DMR For EmComm

What is EmComm?

EmComm, or Emergency Communications is the practice of providing communication services during emergency response, especially in situations where traditional communication modes may not be available.

The primary role of ARES is to support the emergency management community (responders, relief and recovery agencies) with communications during times of emergency and disaster when normal communications are unavailable or overwhelmed.

We are communicators not first responders. If you arrive at the scene of an emergency just as the sirens are quieting, check in, keep your mouth shut ,and get out of the way until you get an assignment. We do not provide first aid, transport victims, provide traffic control or any other function normally provided by public service agencies, nor are we running the show. We DO provide communication when public service communications systems are overloaded. We do not “self deploy.” We deploy when a partner agency requests our services.

Many hams think of ARES as a simple extension of the “talk time” in the hobby. This is not true. ARES are organizations that continually learn, train, and develop the skills needed to be part of the emergency response machine. We always need more trained operators that are willing to learn to communicate rather than just talk. Do you have the time and the drive to do it well?

The goal is to provide trained operators that have learned to communicate accurately, clearly, and concisely in a timely fashion regardless of the obstacles in the event. One tool for communication is DMR or Digital Mobile Radio.

What is DMR?

DMR is a radio protocol that uses digitally encoded signals instead of traditional analog signals. This is much like the difference between playing an old LP record that directly recorded analog sound versus playing a CD where the audio is encoded as bits and bytes – these bits and bytes are what is transmitted via the radio signal.

Why use it?

There are a number of reasons that make DMR a good choice for EmComm:

  1. Unlike analog radio – there is no ‘fade’ as a signal gets weaker. As long as the signal gets through the audio is clear and readable. This cuts down on the need to re-transmit messages when there are high levels of noise.
  2. DMR is much more efficient in terms of bandwidth. Using much narrower slices of the radio spectrum, and time slicing the available frequencies (more on this later) as many as four conversations can be held using the same bandwidth that one analog communication would take.
  3. DMR can be more capable – since the exchanges are digital text and data can be exchanged alongside the voice exchange. This can include position information, short text messages, and more.

But there are also a few downsides – most significant is the fact that a DMR exchange either works or it fails – completely. With analog radio, a trained operator can pull voice traffic out of very noisy backgrounds. This can be important in an emergency. With DMR, you generally either have a clear voice with little or no background, or you have nothing – literally nothing. So lets talk about how DMR does its thing.

DMR – How it works

DMR does its magic by squeezing your conversation into a really small space. It does this by converting the audio to digital data. Then, since the binary data does not require as much bandwidth as a voice, DMR only needs 6.5kHz instead of the 12.5kHz that voice takes. Finally, it is possible to use two separate time slices (TS1 and TS2) to share one frequency between two separate transmissions. So in the same bandwidth as one analog transmission, you can squeeze 4 (A, B, C, D) digital transmissions.

One Continuous Xmission

TS1

TS2

TS1

TS2

TS1

TS2

TS1

TS2

1 Analog Transmission (12.5 kHz)

A

B

A

B

A

B

A

B

6.5 kHz

C

D

C

D

C

D

C

D

6.5 kHz

Now to make this work, the radio needs to know some specific things to set up a transmission.

Time Slots

First, it needs to know which of the two time slots your conversation will use – both radios, yours and either another DMR (simplex) or the repeater need to agree. Because if you are on TS1 and they are on TS2, you won’t be able to communicate.

Color Codes

Color Codes are a lot like PL tones, they allow your radio to filter out transmissions you don’t want to hear. But, both ends have to agree on the same color code, or your buddy’s radio will filter out your call.

Talk Groups

Now, when you have all this digital data flying around, its kind of like email – you need to know the email address of the recipient. That’s where talk groups come in. Having set up the correct time slot, and agreed on the same color code gets the radios set up to be in sync. But, they also need to know how to address the data. So, you also agree on a talk group. Then everybody who is on the same talk group can hear and talk to each other.

Okay, with simplex operations, this isn’t that important. And if you are both on the same repeater, you could work around it. But once the data is digital, it opens a world of possibilities in terms of linking repeaters – even ones that are hundreds of miles apart. And to do that, everybody needs to agree on the same talk group.

For emergency communications this is a very powerful tool. Our group, Denver ARES, is part of a public safety team for the major interstate I-70. The East region stretches from Denver to the Kansas line – over 170 miles of road. Thanks to the wonderful people at Rocky Mountain Ham – we can use one talk group (Central) and have a conversation with ARES members at the other end of the state – and do it with HTs at each end.

“Okay, okay,” you might be thinking, “You’ve sold me – how do I get started with DMR?”

