Some Basic DMR (MotoTRBO) Questions.

The place to discuss Commercial & Private licensed hand held & mobile transceivers, as well as imported hand held and mobile transceivers.
Post Reply
spynappels
Regular
Regular
Posts: 66
Joined: 01 Mar 2011, 09:18
Call Sign: 2I0SEH

Some Basic DMR (MotoTRBO) Questions.

Post by spynappels »

Hi All,

I have a question that's been puzzling me for a little while, since I've been decoding some MotoTRBO transmissions close to my work QTH using DSD+.

I've been told that DMR radios in general are easier on battery as they only are transmitting half the time when they're using 1 slot of the two available. While that might be a slight oversimplification, you get what I'm saying if we ignore the data packets with GPS data etc.

However, when I'm tuning around the section of the UHF spectrum where these signals are to be found, there is a very specific trace on the waterfall, even when no speech is being transmitted. This is seen by the masses of idle messages in the command line window, even when no voice is being decoded. Listening to SDR# also shows there is a digital signal being broadcast pretty much all the time.

My question is, where is this signal coming from? If the transceivers are not keyed up and transmitting either in slot one or two, what is generating the signal during idle times? Is it just that the transceivers are still generating some signals constantly but they are simply too short to have a meaningful impact on battery use, or is it something else, like perhaps some form of repeater? I'm not aware of any repeaters in use in the locations where I listen, but I guess that doesn't mean there isn't one (or more).

If it is the case that the repeater is constantly transmitting, they must be amazingly engineered pieces of equipment, able to withstand an approximately 100% transmit duty cycle. Also, if some purely portable handheld transceivers are being used, with no repeater, does that mean that the characteristic sound of a DMR signal is only heard sporadically, while one of the transceivers is actually transmitting?

Sorry if these seem like simple questions, I'm a simple person.

Regards,
Stefan
User avatar
FakeJake
Radio Addict
Radio Addict
Posts: 879
Joined: 21 May 2011, 22:08
Call Sign: 2E0SEY
Location: Saltney, Chester IO83me

Re: Some Basic DMR (MotoTRBO) Questions.

Post by FakeJake »

It'll be a repeater. Possibly on a high building or buildings
Jake 2E0SEY
Saltney, near Chester (Cheshire-Flintshire border)
Monitoring 2m simplex (when I can)
Dysgwr Cymraeg
User avatar
radiosification
Top Poster
Top Poster
Posts: 2495
Joined: 27 Dec 2010, 23:52
Location: London
Contact:

Re: Some Basic DMR (MotoTRBO) Questions.

Post by radiosification »

Yes what you are listening to is most likely repeaters. If you listen to the actual transmission from the radio in analog, it doesn't sound anything like the repeaters and on the waterfall you see it turning on and off. Have a look and see if you get anything on repeater inputs or UK simple business radio frequencies (although these will have analog on too)
Repeaters idle by themselves at a set interval. I don't know exactly why this is, but it is useful in some things such as when using roaming with IP site connect.
Close to 100% duty cycle is common on these DMR repeaters when used for data applications. For Tier 3 which is DMR trunking you have a dedicated control channel which transmits all the time.
If you're interested in digital voice, check out my YouTube channel:
http://www.youtube.com/radiosification
spynappels
Regular
Regular
Posts: 66
Joined: 01 Mar 2011, 09:18
Call Sign: 2I0SEH

Re: Some Basic DMR (MotoTRBO) Questions.

Post by spynappels »

Thanks for the responses guys. That makes things a little clearer, I guess it also explains why I hear two different conversations, one in each ear, as only a repeater should have audio (or any other data) in both slots.

Thanks again, DMR is a fascinating area and I'll look forward to learning and experimenting more with it.
User avatar
radiosification
Top Poster
Top Poster
Posts: 2495
Joined: 27 Dec 2010, 23:52
Location: London
Contact:

Re: Some Basic DMR (MotoTRBO) Questions.

Post by radiosification »

Have a look through my YouTube channel and blog. I have a lot of stuff on DMR which might be useful to you. Most particularly this stuff:

Fast forward a bit to around 6 minutes in this video and you'll see someone operating in simplex/on the repeater input.
https://www.youtube.com/watch?v=sPrSyfu_nvg

And on the front page of my blog at the moment, try using DMRdecode and WinDSD to get more information on the systems you are listening to. DMRdecode doesn't decode voice, just other data and signalling. WinDSD does both voice and other data and signalling.
http://radiosification.blogspot.com/
If you're interested in digital voice, check out my YouTube channel:
http://www.youtube.com/radiosification
spynappels
Regular
Regular
Posts: 66
Joined: 01 Mar 2011, 09:18
Call Sign: 2I0SEH

Re: Some Basic DMR (MotoTRBO) Questions.

Post by spynappels »

Thanks for that, based on the samples in your Youtube video, I was in fact listening to a repeater output rather than simplex DMR or a repeater input. Your explanation makes perfect sense and it also makes sense that simplex is more difficult for DSD+ to decode as it isn't getting a steady signal but rather a stop/start signal which is probably more taxing to react to and filter the useful data out of.

Subscribed to the channel, I think that may be useful for future reference too.
superdave
Super Member
Super Member
Posts: 370
Joined: 08 Jul 2012, 20:10
Call Sign: M6JXP

Re: Some Basic DMR (MotoTRBO) Questions.

