Starting out you may look at all the information available and immediately become confused with all the terms used. I was like this when I first started and so here I have put together A Guide to DMR. This is put together from all the things I have learn while getting started with this mode.
We Will be going through the following sections on this page.
Introduction to DMR
DMR was originally invented between 2005 & 2009 when the DMR association was formed to control the usage of the mode in the commercial environment.
It was initially only a commercial protocol before being adopted by the amateur community.
It uses 4FSK (Frequency Shift Keying) and TDMA (Time Division Multiple Access)
Encoded using the AMBE+2 Codec
DMR networks exist that link repeaters via the internet.
The one thing that is often misunderstood is the face that DMR can be used simplex just like any other digital mode and never use any of the internet features.
Benefits of DMR
The benefits of DMR are that with the mode being originally commercial it makes the radios that are available cheaper then some of the other digital modes.
Data is also included in your voice transmission which includes your unique ID, Who the transmission is intended for again an ID, and sometimes other data like GPS location.
Transmissions can be directed to either a group or individuals.
TDMA allows 2 QSO’s to happen at the same time.
Basic Terms Used
- TX/RX frequencies
- These are exactly the same as when using FM. There are set simplex frequencies on the band plan and they follow the same conventions in terms of repeater input and output.
- They are more common on 70cm that 2m but there are some 2m DMR repeaters.
- Colour Code
- Colour codes are the DMR version of CTCSS. It is not a colour as such as it is just a number from 1-15 that you set in the programing.
- Radio ID
- A radio ID is a unique 6 digit ID number that is linked to your callsign. You need to apply for an ID before you use DMR. Issuing of ID’s in done in one of 2 places. Either through DMR_MARC, or if your from the UK through, ham-digital.org.
- Time Slot
- A time slot is the result of using TDMA mentioned above. Repeaters operate using 2 time slots conveniently names Time slot 1 & 2.
- Repeaters Quickly switch between Time slot 1 & 2. Your radio then listens to the time slot programmed.
- Group Call
- This is a transmission intended for a specific Talkgroup (See Talkgroups below)
- Private Call
- This is a transmission intended for a specific person / DMR ID.
- DMR Network
- There are a number of DMR Networks in the UK. DMR networks are a group of linked repeaters that can communicate with each other.
- You do not need to register individually for an ID on each DMR network as they all share the same User / DMR ID database.
- Each Network will have there own structure of Talkgroups and Repeaters and each one is slightly different
- The major Networks are:
- BrandMeister: Mostly in the midlands with some in the south. Some talkgroups linked to other networks and modes.
- Phoenix: The major network in the south east. Some talkgroups also linked to other networks and modes.
- UK DMR South West Cluster: As its title, Located in the South West with no links to other networks.
- Northern DMR Cluster: Mostly in the North West. Virtually Identical and Bridged to the Phoenix network but with a different group running it.
Talk Groups are basically rooms which are identified using an Code / ID. Each talk group on a network is usually assigned a purpose. For example Talk Group 2350 is the BrandMeister UK Calling Talk Group. You access a talk group my making a ‘Group Call’ to the talk group number. (Explained further in the Codeplug section)
Talk Group 9 is not sent over the internet and so should be used for using a repeater, as you would with an FM one, for local contacts. There is an exception to this explained later.
Repeaters can be set up using what are called Dynamic and Static Talk groups.
- Static Talk Groups
- Static talk groups are talk groups that are permanently assigned / linked to a Time Slot on a repeater. This means that any activity on the talk group is transmitted out on that Time Slot.
- This means that if you tuned your radio to the repeater and was listening on a talk group that is set as static then you would be able to hear it on your radio.
- Dynamic Talk Groups
- Dynamic Talk Groups are ones that are activated by you, the user.
- For example, if you tuned your radio to a repeater and was listening on a talk group that is not ‘Static’ then you would not her anything.
- To Access / use the talk group you need to link the talk group to the time slot by transmitting into the repeater to the talk group you want to link.
- You can then use the talk group as just like the static ones but if you do not transmit into the repeater on that talk group for a certain period of time then the repeater will disconnect from that talk group.
- By the user having to link the talk group and it being automatically un-linked after a period of inactivity is what makes them Dynamic.
- NOTE: Some repeater keeper request that linking of dynamic talk groups is only done on a specific Time Slot leaving the other slot available for the Static Talk groups. Please check on the website of the repeater you are using for specific instructions if there is any.
UK Brandmeister Talk groups are available here. This is my local network and the one I have most experience on,
Reflectors are similar to talk groups but are more like a conference bridge.
