Please tell me about DMR

Discussion in 'Amateur Radio General Discussion' started by Tony, Nov 2, 2016.

  1. Tony

    Tony Moderator Staff Member

    Does anybody here work DMR?

    What is the value of it? Is it only for local, or can you "dial up" a distant friend?

    I'd love to get into it, but we don't have it here.
     
    wedgar likes this.
  2. wedgar

    wedgar Administrator Staff Member Gold Member

    I have not used it. I'd try calling ARRL at 860-594-0200 and see if someone in the lab could help you learn a little more.
     
  3. W.T. Jones

    W.T. Jones Moderator Staff Member Silver Member Golden GPS Recipient AtlDiv EPA Leader AtlDiv ARES Member

    OK, since I am now going to be delving into the world of DMR I'll give it a shot at explaining at least what I know.

    Here goes....

    DMR is based on a Motorola Protocol called Mototrbo (pronunced moto turbo) that encodes audio over the air to the repeater (tier 1) and to the repeater network (tier 2) that connects the repeater with the network.

    On the user side - Each user (world wide) must have a unique ID assigned that is programmed into his radio. To avoid being called names I am using "his" to represent the Amateur Radio Operator which might be a his or a her to save typing. You can accuse me of being lazy. How does one get this ID. It is pretty darn easy actually. Go to this web site:

    http://www.dmr-marc.net/

    This site is the big dawg on the block. There are apparently others but in this neck of the world this is where to play.

    The id that you get is programmed into your DMR equipment and identifies you to the DMR network. I guess you could think of it like the IP address that you computer gets so that it can communicate on the Internet.

    The equipment for the user is not all that expensive. Tytera makes one called the MD-380 which runs for about $110. The newer version is the MD-390 which is slightly more and I will probably spring for that one.

    https://www.amazon.com/TYT-MD-380-Moto-TRBO-Radio/dp/B00X6FYWWS

    These radios also do analog FM very well too so you can use them on your FM repeaters.

    Operationally there isn't much difference from operating on analog FM except that you join what is called a Talk Group. The repeater has "time slices" allotted for each talk group. You key up, talk, and the repeater determines what talk group you are in and sends the digitized audio to that group. So it comes out locally but if you have someone logged into your talk group on another DMR repeater it comes out there as well. Your radio holds the transmission until the appropriate time and sends it so talking over one another is pretty much non-existent.

    The repeaters are linked by Internet to a master repeater. The one around here is in NJ. It is called a C-Bridge.
    Here is a link to the one in NJ's web site: http://n2jti.net/

    BTW, these talk groups are local, regional, national, and international. DMR seems to be all over the world right now.

    It is not like D-Star but it is like D-Star. You need to register but compared to D-Star the registration process is pretty painless. It is digital and shares much of the characteristics of any digital radio. It is not like Yaesu Fusion in that there is no central control like D-Star or DMR on the Fusion system.

    BTW, if the network goes down the local repeater still functions.

    The repeaters are complex but then again what repeaters are not complex. There is a the addition of the PC to talk to the network and make it happen. That shares the same similarity with the Echolink, Allstar, IRLP, and other linked repeaters. The difference is the audio is digitized in your handie talkie. There is a lot packed into the chip.

    You can watch the activity on the repeaters at this link: http://netwatch.n2jti.net/

    It is still confusing to me but basics are the repeater indicates red then it is transmitting to the user. If it is green the user is transmitting into the repeater which goes to the C-Bridge for distribution if necessary. From what I understand you can join talk groups for many purposes. If you want to stay in touch locally you join your local talk group and your digitized audio is routed back to your home repeater or what ever repeater is part of the talk group. If you want to talk to someone in the Netherlands then join the international talk group.

    Now there are things that I don't understand like color codes which I think refer to the time slots on the repeater but that remains to be understand by yours truly. There will be more to come on this but I am only scratching the surface. After Thanksgiving I will get with Mark, N3MBK, our local DMR repeater owner for a programming session. When that is done I'll have more.

    Right now I have been playing with the FT2D Yaesu fusion HT and I have to say that I am very impressed by the little radio. On digital there is almost no signal from the repeater but the audio is full and robust both ways. I am waiting to see how the DMR compares to it. This going to be an interesting experiment.
     
    wedgar likes this.
  4. Tony

    Tony Moderator Staff Member

    Thanks, WT. That helps.

