Intro to DMR

The Rocky Mountain Ham Radio DMR Network – An Introduction
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DMR (Digital Mobile Radio)
Digital Mobile Radio (DMR), sometimes referred to as MotoTRBO or just “turbo” the Motorola branding in the USA, is a repeater technology that uses a narrow band digital FM, 12.5 kHz channel bandwidth, as opposed to the 25 KHz bandwidth of conventional analog FM. There are three “tiers” of DMR, Tier II and Tier III are based upon Time Division Multiple Access (TDMA) technology where a single repeater frequency pair has two (2) communication channels called Time Slots. Time Slots allow for two simultaneous conversations on one repeater frequency pair to take place. This is the type of DMR system that is utilized by the Rocky Mountain Ham Radio Network. None of this requires anything more from the user other than programming your radio to the appropriate time slot and talk group for each repeater site. Our repeaters are listed in DMR Site Information.

Talk Groups
The Rocky Mountain Ham Radio Network has multiple Talk Groups, these are abbreviated “TG” in the RMHAM sample code plugs. These Talk Groups allow the seamless linking of RMHAM’s repeaters that are on the Rocky Mountain Wide Talk Group 700 TG700 that serves the entire system.  There are also Regional Talk Groups serving smaller geographic regions that are linked using their individual talk groups and some talk groups that are specific to localized areas that are only used on a single repeater. There are three (3) main regional talk groups Northern Colorado Regional Network (No CO) – Talk Group 721, Central Colorado Regional Network Talk Group 720, and Southern Colorado Regional Network (So CO) – Talk Group 719. Other talk groups on the Rocky Mountain Ham Radio Network include the Eastern Talk group Talk Group 705 which is VHF and has some unique experimental features! Our brethren to the south have the New Mexico Regional Talkgroup (NM) Talk Group 505 Four Corners Regional Network (4Corners) Talk Group 745. A listing of the other localized Talk Groups is HERE.
PLEASE READ all of the notes associated with each Talk Group! This is very IMPORTANT! As the Rocky Mountain Ham Radio Network continues to expand, certain regional and local features may exist that you need to be aware of!
The Rocky Mountain Ham Radio Network is a dedicated network that is not part of any other DMR system. It is always up and ready to use, provided you have the proper programming for the network’s repeaters in your radio. Please remember that any time you are on Rocky Mountain Wide or any of the Regional Channels, when you bring up that channel you bring up ALL the repeaters in that Talk Group. If you get the Talk Permit Tone on DMR, it sounds like “tweedle”, you are connected to the repeater and it is free for you to transmit. No “Kerchunking ” Please!

Zones
Zones make it easier to organize and use your radio in various geographic areas on the network. The network is divided into four (4) Zones and are programmed as such in the RMHAM sample code plugs. DMR North (TG721), DMR South (TG719), and the Central Zones DMR CentralEast and DMR CentralWest (TG720). Central is divided into East and West due to the limitations of many radios that only have 16 channels per zone. The sample code plugs also contain many analog repeaters in various zones, but this article will deal with the Rocky Mountain Ham Radio DMR Network. A typical DMR Zone will contain the RMHAM repeaters within the zone’s geographic talk group. It is programmed with both time slots for each repeater at each site and the applicable talk group for each time slot. As you travel throughout the region, select the Zone corresponding to your location then select a repeater with either the Rocky Mountain Wide or the Regional talk group for the region that you are traveling in and you’re all set.

Sample Code Plugs
These codeplugs are designed to get amateurs who wish to use the Rocky Mountain Ham Radio Network up and running quickly. They are specific to the Rocky Mountain Ham Radio Network and the geographic areas that it covers. The talk groups are typically labeled with the Repeater Location and the talk group’s name abbreviated such as “Rk Mtn” for TG700 Rocky Mountain Wide.. As an example, the repeater located in Akron, Colorado has a channel name of “Akron Rk Mtn”, located in time slot 1 at the Akron site. The Rocky Mountain Ham Radio sample code plugs have been created for a wide variety of popular DMR radios. Always remember to place your unique DMR identifier in the radio’s ID field when starting to use a RMHAM sample code plug! These code plugs contain all the correct programming for all the repeaters in the Rocky Mountain Ham Radio Network. You are encouraged to create your own customized code plug, unique to your radio and your needs, by adding any DMR systems and/or analog repeaters that you need. The RMHAM sample code plugs are HERE.

The Roam Feature
Many DMR radios that are Tier II and Tier III compatible support roaming. A properly programmed roam list will allow your radio to automatically select the best repeater for you to use. This will be the repeater with the highest Received Signal Strength Indicator (RSSI). If the RSSI drops below the level set within the receiver, the radio runs through the list of channels looking for a repeater that meets or exceeds the RSSI level. All Rocky Mountain Ham Radio Network repeaters send out a ping every 60 seconds, which the radio can listen for to determine if that site has met the RSSI level requirement. This makes using the system extremely easy. Your radio automatically picks the repeater with the best signal without you having to do anything.

Radio Etiquette

It’s not good radio etiquette to do “Radio Checks.”  If you wish to test a new antenna, a new codeplug or a new radio, simply get on the radio and have a conversation with someone about your new configuration.  Amateur radio operators communicate with each other, so just have a chat.  You might just learn something!  Rocky Mountain Ham Radio strongly discourages radio checks on our networks.

Enjoy!
Please feel free to make yourself at home on the Rocky Mountain Ham Radio Network and enjoy using it. Remember to check out the rest of rmham.org for all of the other services that we offer!