Post by superdave »

The repeaters are basically constantly transmitting even in idle. Also remember that the radios can send much more data than just voice, for example GPS, text messages, radio checks etc.

When you are using a handheld/mobile on a repeater channel, and you key up, the radio first sends some packets to check whether it's actually in range of the repeater as it won't TX if it isn't.

It's true that DMR will use less battery than analogue as it's only transmitting half of the time. This is one of the main advantages of it.

The Motorola DR3000 repeater is rated to 100% continuous full duty cycle at 40W.
User avatar
wheelbarrow
Regular
Regular
Posts: 55
Joined: 11 Apr 2013, 20:58

Re: Some Basic DMR (MotoTRBO) Questions.

Post by wheelbarrow »

Don't forget that analogue MPT trunking systems have a dedicated control channel too which is transmitting at 100% of the time, some systems would scroll control between channels to give each repeater a break and some had 1 dedicated control channel.

As for improved battery life battery on DMR radios, well maybe, but the typical Motorola DMR radio battery still lasts about the same time vs their analogue radios so I suspect that while DMR is only transmitting 50% of the time compared to an analogue radio, the digital circuitry/components used are more power hungry so probably explains why we don't see DMR portables with 24 hour battery life.
spynappels
Regular
Regular
Posts: 66
Joined: 01 Mar 2011, 09:18
Call Sign: 2I0SEH

Re: Some Basic DMR (MotoTRBO) Questions.

Post by spynappels »

I suspect that if encryption is used, battery life will suffer. In my experience with servers running various forms of encryption, it does have an affect on the power consumption, so I'd guess that would also be true for battery powered devices.
User avatar
wheelbarrow
Regular
Regular
Posts: 55
Joined: 11 Apr 2013, 20:58

Re: Some Basic DMR (MotoTRBO) Questions.

Post by wheelbarrow »

Basic encryption is very basic, just a small digit number that seems to be more an access code than any real encryption method, but certainly more advanced encryption could add some slight battery drain on processing the voice (well something has to make it sound a bit worse after all!) :D
User avatar
radiosification
Top Poster
Top Poster
Posts: 2495
Joined: 27 Dec 2010, 23:52
Location: London
Contact:

Re: Some Basic DMR (MotoTRBO) Questions.

Post by radiosification »

Basic encryption is pretty effective at stopping people from listening in. Radios from other manufacturers can't decrypt it, neither can DSD or DSDplus. It would take at least few hours to find a random basic privacy code when doing it the only way I know - guessing a code, programming it to the radio, then seeing if it works. When combined with RAS, which stops other radios from even listening to the repeater output, and therefore being able to guess the code, it turns out to be an effective stop on eavesdropping.
Now obviously it isn't actually secure. Someone could write a piece of software that could guess the code, but right now, there's nothing like this available. So, its effective for use in applications where it wouldn't be dangerous to life or property if people do listen in.
If you're interested in digital voice, check out my YouTube channel:
http://www.youtube.com/radiosification
User avatar
wheelbarrow
Regular
Regular
Posts: 55
Joined: 11 Apr 2013, 20:58

Re: Some Basic DMR (MotoTRBO) Questions.

Post by wheelbarrow »

Absolutely, what I was referring to was that the basic encryption method is unlikely to affect battery drain as there's very little encrypt/decrpt for the radio to do in addition to the usual data to be processed.

Basic encryption and RAS will certainly keep most people from evesdropping unless they're very persistent.

Enhanced encryption on TRBO appears to reduce voice quality slightly, compared to basic or none, especialy on the fringe. Not tried AES yet so can't comment on that. RAS doesn't appear to have any noticable impact when used.
User avatar
radiosification
Top Poster
Top Poster
Posts: 2495
Joined: 27 Dec 2010, 23:52
Location: London
Contact:

Re: Some Basic DMR (MotoTRBO) Questions.

Post by radiosification »

RAS isn't meant to, basic and AES aren't meant to either, but enhanced is meant to slightly reduce voice quality.
If you're interested in digital voice, check out my YouTube channel:
http://www.youtube.com/radiosification
User avatar
bigbloke
Top Poster
Top Poster
Posts: 1449
Joined: 25 Aug 2008, 17:53
Location: Nominally Newport (South Wales) but potentially "anywhere"
Contact:

Re: Some Basic DMR (MotoTRBO) Questions.

Post by bigbloke »

lets try and close the gap on this one...

when you listen to DMR with DSD+ you will note one of two types of burst formation:

1) conversation <long pause (1 min)> burst <long pause (1 min)> conversation

2) conversation <1 sec pause> burst <1 sec pause> burst <1 sec pause>conversation


the purpose of 1) is to keep all radios in sync with the repeater and ensure when the
next conversation starts, all radios will break squelch at the same time and hear the full
conversation. This occurs, typically, on a single frequency repeater system- i.e. one
repeater within the DMR network.

when you hear scenario 2) you should notice the words "CAP+" appear in the bottom corner
of the DSD+ event window. these 1 second interval bursts tell the radio which channel is the
"rest channel" i.e. the one they should be listening to to determine which of the repeaters in the system will host their next conversation

the other scenario is where you have lots of LRRP location data or ARS requests - these can fill up the radio channel quite significantly. you will see the purple text in the event window

regards

BB
Post Reply