    I have been reading some, but hams in general who write about this so far are doing a terrible job eexplaining clearly. Yours has been the best. Bravo. Others are filled with jargon and assume we have knowledge of DMR already.

    The link you sent displays poorly on my iPad. It blows each side off the screen, and the red and gree you mention doesn't apppear. I will have to research to see what I'm doing wrong.

    The website says it's for PA, but it must mean the eastern PA tri-state because it only goes to Hershey, not here in western PA.

    Does this system mean that from PA I could join, say, a Cincinnati talk group and chat with a friend there?

    Wonder what the good and bad is about using a proptietary Motorola underpinning?

    This whole digital realm has presented a block to my entering it. First there is nothing digital here in northwest PA that I can easily find. Next is what system to use. I first heard of Dstar, and was ready to try. It is non-proprietary and is in Icom. Then I saw Fusion come along. It's on Yeaseu and won't talk to Dstar. And now DMR is proprietary from a brand that is really not used heavily by most amateurs. An excellent brand, for sure, but it won't talk to the other two.

    It looks like I will be watching the side-show for a while and waiting for the egos and politics to settle. Check the activity between some national DMR body and the Pacific Northwest, which just withdrew front the national group. Check www.trbo.org for a look at that. My goodness. Hams dropping national connects for whatever reason is counter to our mission.
     
    W.T. Jones likes this.
  5. W.T. Jones

    W.T. Jones Moderator Staff Member Silver Member Golden GPS Recipient AtlDiv EPA Leader AtlDiv ARES Member

    Tony,

    I took some time and reviewed the info on the www.trbo.org web site.

    (Insert deep sigh here!)

    I cannot say that I am surprised to see this kind of thing. I know that where there are lawyers there will be lawsuits. It is the way of our society.

    It is without any doubt a sad situation. I don't know who is at fault, who is right or wrong, or who in the legal system has the knowledge to decide what should be done.

    This is one reason why, as a person who is charged with planning emergency communications, I will not consider these systems as reliable to the point where they can be used for emergencies. Casual conversations? Absolutely. Putting my money where some one else's mouth is doesn't make sense.

    The high and lofty statements made by repeater owners (and the owners of the underlying infrastructure) can be reversed because the statement maker gets up on the wrong side of the bed one morning. Where does that leave those of us who have put our proverbial eggs in that proverbial basket. Holding a particularly messy basket full of broken eggs is where.

    I will continue my quest to use DMR because the entry costs are minimal and it looks like fun at least locally.

    My statements to all those planning for disaster related communications has been "if you don't own it then don't rely on it."

    You may not own the repeaters
    You may not own the site
    You may not own the road to the site
    You may not own the power supply to the site
    You certainly don't own the Internet
    A piece of ice comes down off the tower and smashes the house where the repeater is located. We certainly cannot control acts of nature. (been there with that one.)

    It is all so fragile. It works well and it is a great thing but Amateur Radio is not the government nor is it Corporate America.

    The owners of the repeaters grow old and want to get away from those trips to the mountain.
    Their finances change and they cannot afford to own a repeater.
    The party that owns the site sells it and the new owner does not want Amateurs on his mountain.

    I have seen all that and I have seen the disgruntled guy get banned from the repeater and run to his lawyer.

    So from an emergency standpoint I have to do a careful analysis of the resources and those controlling the resources. At times it comes down to the point of saying no to what appears to be a great thing. I catch heat from all concerned about it. It is just the normal reaction of those who see the fun technical part but have no foresight as to the consequences.

    But for the fun of it I am going to go digital and see what kind of fun I can have. Is there much difference between talking using Analog FM and Fusion. Not really but it is furthering my interest in Amateur Radio. I will try DMR because it seems interesting but having a C-Bridge in NJ that is the single point of failure for the system means that it is not something that prudence says rely on for disasters. The good man who owns that C-Bridge may find that he is cut off from the rest of the world by another Hurricane Sandy. He can do nothing about that even though his site may survive his Internet links may be severed.

