Introduction to Amateur DMR
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An overview of Digital Mobile Radio (DMR) for amateur radio operators. Presented to the Laurel Amateur Radio Club (LARC) on 1/24/2018.
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Introduction to Amateur DMR
- 1. Introduction to Amateur DMR Andrew Beard AB3U January 24th, 2018
- 2. Basics • Usually associated with Motorola, but there are many DMR vendors • Used on VHF and UHF bands, but more amateur use on UHF • Primarily a commercial spec. Make sure your radio supports amateur frequencies! • Three types of DMR • Tier I: Simplex • Tier II: Repeater • Tier III: Trunking
- 4. DMR FM Narrowband 30 ms FM Wideband DStar (6.25 kHz) Time Frequency
- 5. DMR FM Narrowband 30 ms FM Wideband DStar (6.25 kHz) Time Frequency
- 7. DMR Audio Quality vs Analog FM Audio Quality Signal Strength Analog FM DMRGood Poor Strong Weak
- 8. DMR IDs • Every user has a unique 7-digit number that identifies them • Amateur DMR: Linked to a name and a callsign • Repeaters use a similar 6-digit convention with the same regional code • Every transmission is tagged with a user ID • List of IDs, callsigns, and locations is public 3 1 4 2 2 5 5 Regional Code Sequential User Number
- 9. www.dmr-marc.net • Regardless of the network, all amateur IDs are managed by DMR-MARC • DMR IDs are free, and you don’t need a radio to register • Fill out the form • You will need a callsign • Takes about 3 days to get a response via email • That ID MUST be programmed into your DMR radio
- 10. Repeater Linking • Analog FM repeater, frequency with offset and maybe PL tone • Linked analog repeaters are exceptions, not the rule • DMR linking is formalized, occurs via TCP/IP (over the Internet) • Step one, separate the conversation from the repeater • Core concept of DMR Tier II
- 11. Talk Groups • All client transmissions are coded with a single Talk Group (TG) • Repeaters send TGs they’re configured to repeat • In amateur use, usually organized by area or language • Supported talk group can be static (always connected) or dynamic (PTT) • Dynamic groups are linked temporarily when a client transmits a messages coded to that TG
- 12. Talk Group TG TS F/PTT Source World Wide Calling 1 1 PTT** DMR-MARC North America Calling 3 1 F DMR-MARC WW English Calling 13 1 PTT DMR-MARC WW German Calling 10 1 PTT DMR-MARC WW Spanish Calling 14 1 PTT DMR-MARC WW Nordic Calling 17 1 PTT DMR-MARC Local2 2 2 F Local Network Local9 9 2 F Local Repeater Midwest Regional 3169 2 F/PTT* DMR-MARC Northeast Regional 3172 2 F/PTT* DMR-MARC MidAtlantic Regional 3173 2 F/PTT* DMR-MARC Southeast Regional 3174 2 F/PTT* DMR-MARC Southern Plains Regional 3175 2 F/PTT* DMR-MARC Southwest Regional 3176 2 F/PTT* DMR-MARC Mountain Regional 3177 2 F/PTT* DMR-MARC TN State 3147 2 F/PTT* DMRX (VOLNET) VA State 3151 2 F/PTT*β K4USD MD State 3124 2 F/PTT*β K4USD DC State 3111 2 F/PTT*β K4USD
- 13. DMR Channels • One conversation via one repeater • Consist of: • A repeater frequency and offset • A time slot (1 or 2) • A talk group • A color code (like a PL tone)
- 14. Keying Up • Radio sends a packet to the local repeater with user ID, destination TG, CC • Repeater sends a message back to the user saying if they’re permitted or not (may result in a Talk Permit or Denied tone) • If the repeater isn’t current linked to that TG, it will contact the responsible bridge or peer • Transmission is distributed to other repeaters who are listening to the same TG
- 15. DMR Networks • DMR-MARC • Uses Motorola IP Site Connect (IPSC) for linking • Contains K4USD network (including K3UCB in Ashton) • No hotspot support • DMR-plus • BrandMeister
- 17. Hotspots • Low-powered transceiver that connects to a DMR talk group via the Internet • Many support DMR, DStar, C4FM • No local repeater needed SharkRF openSpot Wireless Holdings dv4mini PE1PLM DVMega w/ RPi
- 18. Things To Remember • Airtime is a resource • You can’t (usually) just listen to dynamic talk groups • TDMA is sensitive • Beware ”Tier I” or “Slot 1” radios
- 19. Tytera (TYT) MD-380 • Single-band 5W HT • Available from Amazon for less than $100 • Most common DMR radio in amateur use • Modified firmware available (see md380tools) • MD-390 also available (waterproofing, GPS) • Rebranded by others (Retevis RT3)
- 20. Other Vendors • Motorola (MotoTRBO series) • Connect Systems • Hytera (PD series) • Kenwood • Vertex Standard • Baofeng
- 21. Things That Aren’t DMR • DStar • C4FM (System Fusion) + WIRES-X • P.25 (Project 25) • NXDN • dPMR
