Having read the comparison between the various modes of Digital Radio, DMR will undoubtedly stand out as the best value for money considering the price of basic Chinese manufactured equipment such as Anytone, Tytera, Retevis and Aluence. In Ireland, DMR seems to have become the more popular of the modes available at present. A Tytera dual band DMR Radio can be picked up for very reasonable money on Ebay. In the Galway Area a UHF single band Handheld will suffice with the coverage of the Local Repeater EI7RHD and proposed expansion of the network with three additional Repeaters.
The DMR radio is not operable straight out of the box and needs programming which does tend to be a stumbling block to some operators. This program is referred to as a Code Plug. In many cases. somebody will have written a comprehensive Code Plug for their area which may be of use. A Code Plug written for the South Eastern area of Ireland will not suit the West of Ireland as the Repeaters or Gateways will be on different frequencies. If one is using a personal Hotspot it will be possible to program many channels for use on a simplex digital frequency from which the Hotspot will operate. As the infrastructure expands around Ireland it will be possible to program an All Ireland code plug.
Initial programming does not have to be complex. Start by programming just the three Irish channels. If no difficulties are encountered it is possible to expand the Code Plug to encompass UK and follow on by adding International channels.
Terminology
A few basic terms need to be understood before proceeding to th programming of the Radio.
Time Slot
DMR uses Two-slot Time Division Multiple Access (TDMA) allowing two channels in 12.5 kHz of bandwidth using the AMBE+2 proprietary codec (or vocoder, voice encoder). “Spectrum efficiency of 6.25 kHz” is often used although ‘it really uses 12.5 kHz, half the time.’ An illustration of the difference between an Analog signal and a DMR TDMA signal is shown below.
As there are two time slots it is possible to hold two conversations at the same time - One on Time Slot 1 and the other on Time Slot 2. Effectively this is the equivalent of having two repeaters on the one site but only using one TX/RX, one set of cavity filters and one antenna.
A user can only access one time slot at a time. Two Talk Groups cannot be accessed on the same Time Slot simultaneously. Each Time Slot occupies the signal for less than 30ms at a time. Within a
60ms window on a repeater: Time Slot 1 is transmitted for 27.5ms, then a
gap of 2.5ms, Time Slot 2 is transmitted for 27.5ms, another 2.5ms gap,
and then repeats with Time Slot 1. As there is slight latency in the demodulation of the DMR signal, the human ear will not detect that
small of a gap in audio. A repeater transmits both time slots even
though one channel is in use and the other idle. This cuts down on the
on/off keying of the repeater. User radios, on the other hand, transmit
for 27.5ms each 60ms window. This results in extended life of the
handheld battery.
Talk Groups (TGs) - A way for groups of users to be separated on each time slot, without
distracting or disrupting other users, is to use Talk Groups. The radio
stays muted until the assigned Talk Group appears on the frequency,
then it will unmute or activate for that transmission.
.
Ham radio Talk Groups can be created for any purpose and usually fall
into the categories of Wide area (worldwide), Regional or for a particular purpose or group. In Ireland TG 2722 is a Calling Channel, TG 2723 is a Chat Channel and TG 2724 is a bridge between DMR and Yaesu Fusion. TG 2724 is connected into YSF Ireland allowing those on Yaesu Fusion to communicate with DMR users. The UK has a number of Talk Groups, UK Call, three Chat TGs and a number of Regional TGs.
TG 91 is a worldwide Talk Group monitored all over the world. Europe has a specific English speaking TG amongst others, the United States has a Nationwide call TG and also many regional TGs for each call sign area.
In Ireland we tend to allocate Time Slot 1 to International Talk Groups and Time Slot 2 to our Domestic TGs and UK. Bear in mind, that calling on International TGs may come out on many Repeaters at once so do request that a longer QSO is conducted on Time Slot 2 on a "chat" TG.
TG 9 is a talk group assigned for non specific use. If calling another station point to point, the use of TG 9 will be a common meeting point. If used via a repeater, the Repeater will behave like a normal voice repeater and just relay the up-link. Any other Talk Group will be routed through the network to its destination. An example, TG 2722 would route through the whole network for a general call.
Static TGs - A static Talk Group is a talk group programmed onto the Repeater on a specific time slot. If a call should be made on this TG, then it will be automatically relayed through the repeater. Sveral Static Talk Groups may be programmed onto a repeater. International TGs would be programmed to TG 1 and Domestic and UK TGs on Slot 2.