    It is the same with things like Allstar networks and Echolink. Nice tools and if I reach into the toolbox and they are working I'll find a use for them. But you can be sure I'll have a backup for them.

    I was in a situation like you. No digital resources to try. Now I have Fusion and DMR. I have several Fusion radios courtesy of the County of Luzerne. One of our Amateurs has put up a Fusion repeater so it makes sense to try it. The nice thing about Fusion is that it will do either C4FM or Analog FM. (BTW, that choice alone makes Fusion seem more sensible to me) and it doesn't rely on any underlying network to function. The DMR repeater looks interesting and if it works as advertised I will be happy. If it doesn't my investment is relatively small.

    I guess I should tell you what I rely on as far as repeaters. Simple. One that is on Red Rock Mountain in a very secure site provided by the State of PA with emergency backup and has a coverage area of 8 counties. The other is located in a similar site on the other side of the county with similar coverage. The owners, and the fact that it is owners is a big difference, signed agreements for the use of their repeaters and guarantee a line of succession including turning them over to the County for a suitable price. The equipment is top shelf commercial equipment and professionally installed. These two repeaters have the same quality that any law enforcement repeater system would have. It is as close to being "mine" as I could make it. Even access to the sites is controlled to the point that visual ID via camera must be made before access is granted. It is a good system.

    I'll let you know how the DMR works in a week or so. It really does look like it will be a fun system to operate on.
     
    wedgar and Tony like this.
  6. wedgar

    wedgar Administrator Staff Member Gold Member

    Yes, it made it much easier to understand for me.

    I'd be interested but find no repeater near Savannah, GA nor Bradford, PA. Guess I'd have to wait until it becomes a little more popular in these areas before buying one.

    The entry price isn't that bad either - about $110-
     
    W.T. Jones likes this.
  7. W.T. Jones

    W.T. Jones Moderator Staff Member Silver Member Golden GPS Recipient AtlDiv EPA Leader AtlDiv ARES Member

    That lack of a repeater that does a digital function is without a doubt a major stumbling block.

    I just put an APRS digipeater on Forkston Mountain overlooking Tunkhannock. It was a simple job because there are no duplexers, no multiple antennas, no controllers other than the digi. But like other modes APRS gets over looked. I had the opportunity to do it so I did it. Now I can get an APRS message from the Luzerne County EOC to the Wyoming County EOC in a second. It is like an SMS message but it is more reliable than email. It is good for quick updates.

    Getting acceptance of something as easy as APRS is extremely hard. Getting old guys who think analog FM is the only way to go is even harder since they control the current repeater crop. Time may change that.
     
    wedgar likes this.
  8. wedgar

    wedgar Administrator Staff Member Gold Member

    Yup, we just get comfortable and don't want those new fangled things coming in we don't understand...

    In our area, we had a repeater trustee that just didn't want one of those new-fangled auto-patches on the repeater.

    So - for the fun of it, some of us where in a city that had an auto-patch and having privileges on the auto-patch, we recorded an autopatch conversation held on that repeater.

    Then when back home, played back the recording of the auto-patch.

    The trustee made a very quick trip up to the repeater he was the trustee for to see who/what changes were made on "his" repeater. <GRIN>
     
  9. Tony

    Tony Moderator Staff Member

    You always can count on wedgar! :p
     
  10. Jeremy

    Jeremy Active Member

    My little addition to this: The DMR radios are based on commercial user interface as well. The typical ham display with frequency and lots of buttons will be missing for the most part. My DMR radio has a small screen, but it doesn't give the frequency. I set the repeater via menu, then use the 16-position dial to set which talk group I am using. The programming has to be done with a computer for most of the hardware, and it can get a bit confusing with all of the options.

    I don't find the audio all that great, it sounds very digital, but I don't have much to compare it to. My H-t is a bit out of range for the Scranton, PA repeater, so I have only used it on CT machines when visiting my parents or simplex.
     
    wedgar likes this.
  11. Tony

    Tony Moderator Staff Member

    I have a friend in Cincinnati who has one, and I think. There is a repeater there. I should go visit for demo.
     
  12. wedgar

    wedgar Administrator Staff Member Gold Member

    Thanks for your comments... Perhaps waiting until the technology improves might be worth it?
     

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