DMR Article by Matthew Littleton, KN4SWB

What’s All This Talk About MotoTrbo?

By: Matthew Littleton KN4SWB

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Have you heard anybody talk about digital communications on 2 meters or 440 lately? If so, it has more than likely been discussion over four of the more popular modes known as DSTAR, Project 25 (P25), Yaesu’s System Fusion, or DMR (Digital Mobile Radio also referred to MotoTrbo). At the winter SERA meeting in Pigeon Forge, TN, I was fortunate enough to spend some time discussing DMR with several of the Directors and Vice Directors and answer questions about DMR. As I sat through the winter meeting, it occurred to me that maybe many of you have questions about DMR, but you are just not sure who to ask. I am by no means an expert. However, I have been blessed with some great opportunities to learn about emerging technologies. This article is not intended to suggest that DMR is any more or less advantageous over any other technologies. However, as amateur radio professionals, we should always find ourselves looking for new and innovative ways to communicate. DMR, like the other digital technologies, is a new and emerging technology. I often refer to multiple communications technologies as tools in our tool box. No one tool in your tool box at home can do every job just as no one communications method, band, or system can work in every circumstance.

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Before we begin, I did not stay at a Holiday Inn Express last night, but I am charged with overseeing roughly $15 million worth of communications infrastructure including business/industrial, public safety, and amateur radio systems. I am a Captain and Deputy Emergency Manager for Anderson County in South Carolina where I also serve as the South Carolina Vice-Director for SERA, Southeastern Repeater Association. We are fortunate to have a great team of professionals who maintain these systems, learn about new technologies, and guide our customers (other agencies) in migration paths. They are Richard Donald (AE4PZ), Jeremy Miller (KI4TZZ), and James Culbertson (KJ4VLT).

DMR

Digital Mobile Radio which stands for, DMR was developed by the European Technology Standards Institute (ETSI) in 2005 and is the standard for, professional mobile radio (PMR) users. The interesting thing to me is this is the first time that I can find an instance where the users drove the manufacturers by telling the manufacturers we want it to have these features and cost this much. This idea alone is how communications systems should be done, in my opinion. Without boring you more with the history, I suggest you visit Digital Mobile Radio Association where you will find a treasure trove of information and factual history about DMR. Contrary to many individual beliefs, DMR was not developed by Motorola and IS NOT proprietary to Motorola. Motorola did design their MotoTrbo line of radios based upon the DMR standards and they have continued to add features and functionality to their product line to fit their marketing plans. The only Motorola proprietary technology in use in the DMR network we use is a feature known as,  IP Site Connect (IPSC) which I will discuss later on. You ARE NOT restricted to Motorola radios on the DMR network, contrary to the belief of many. The DMR communication mode uses a technology known as Time-Division Multiple Access (TDMA) which is similar to cell phone technology, but it IS NOT encrypted. Simply put, the TDMA protocol allows two separate communications paths (voice, data, or other) at the exact same time on a single 12.5khz channel. In the DMR world, these two paths are referred to as, Time Slots (TS).

So, how does it work?

Let us assume that you want to install a repeater using the DMR standard and you want to coordinate it with SERA. You can find great information on how to do this by visiting DMR-MARC, The Motorola Amateur Radio Club, where you will find a lot of information including programming instructions. Once you feel like your head is hurting enough, you need to visit DMR USER / REPEATER Registration where YOU MUST register for a repeater ID as well as for your subscriber (portable and mobile). However, you cannot apply for a repeater ID until you coordinate a frequency pair for the repeater, but you can request a subscriber ID anytime. To coordinate your repeater pair, you only need to visit SERA, Southeastern Repeater Association , click on Coordination Tools, and then finally click on New Request to apply for a new frequency pair at your proposed location. Be patient as we are receiving an unusually high number of applications for DMR pairs. If you are uncertain about the coordination process, first visit www.sera.org. If you still have questions, please contact your State Vice-Director or Director who will be more than happy to assist you with the coordination process. For purposes of this article, pretend that you have now received coordination from SERA, your repeater is installed, and you have applied for and received your repeater ID. You install your repeater, power it up, and call CQ; nobody answers. In order for the repeater to function on the DMR network, it must have an internet connection at the repeater site and it must connect into one of the network c-bridge units from the various groups. You see, according to Motorola, you can connect up to a maximum of 15 repeaters in an IPSC network and obviously, there are more than 15 repeaters on the DMR Network. In South Carolina, we connect to NCPRN which you can find on the web at DMR USER / REPEATER Registration . The c-bridge acts as a traffic cop routing the repeater and the talk group. WAIT! What in the world is a talk group?!