Dynamic or User Access (UA) TGs - Dynamic TGs are those selected by the user. These are pre-programmed into the Radio. On pressing the PTT they will automatically routed through the network. If one selects another Dynamic TG, the Repeater will disconnect from the one previously used and connect to the newly selected TG. If a Dynamic TG has not seen any use for 15 minutes, it will automatically disconnect from the network.
Reflectors - are similar to D-Star or IRLP reflectors, where nodes are connected in a round table type configuration. When one station transmits, their signal is transmitted by all other
connected nodes. So far, these sound like Talk Groups. The difference is
reflectors are available worldwide and repeater users have to
specifically link and unlink a reflector. This means only repeaters and
hotspots connected to that reflector are tied up during transmissions
and not thousands of repeaters on world-wide Talk Groups.
A Reflector has a 4-digit ID that begins with a 4, as in 4xxx. Reflectors are only available on Time Slot 2 via the Brandmeister system. To disconnect from a Reflector on keys in 4000. Reflectors may be programmed into a memory bank. Brandmeister have this ability. Some reflectors are cross-patched to
Talk Groups on Brandmeister so either the reflector or Talk Group ID can
be used. Reflectors are seldom used on Brandmeister because of the
availability of all Talk Groups to all repeaters and hotspots on the
network. However, reflectors still serve the intended purpose if a
station isn’t in range of a Brandmeister repeater.
Contacts - There are three call types in DMR: Group Call, Private Call, and
All-Call. Each is a contact within the radio. A Group Call is a
transmission from one radio to a group of radios. These instantly
link-up dynamic Talk Groups when PTT is pressed.
An example of a Group Call would be TG 2722 (Ireland Calling Channel) When the PTT is pressed, any radio linked into and listening on TG 2722 will unmute and the call will be heard.
A Private Call may be initiated from one radio to another using the Radio user's ID point to point or via the network. If the radio called has used the network the call will be routed to the last known Gateway or Repeater - a little like D-Star! Private Calls are discouraged on the network as they can tie up a Time Slot or even break into an existing QSO on the destination Repeater. A Private call may only be returned if the originator's ID is programmed into the destination radio.
All Call is a facility used by a supervisor on commercial systems and will result in the call being heard by ALL users on the given time slot. This is NOT used under any circumstances on an Amateur Network for obvious reasons.
Getting Started
It is necessary to register for a DM ID number which is your personal ID and this will link to your call sign and name. Registration for a DMR ID may be obtained >>
Here.
Follow the instructions and have a PDF copy of the front page of the license to upload completing the registration process. The ID is issued within 24 hours. Follow the steps below and programming will become second nature. Rome wasn't built in a day, and neither will your code plug!
The order in which programming is done is as follows:
1) Contacts
2) Channels
3) Zones
4) Placement of Channels in Zones
The programming software for an individual radio is down-loadable from the manufacturer's website, or on a disc supplied with the radio. In this brief tutorial, it is the Tytera MD-380 or clones such as Retevis or Zastone handhelds programming described.
On running the program this is the first screen that will appear
If the set is a UHF handheld, this is the basic information see. Attach the programming lead supplied with the radio to the computer and then switch the radio on. Look along the toolbar of the program ans to the right of the disc symbol there is a picture of a handheld radio with an white arrow pointing to the left. Click on this and anything programmed into the radio will be downloaded to the program on screen. Normally, there is one channel as an example already in place. The view shown is the Basic Information which is the first item in the menu.
General Settings
Click on General Settings and the following screen will appear
Look at the positions highlighted by the red arrows. The Radio Name is your Call sign and this is typed in Capital Letters. The Radio ID menus the DMR registration number assigned to your call sign. The two boxes shown at the bottom right of the screen can contain in Line 1 - your name and Line 2 - your call sign. These may be left blank as they will not affect the operation of the radio. Best to leave all of the other settings alone until a greater understanding of the radio is realized.
Contacts
On the menu, click on Digital Contacts and this screen will pop up
Click "add" at the bottom of the screen. Enter the name of the contact in the "Contact Name" box - it is possible to replace the words "Contact 1" with the name required/ Click on Call type and three options will be available on the drop down menu. Most Talk Groups will be
Group calls, whilst individual call signs will be Private Calls. Enter a contact here which may be a Talk Group, Reflector or an Individual.