- 22. Why DMR? • Spectral efficiency • Power efficiency • Intelligible audio with poor connections • Repeater and Hotspot linking • Visibility with Last Heard • Lower cost than many other digital modes • Wide compatibility
- 24. Resources • Amateur Radio Guide to Digital Mobile Radio by W2XAB • K4USD Network • VA3XPR Code of Conduct
Editor's Notes
- Not going to do a step-by-step of how to get on the air with DMR Hopefully give enough of an introduction to get you interested in DMR, and an idea of what the next couple steps are
- Open standard defined by European Telecommunication Standards Institute (ETSI) Technically supports anything in 66 to 960 MHz Trying not to use the word channel here, since that has a different connotation for DMR (more on this later) Tiers are a simplification
- TDMA, Codec, then protocol
- Spectral efficiency TDMA – Power efficiency Time Division Multiplex Access DMR – 12.5 kHz bandwidth
- Usually tuned in to only one time slot at a time. Power efficiency, duty cycle 50%
- Amber codec Not part of spec, but used by everybody Vs AMBE Hardware only Error correction
- Originally taken from Vertex Standard slides, but adjusted Not to any type of scale, FM starts out higher quality than DMR, but a large portion of the time DMR outperforms because it’s so consistent Breaks up to the point of no signal faster, Compromise for commercial use
- Why an ID? DMR wasn’t designed for amateur use. In commercial applications there is no callsign. This is my DMR ID. 3124 is United States, Maryland. Everyone who registers a DMR ID in the state of MD will have an ID that starts with the same 4 digits. I am the 255th person to register a DMR ID in the state of MD. The guy after me will be 256, etc. Can do interesting things with that list.
- If you’re interested in using DMR, sign up ASAP. That last line is REALLY important. At this point, all DMR radios I’m aware of must be programmed with a cable. If someone borrows your radio, they are you until it’s reprogrammed. CAVEAT: md380tools firmware
- Linked analog repeaters implemented on a case-by-case basis KV3B vs WA4TFZ Repeaters do not have to be Internet linked, but most amateur ones are Voice data is already encoded, packetized, and tagged with source/destination. Specific protocols for linking are NOT standardized
- PTT talk groups – Length of time based on repeater configuration. Usually about 10 minutes.
- Just a sampling Will talk about that F/PTT column a bit later
- Color Codes – Must match what the repeater is set to accept. Integer value between 0 and 15. Usually (99% of the time for amateur use) it’s CC 1. Yes, Color Codes aren’t colors (thanks ETSI). Mandatory, unlike tones
- Reasons not permitted: Blacklisted user Unsupported talk group Color code mismatch Bad connection Another user transmitting The radio may emit a talk permitted or denied tone There may be a delay for linking
- Many networks, but three largest for amateur use Dictated by repeater hardware, NOT user radio. Users can join any network. DMR-MARC, Motorola only. Some talk groups area linked across networks. A lot of development, but a lot of it encumbered by patents and NDAs.
- Tell where people are active, who they are. A bit like a DX cluster or spotting network.
- In the 10-20 mW range Do not work for DMR-MARC network, but fine for DMR+ or BrandMeister They don’t decode the audio, no codec chip
- Talk about the always-linked TG problem. From previous list, North America Calling is linked full time to TS1. When I transmit, I transmit on one Talk Group. When I’m listening I get all the TGs on that time slot. The radio decides what I hear. Dynamic talk groups need to be linked. Unless someone has in the past 10 minutes, you can’t hear it. You need to key up Most linear amplifiers don’t work with TDMA
- Reason I mention most common, there is a LOT of community documentation. Codeplugs, etc. Includes charging cradle. USB programming cable, etc MD390, very similar. MD2017 (dual-band) md380tools: Add entire database of DMR users, show on demand Hear from any Talk Group without programming it in Change DMR ID from radio Show mic gain while transmitting
- Kenwood does not sell DMR in US Vertex Standard owned by Yaesu
- Dstar, started as a Japanese open standard. Almost entirely driven by ICOM P.25 – Designed for public safety, used for commercial as well NXDN – FDMA, same voice codec. Used a lot by rail industry dPMR - FDMA. European standard. Niche deployments, mostly small ones.
- DMR adoption increasing for a while, recently entering low-cost commoditization phase