What do you need (and where to get it)?

It is pretty easy, actually. You only need 3 things:

  • A DMR ID that is programmed into your radio as your personal ‘address’
  • A DMR radio, and
  • A CodePlug – the configuration file that the radio uses to know what to do.

DMR ID

A Radio ID is a unique number assigned to you (and your callsign) by the RadioID.net team. It is kind of like a telephone number or IP address. Your Radio ID identifies you as a unique radio user on the various DMR networks and repeaters around the world. You need to have a radio ID to use a DMR radio.

To get your Radio ID, you need to register with RadioID.net and upload an official copy of your Amateur Radio Licence. For U.S. radio operators, that can be done by1:

  1. Log into FCC system at https://wireless2.fcc.gov/UlsE.
    1. The FRN and password are the same you use when applying for Vanity callsigns and address changes.
    2. If you don’t know your FRN number, go to FCC ULS License Search and search for your callsign. Your FRN will be listed in the column FRN.
  2. On the left side menu, click on ‘Download Electronic Authorizations’.
  3. On the new page, select your callsign and click on the button ‘ADD >’.
  4. On the bottom right of the page, click on the button ‘Download >’.
    1. Make sure your pop-up blocker is disable, otherwise you won’t be able to download the PDF for your license.
      5. You will be asked to save a PDF file. Save it and submit it to RadioID, Simply create your account at RadioID and upload the License.
  5. That’s it. You will receive an email, usually within 24 – 48 hours, with your unique Radio ID, which you can promptly program into your radio(s).
    1. Note: You only need one radio ID even if you have multiple radios.
    1. DMR Radio

      Okay, yeah – you are going to need a DMR radio. There are too many on the market for us to give you a good overview.

      But, keep in mind that in many cases Emergency Communications groups, like ARES, will maintain a cache of radios to be distributed in the case of a deployment. So check with your team to see what is available.

      CodePlug

      In many ways setting up a DMR radio is just like setting up an analog radio that is used to connect to repeaters. While Code Plug sounds like some odd programming process, it is really just a configuration file. It will generally have three sections:

      • A Contact list – which are the talk groups you want to use
      • Channel Information – this is just like setting up a repeater, frequencies, and offsets, but you need a few more things for a the DMR like the time slot and the color code and so forth
      • Zone information – this lets you organize the talk groups and channels into groups that can be arranged by purpose (EmComm, Personal, etc.) or geography (North, Mountains, Vacation house, etc.)

      While you can build a code plug starting with a blank sheet, more often you will start with an existing Code Plug, and modify it to fit your needs.

      For EmComm usage, it is important to have a common operating model. Since many EmComm groups have caches of DMR radios to be distributed during a deployment, they will be programmed with a standard code plug that meets the needs of the group and its partner agencies.

      So, get the code plug approved by your group, or that is distributed for a specific emergency response.

      Operating procedures

      With an analog radio pressing the PTT immediately keys the transmitter and you’re ready to go. Not so on a DMR radio. When the PTT is pressed, a signal is sent to the repeater which checks to see if the Time Slot is available. If it is, a data stream is sent back to the radio giving you the All Clear, usually generating a beep tone. This occurs in just under a second.
      It is highly recommend that the BCLO (Busy Channel Lock Out) function is enabled. This prevents a station from transmitting on a Time Slot if it is currently active. Another indicator that the TG is in use is an activity light on the handheld. If the LED is lit, the Time Slot is in use.

      Busy Repeater Channel / Time Slot

      You may see the Channel Busy indicator lit, but not hearing a conversation. This is caused by someone activating or using a repeater Talkgroup other than the one you are monitoring.

      Digital Monitor

      Your DMR radio may have a ‘programmable key’ function labeled Digi Monitor or Promiscuous mode. This open allows you to monitor all activity on one or both time slots regardless of the Talk Group in use. This is a monitoring function only.

      General Rules:

      • 3 second pause before PTT
        • This allows for network latency as well as a courtesy pause for those wanting to enter the conversation.
      • 1 second pause after PTT
        • This is required for your radio to sync with the repeater and network.
        • You will get the Go Ahead signal if the repeater is clear.
      • Time Slot in use
        • This is usually shown by an indicator light or a time slot busy tone on your radio.
      • Talkgroup in use
        • You may not immediately hear an active Talkgroup. When switching to a different TG, your radio may need to sync to a conversation already in progress.
      • Announcing your presence
        • Announce both your Call Sign and Talkgroup. This will allow someone who is scanning to identify your Talkgroup so they can answer your call

1These instruction are adapted from the ones provided by DMR For Dummies: https://www.dmrfordummies.com/dmr-radio-id/