Saturday, November 14, 2015

DMR Likes and Dislikes

I recently eluded to that I have been playing with DMR.

I helped get one going locally.  And the only real reason I did that was to learn a bit about it.  Heck I don't even own a radio.  But a friend was nice enough to give me a Motorola XPR-6550 loaner.

I like the TDMA part.  To me it's truly digital.  Everything else that I have played with seems like digital audio on a FM modulator.

The XPR has nice loud digital audio out of it.  You'd expect this from a Motorola.  The audio coming out of my IC-92 for D-Star was never loud enough unless you were in a quite room.   The digital audio out of the XPR sounds really good.  This is because it uses the AMBE+2 vocoder, and a better sample rate than D-Star.   Motorola products do post vocoder DSP.  I have a recent DSP firmware in the radio (and yeah that is upgradable).  It sounds better than D-Star on the IC-92, and sounds better than P25 that I was doing with an old mid-90's Motorola Astro Saber (old DSP firmware in that).  I have an XTS-2500 that I listen to the County Police on, and while this XPR DMR radio is close in quality, I still say the XTS-2500 sounds better. The XPR doesn't go R2D2 like the IC-92 when people get into a crappy signal situation.  It mutes.

I like that you don't have to buy Motorola to use it, there are plenty of DMR radio options, like Connect Systems, and a very reasonable option at that.  Which is good because while I like Motorola, their software and customer service is a night mare on all accounts.

DMR wasn't custom made for ham radio, so you can't put your callsign into the radio like D-Star.  Each DMR radio uses a numerical identifier.  You can create alias/contact lists in your radio, so that when my DMR- MARC id of 3155089 is transmit, it shows as KB9MWR on your radio.  So the contact list thing can get to be big on a network.

When my friend was first trying to get my interest in DMR he kind of emphasized the DMR apps.   There are several ham DMR projects on github, but all of them are for the infrastructure.  In all honesty I am not sure what one would write for the end user app wise.  Maybe extend D-Rats support to DMR?  There are number of application development documents available to developers from Motorola, if you can get your hands on them.

Programming the radio's is pretty confusing  There are pre-made code plugs however.  I do like how when you connect the XPR-6550 programming cable to your PC it comes up as an ethernet interface.  And yes you can run wireshark on it.

Texting (sadly the DMR networks don't really do much with this part) is much better than with the IC-92.  On the IC-92, you had to dial in each character (possible 26+ dial clicks) and hit select when the character was the one you want... rinse, repeat, etc.  With the XPR-6550 and CSI radios, its like a T9 telephone keypad.

You can have a private call on DMR.  (Though discouraged on the network) This is unlike most of ham radio where you have a carrier squelch receive option.  With DMR, there is no listen to all traffic on the channel.  You have to specifically program talkgroups you want to hear, etc.  I never really figured out how to callsign squelch on D-Star.  So at least on DMR, you don't have to listen to everyone just to keep an ear out for your buddy, etc.

The repeater (XPR-8300/8400) is still basically two mobiles in a box like D-Star.   The engineering is better however. The repeater has a network jack in the back.  I like that I don't have to be the Linux systems admin or have a computer at a remote site.  Though hack/adaptability is more likely with the latter.  Network connectivity to the repeater is stateful, so it doesn't require any port forwarding.

Repeaters can be had for next to nothing on a promotional/regional basis like how D-Star got started.  In this case, there are two Motorola engineers that are competing to build networks, that don't appear to have any real backing a higher level.  One network is DMR-MARC, the other DCI.  Both have restrictive rules like the main D-Star network about linking to other things, etc.  Like with D-Star people grew tired of the network rules and began to roll their own network that is more friendly to experimenters, for DMR it appears to be DMRX/BrandMeister.

Even with two time slots, with all the remote/linked talkgroups you some times wonder if two slot TDMA is enough. When things get busy a radio "Bonk" is common to come back when you go to transmit, indicating that time slot is busy.

The XPR-6550 has a GPS built in.  In my other DMR post, I show how this can be bridged to the APRS network.  I like that.  I never did buy the uber expensive GPS microphone for the IC-92.  So far I haven't spotted a cheap non Motorola DMR radio with GPS. 

So what is the lure to the end user?  I guess that would be radio manufacture choice, and less R2D2.  The radio options are commercial, and some (CSI ones) are somewhat field programmable.  There are no-dual band ones yet.  The other lure might be that you use DMR at work as its pretty common, so you are used to it etc.

So far I haven't heard more interesting conversations than I have else where.  Call me strange but I really don't give a crap about having some over priced toys that lets you talk to other people. I can do that with analog, or no gear at all. I am here to try and learn something.

I am not sure if I'll buy a radio.  It's really a matter of if it actually takes off in my area.