NXDN96 MB and not NXIDAS MB ?

For me it is not uncommon to get a few packets decoding in error for a NXDN48 or NXDN96 signal showing as a NXIDAS. As your signal is weak that will increase the chances of errors in decode.

>Can this single channel be both MotoTRBO and Nexedge?
I'd say it's highly unlikely someone will implement both systems together (think of the cost), but it's not unusual to have some frequencies assigned to multiple users and they independently decide to implement different technologies.

I think the weak signal is your main issue.

Jim
 

w4rtt

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Randy

Are you sure it said NXDN96 MB and not NXIDAS MB ?

For me it is not uncommon to get a few packets decoding in error for a NXDN48 or NXDN96 signal showing as a NXIDAS. As your signal is weak that will increase the chances of errors in decode.

I think the weak signal is your main issue.

Jim
Here is a screenshot.
 

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br0adband

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It's DMR and it's a bad signal, not NXDN. If it wasn't DMR I doubt seriously you'd ever pull a color code from it several times in succession and it be a match - yes it shows 4 and 2 and 6 but it shows CC=1 more often than not so that's my guess.

If you have to know for sure and you're trying to decode it as DMR then just start DSD+ using the -fr switch and see if that helps. If you can't improve the quality of the reception/signal, it might be possible to get something useful from using dsdtune to eek out the best performance from what you are getting - there are other threads describing how to make the best use of that tool in addition to DSD+.

Also, your volume matters a great deal as well - having a 100% level (as shown in your posted image) is not always the best solution, it can even hurt decoding performance more often than not, especially on a weak signal full of distortion and crackling because you're sending it full force to the decoder. Try adjusting to get a level between 60 and 80% and see how that fares. DSD+ does wonders with weak signals by default, and using dsdtune can improve things dramatically in certain situations but there's still a lot you can do to improve things.

And of course you can always check the FCC database for a given frequency then dig into the actual transmissions it's licensed for on a given frequency: if it's licensed for DMR then that's what you'll find on it, likewise with NXDN content (they have different transmission identifiers).

Good luck...
 

br0adband

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The emission type is 7K60FXE
Which is DMR/MOTOTRBO as expected - outside the US it's typically referred to as DMR which should the accurate nomenclature for it; Motorola's variant is known as MOTOTRBO:

Code:
Emission designators for MOTOTRBO: 7K60FXE (voice), 7K60FXD (data).
 
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