They can be set on a repeater in a similar way to Static and Dynamic talk groups. The only difference being is that all activity on a reflector is accessed using Talk Group 9. This is the exception talked about earlier.
If a reflector is staticly assigned to a repeater then all you would need to do is tune your radio to the repeater using Talk Group 9.
To access a different Reflector you need to make a private call to the Reflector number. This will link that Reflector to Talk Group 9 on the repeater and is usually on Time Slot 2. The reflector will be automatically disconnected after a period of time of you can do it manually by making a private call to ID 4000. If you are disconnecting a reflector in order to connect to a different one then do check it is not in use before disconnecting.
Private calls can be done using programmed memories although modern radios may allow you to type in the number and press the PTT.
Future of Reflectors
Reflectors are becoming less popular now due to the fact that more radios are being released that allow programming through the keypad. Back when DMR first started programming was usually only possible by connecting the radio to a computer. So a radio would be pre-proammed for a set frequency and Talk Group and the user could only type in a User ID to talk to a specific person if required. Amateurs took advantage of this an instead of typing in a specific users ID we would type in the reflector ID which instructed the repeater to connect.
Now most radios allow the programming of new frequencies and specifically new talk groups into the radio using the keypad reducing the need for reflectors.
This is why BrandMeister are removing Reflectors from their network and using talk groups only.
Understanding the DMR Tiers is not strictly necessary but knowing which Tier your radio is, is very important.
- TIER 1
- Simplex only. No Time slots. This means it cannot be used on amateur repeaters as it would use up both time slots.
- The original Boefeng DM5R was Tier 1 only. DM5R+ had Tier 2.
- TIER 2
- Supports 2 Time Slots (TDMA). What us Amateurs Use
- TIER 3
- Advanced Trunked system. Complicated Commercial system allows for automatic repeater switching plus many other things.
- Similar to the Airwave system used by the emergency services.
Most people when they first encounter a code plug or get told about them believe they are confusing and complicated. To the uneducated eye this may be what it looks like. But following a simple set of rules should make them easy to understand, create and modify.
Codeplugs are usually created within the manufacturers CPS (Customer Programming Software). There are other 3rd party programs available with most software having the ability to import and export .csv files. This allows for easier editing within a program such as excel.
Codeplugs consist of the following elements:
These are a list of ID’s for talk groups, reflectors and individual users. Each contact can be set as either a group or or private. This set weather it would be a group call or a private call as mentioned in the Talk groups and Reflectors section.
These are what you would more associate with programming an FM radio. Channels contain the RX and TX frequencies, the colour code and the contact that you wish to communicate with.
You would need to create a separate contact for each talk group you wished to use on a repeater. So all the contacts would be the same except for the Contact. This leads nicely onto Zones.
These are basically a group of contacts. These are created entirely at the users discretion. You could group contacts for a particular repeater or region for example.
These elements come together to form the programming file or Codeplug for a radio.
Below is a screenshot of a channel in the CPS for a TYT MD-UV380. The highlighted items are the essential ones to have set correctly.
This is a screenshot of my zone for GB7LN which includes the channel above.
Hotspots are small internet connected transceivers which are usually only 10mw in power. They are simplex devices so cannot transmit and receive at the same time.
There are two main types of hotspot. Pre-Built units like the ShackRF and module types like the MMDVM which need pairing with a Raspberry Pi.
The ShackRF is a commercial product that, apart from filling in your callsign etc.., is ready to use out the box.
MMDVM is open source hardware which you assemble with a micro computer like a raspberry pi. This is more of a build it yourself type as you need knowledge of writing SD cards and sometimes soldering of the headers.
The software used MMDVM is called PiStar which is a group of programs preinstalled on a Raspbian image ready for you to copy onto an SD card and setup from there.
I will soon be Experimenting with MMDVM and PiStar so I will do a separate guide on installing and setting this up.
DMR Do’s and Don’ts
As mentioned, some talk groups are allocated as calling talk groups. When calling on these groups don’t call CQ but announce yourself with your call sign and the talk group you are calling into and say that you are looking for a contact.
Once you have made contact with someone you should move to a ‘Chat’ talk group. For example the UK calling talk group on BrandMeister is 235. The UK chat talk groups are 2351, 2352 & 2353. 2350 is also a UK chat talk group but is linked to the Phoenix network so should be left clear if you don’t require the link.
Finally as with all repeaters, you should leave gaps between your overs. Firstly to allow others to break in but also because of the internet links in use and more software powered repeaters it allows time for latency and for the repeaters to switch between RX and TX correctly.