DMR question

[Tim-B]

When monitoring the frequencies of a local communications company that rents radios to local businesses for use on the comm company's repeater I noticed that many DMR transmissions stay muted while others have good audio. I thought it was maybe a problem in the way that I programmed by scanner but I noticed the same thing happened with multiple scanners and also an Alinco DJ-MD5 business radio in promiscuous mode and also when monitoring those same frequencies with SDR# with the Simple DMR plugin. When using all DMR capable scanners I own, and the Alinco, and airspy/DMR#/Simple DMR at the same time I noticed that either they will all recieve the transmission with no problem or all of them will stay muted at the same time when there is a transmission. So my question is - are these encrypted DMR transmisisons where the audio stays silent? If so then why does my Uniden 436HP not say "enc" on the display or is the 436 not able to tell if a DMR transmission is encrypted?

 

[Whiskey3JMC]

DSDPlus would definitely tell you if the frequencies are encrypted, though so should your 436HP if you're held on the frequency. Are you running the latest firmware on the 436HP?

 

[RaleighGuy]

One possibility is the DMR tail I notice many times on a system if you don't have it programmed properly with slot/cc, but that is just a guess.

 

[Tim-B]

As far as I know I have the latest firmware for the 436. I tried to log into the myuniden.com website where I used to purchase upgrades and such so I could get the NXDN upgrade and it always redirected my somewhere else as if that site no longer exists. The transmissions where it remains silent are usually between 5 to 10 seconds long just like you would expect from a voice transmission. The most commonly used frequency for that company's repeater also constantly transmits very short data bursts about two seconds apart where there is no voice traffic if that gives a clue as to what type of system this is. I have also noticed that on the silent transmissions the slot number alternates back and forth between 1 and 2 as if the scanner is confused. Color code 5 keeps coming up on those transmissions as well. Color code 5 also comes up on the short data bursts that occur every two seconds. Could these longer transmissions just be data and that is why there is no voice?

 

[sonm10]

Data bursts?

 

[Tim-B]

Well, OK. After I started to pay better attention I noticed a pattern. Now it looks like these are not voice communicaitons that I am missing but they are something automated. I watched the waterfall display and there is a regular pattern that repeats. There nine short burst transmissions that last less than half a second each spaced a little more than two seconds apart followed by a longer silent transmission lasting seven seconds then the cycle repeats over and over. When someone transmits it interrupts the cycle and it starts over after the person ends his transmission.
@sonm10 - by data bursts I mean very short transmissions that sound like a quick squelch tail on airspy/SDR# but are silent on scanners. I was assuming they were just data. When the seven second transmission happens it is always color code 5 and the slot number wobbles back and forth between 1 and 2.

 

[sonm10]

Data bursts will be ignored by scanners - could be LRRP or other data

 

[slicerwizard]

This is not the first time (nor will it be the last...) that a query like this comes up. The free version of DSD+ (plus a $20 dongle) will show you what those transmissions are and it'll let you make recordings of those transmissions so others can tell you what they are. That's my advice for anyone who wants to lift the veil on DMR or NXDN signals.

 

[lu81fitter]

Does the system have more than 1 tower or site that is used as a repeater? The system local to me has 5 sites/towers. The towers put out a "burst" so any scanning portable radio can lock on to the closest tower for use. Maybe that is what's going on. I know the process is probably much more in depth then how I explained it, but that's how it was explained to me. Maybe some of the experts here can either confirm or correct my statements.

 

[jaspence]

The Alinco is a decent DMR radio, but not in the same league as a true commercial model. Some reports claim it is based on the same platform as the Anytone and BTech DMR radios, which are also better than the 3rd tier CCRs but still not in the Motorola or even previous Hytera radios class.

 

[racingfan360]

Probably a MotoTRBO Capacity Plus system's Rest Channel, which can be identified by the rapid "Beacon" data burst approximately every 2 seconds. As slizerwizard says, get yourself DSD+ to tell you the full details.

 

[mikewazowski]

Data bursts will be ignored by scanners - could be LRRP or other data

Not Uniden scanners. They’ll happily sit on a channel that has nothing but LRRP bursts on the second timeslot when programmed as a conventional channel.

 

[sonm10]

Not Uniden scanners. They’ll happily sit on a channel that has nothing but LRRP bursts on the second timeslot when programmed as a conventional channel.

Not an issue if program as one-freq trunk

 

[Tim-B]

Thanks guys for the replies. At this point I am not much worried about what the data transmissions are for. I am just glad that I am hearing the voice transmission. I originally thought I was missing a lot of transmissions when the seven second long transmissions were happening. After I watched them for a while in SDR# I realized that it was something automated in the system. After listening all day I realize now that I am hearing all the replies to transmissions.

 

[mikewazowski]

Not an issue if program as one-freq trunk

Which makes the GPS feature of the scanner useless if you’re travelling. You’d have to figure out every DMR conventional channel within range of your journey and convert them into one frequency trunk systems. Or you just lock out every frequency with data as you travel and potentially miss something.

 

[Ubbe]

There nine short burst transmissions that last less than half a second each spaced a little more than two seconds apart followed by a longer silent transmission lasting seven seconds then the cycle repeats over and over. When someone transmits it interrupts the cycle and it starts over after the person ends his transmission.

That could had been the automatic ID transmission of the license number in morse code, but that are sent in analog.

When the seven second transmission happens it is always color code 5 and the slot number wobbles back and forth between 1 and 2.

If it wobbles between slot 1 and 2 then it is acting very strange, as if it is searching for the control channel data or the control data are sending the scanner to the voice slot but there's no valid voice data there and it goes back to the control channel slot and repeats.

If you have programmed it as trunked, I guess it now are a OFT, and you have the voice channels LCN incorrectly set to that same frequency as the control channel, when it should actually be set to another frequency, then it would wobble between the time slots.

/Ubbe