Talk Groups

Talk groups are the toughest part of DMR for most people in both the commercial and the amateur world to understand. The best way I know to describe a talk group is that it is a virtual channel and some people refer to them as PL tones. If you remember the community repeaters which used multiple PL tones on a single repeater to accommodate multiple user groups, you will get the talk group concept fairly easy. Each talk group acts similarly to the different PL tones from the old community repeaters. Lets assume that you have your repeater connected to a c-bridge, you want to get on the PRN talk group, and your repeater is the only repeater you have programmed in your radio. Each channel position will have the same frequency programmed, but with a different talk group. There is one major piece of information you need to know for each channel; which Time Slot do you use? You can find that information on both the DMR-MARC websites as well as the NCPRN website. You must have the correct frequency, talk group, and Time Slot for each channel programmed in your radio or you will have a, failure to communicate. The folks at NCPRN have built example codeplugs (the files created by the respective radio programming software) that are free to download. If you are considering getting into DMR, please take the time to look at both the DMR-MARC and NCPRN websites and read through the instruction thoroughly because it will save you a lot of headaches.

Pros & Cons

So what are the pros and cons of DMR in amateur radio? The two biggest cons of DMR rest with the dependence on the internet and that you must use a commercial type radio. However, your local repeater will continue to work locally without an internet connection. As for commercial radios, Jerry Wranger, CEO of Connect Systems, offers a great DMR portable that is currently selling for $180 each with a free software download on his website Connect Systems . The radio you are looking for are the CS700 (UHF) and CS701 (VHF) and you can add an additional $5 per radio if you want a programming cable with it. This radio is also FCC Type Accepted for commercial use, but you MUST be an authorized or licensed user of commercial frequencies. This radio is also one of the pros in that you can get on DMR very inexpensively when compared to other traditional amateur radio communications gear. If you are a die-hard Motorola fan, I suggest you visit Ebay where I found a Motorola XPR6550 for $350 with a battery, charger, and antenna. *IMPORTANT* If you choose to buy a Motorola brand radio, make sure you get a radio with the 403-470mHz range as there are a lot of radios on the market that are 450-512mHz and are a little bit of a challenge to program into the ham band The pros to this technology are the efficient use of limited spectrum when compared to other FM modes. Additionally, DMR supports GPS location, text, private call (not encryption), and group alerts. Most networks do not support GPS on network Time Slots, but you can use this feature locally. In our testing, we have noticed an increase in communication range when using the DMR digital over analog when using the same equipment and repeaters. An additional pro is the cost of the actual repeater which will run you around $2,000 less duplexer, antenna, and hardline. One huge success that we have found is the use of deployable DMR repeaters. Here in Anderson County, we host a Communications Trailer equipped with a broadband satellite internet system and various other IP technologies. We installed a XPR8400 repeater in the trailer and connected that repeater to the NCPRN network. We were pleasantly surprised to find that there was no latency and no packet loss affording us yet another tool in our disaster readiness tool box. Yes, there are other mode and bands on the trailer as well, but it was very exciting to talk on a CS700 through the satellite connection to users in Virginia, North Carolina, and South Carolina as if we were talking on a mountain top repeater. This will be a great resource during ice storms and hurricanes along with other areas. As a side note, we are working on coordinating a commercial UHF repeater to provide public safety redundancy using the same satellite system back to our 911 Center. Another example of how amateur radio is leading the way!

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Last, but not least, let me suggest you take a look at the Amateur Radio Guide to Digital Mobile Radio (DMR) which can be found at Amateur Radio Guide to Digital Mobile Radio (DMR) – TRBO.org . I am excited to see new technologies especially when it is affordable to the amateur community. Remember; we are only amateur by title according to the FCC. As a rule, we should be professionals who enjoy an awesome hobby.

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73’s and keep the hobby going!

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KN4SWB, Matthew

W3KH has written 10 articles

December 18, 1946 - October 12, 2016, SK