Any number of contacts can be added to this box for future use
To program a channel the layout would be as follows:
No Contact Name Call Type Call ID
1 Ireland Call Group 2722
2 Ireland Chat Group 2723
3 YSF Ireland Group 2724
4 EI4ALE Private 12345
A complete list of individual Talk Groups may be found >>
Here
Ireland Call is the Irish calling channel. It is a Talk Group and will be a Group Call so all can hear that call when it is made. 2722 is the DMR ID of that Talk Group. EI4ALE is a Private Call so when the call is made it will be only directed to that individual. On completion of the contacts screen, the next task is to assign channels.
Channels
From the menu, select "Channels" and the following screen will appear
All of the positions with red arrows need to be filled in the following order
Channel Name - From our Example above, this one can be named Ireland Calling Channel
Channel Mode - Generally defaults the Digital, if not the drop down menu will allow selection
Frequency - Your Choice of Frequency for the RX and TX frequencies. The same if simplex
.
Contact Name - Click on the down arrow and all of the contacts will be displayed. Choose The Ireland Call Channel
Colour Code - Can be any number 1 -15. generally set to 1 unless otherwise required
Repeater Slot - Can be set to 1 or 2. On repeaters, International contacts on Slot 1 local on Slot 2
TOT (S) - Set to 180 secs as all networks time out after 3 mins
Power - Set to low power if using a local Hotspot or High for a Repeater
If it is planned to use the Radio with a Hotspot such as an OpenSpot or DVMega, program the simplex frequency of the device you wish to use.
It is possible to program Analog Channels for Repeaters or Simplex use. CTCSS tones can be included on Analog Channels.
Zones
With earlier set there were a maximum of 16 zones where 16 channels could be stored in each. This equates to about 256 channels. This allows one to sort specific areas into a common Zone. A Zone could be Ireland and UK contacts where all Irish and UK channels could be stored, Another could store USA channels and so on.
Zones may be selected from the menu. Click on Zone 1 in The menu and the screen shown will appear. This Zone can be renamed relevant to the channels therein. Click on Zones several times and more will be added.
Click on Zone 1 in the menu and the screen shown will appear. This Zone can be renamed by back spacing over Zone 1and giving a relevant name for the channels contained therein.
To add channels to the Zone, the available channels will be shown in the Left hand column. Click on a channel in the list as in channel 2 in the diagram which is highlighted. Click the add button in the centre of the box and the channel will be transferred into the Zone on the right hand side as a channel member.
In the case of the Tytera MD-380 there are only 16 Zones available for programming with channel members.
Now
SAVE THE PROGRAM to the computer before transferring the code plug into the Radio. It is generally best to program a few channels and try them out before adding more. Program local channels first and then move on to outside the country.
Most DMR Radios follow this protocol. It may seem laborious in the beginning but it becomes second nature after a few tries. It is really no different to using Chirp to program Analog Radios.
Operation of DMR
Once fully programmed, switch on the radio, select the Zone with the desired contact contained therein. Press the PTT and put out a call. It is normally wise to call on a calling channel such as Ireland Call or UK Call. From there one can move to a chat channel. A more complex Code Plug will have channels allocated for use on Hotspots, Gateways and Repeaters depending on the equipment in the locality.
Bear in mind that International contacts should be made on Slot 1 and Local and UK contacts on Slot 2. This will ensure free QRM free operation. Remember that calls made to Talk Group 9 may be used on either Slot as these will only be relayed locally and not routed through the Brandmeister Network.
Galway Facilities
The Galway City DMR Repeater EI7RHD operates on Input 430.450 and Output 439.450. Both Time Slots may be used. TG9 is relayed through the system in the same manner as an Analog Repeater. All Other Talk Groups will be routed through the Brandmeister Network. Talk Groups
2722 Ireland Call, 2723 Ireland Chat and 2724 YSF Ireland are programmed in as Static Talk Groups which means that any activity on any of these Talk Groups will be re-transmitted by the Repeater.
The Galway City simplex Multi-Mode Gateway EI2GCD operates on 144.850. This Gateway only operates on Slot 2. The Gateway is located on the same site as the Repeater. The operation of Busy International Talk Groups on this device is not encouraged as they tend to take over the system preventing other users benefiting from the system. It is ideal for use with Local and Semi-Local Talk Groups. Always Disconnect from busy International Talk Groups after use.
Proposed Expansion
The Galway DMR Network is due to expand with a Repeaters located on
Inishbofin Island,
Abbeyknockmoy and the
Eastern side of Loughrea. This should provide 95% coverage of County Galway with spillover coverage into neighbouring Counties.
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