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Friday, June 08, 2018

DMR Code Plug Concepts

DMR has captured almost mainstream attention of the amateur radio community. Its value is much more clear than it was 12, 24, 48 or even 60 months ago. There is a learning curve when migrating from what is deep rooted in the community when it comes to having conversations, utilizing a repeater, sharing a "virtual frequency" or talk group and even programming a radio.



HVDN predicted that DMR would really take off when dual band hand held radios became affordable and feature rich.  With over 100,000 registered users which is almost double what it was just less than two years ago, DMR is here to stay and slowly start replacing reliable and standard FM analog based communication.

Here are some tips on getting the most out of your DMR radio.  This article is aimed at those who have already spent some time around DMR, but not expert level.  

User Contacts

Lets think of "user contacts" the same as you would a caller ID on a phone.  If your radio supports a user database such as is needed for storing all the DMR ID's, call signs, names and locations of every DMR user,  use that function!    This will allow you use the actual allocation for storing contacts for other things, such as private or group talk groups, expanded talk groups that provide access to other modes and special contacts for non voice applications such as text messaging, location sharing, weather reports and much more. 

Popular radios that support a User Database function include the MD-380 series, MD-2017, HD1, MD-UV380, AT868, and a few others. Radios like the GD-77 are more basic and not as fully capable when it comes to user database management.

Having the database of users stored in your radio provides identity information about other users which is great, especially when using non repeater or  point to point communication known as "simplex".

Receive Groups

Repeater or hot spot use is slightly different when it comes to receive groups. A receive group allows you to store multiple talk groups and assign it to a specific memory channel in your radio. This is like having the ability on an FM analog radio to store multiple PL tones in one memory channel. A receive group essentially acts as a slightly wider filter mechanism so you can listen to users of a channel from multiple talk groups, but just one at a time.  This function allows you to leave your radio on one memory channel and not have to physically change channels.  Many radios that have this feature can also let you set a default talk group to always transmit on or user the last heard talk group only. This flexibility allows the user to program fewer channels in a a radio compared to many. 

Here is how it would look in a standard configuration if you selected one talk group per channel on a local repeater and this may be how a repeater owner may tell you what is carried on the his/her repeater.



If you set your radio up using receive groups, you can shrink from 16 channels to much less. Here is an example:


On channel one, this would default to transmit on TG 8888, but receive all listed TG. If set up, it can also transmit on the last heard TG instead of TG 8888.  Channel two works the same way, but just for the TG on TS 2.

Channel 3 is for just the three TAC TG since they are all on TS 1, but channel 7 and channel 8 are set up for just TAC 312 on its own and for TS 1 and TS 2. No other TG can be received when on these channels.

Channel 4 is for a local TG that the repeater owner does not let traffic go out over the internet, so can only be used locally, but the receive group also includes 2, 9 and 312 as well which gives some internet connected TG along with non-internet connected TG.

Channel 5 is for two TG that seem more content focused compared to general chit chat or geographically or local only focused. This may be good if there is a scheduled net on a repeater.

Channel 6 is just TG 31368 which is an internet connected TG but for a generally local area in NY, but the receive group also includes TG 8888 which is not internet connected

There is a lot of flexibility in setting up a radio using receive groups in ways such as this.

Scan Lists

Scan lists are very different than a "Receive Group"  A scan list allows multiple channels to be added to a list and scanned in order, only stopping on one when there is activity.  If there are channels with receive groups attached to them, you can create one channel called "scan all" that would look at channel 1 and channel 2 in the above 8 channel plan and be able to receive all traffic when on that "scan" channel.  You could also set it up to allow transmit on the last heard TG.  This way with one channel, you can receive anything from either time slot on the repeater and reply to what ever the last heard TG was.

Using Non-Voice Features

Much of the same logic above can also work with a hot spot user, dependent of course on how they set static talk groups up on the one time slot a hot spot is capable of operating on, which usually is TS 2.  Here is how you can set up channels for specific tasks that are not 100% voice related.

TG 310999 is often used for routing GPS location data to and from the internet to other users or applications.  TG 262993 is used for weather reporting. Many repeater owners do not want to mix voice and data applications, so lets imagine a second repeater that only carries these two talk groups plus two others, one for internet voice (TG 31368) and one for local voice (TG 8888). Consider these two additional TG more as back up capacity for a certain area to the other repeater we have created in the channel table above on 449.125 MHz.

The second "data oriented" repeater would be on the frequency of 427.505 MHz output with a 437.505 MHz input.



This second 427.505 MHz repeater would let users on TG 31368 talk to those on the 449.125 MHz repeater since TG 31368 is internet routed.

If the two repeater owners cooperated and linked TG 8888 to still only be NOT internet connected but locally networked together, users on both repeaters could use TG 8888 and cover a greater area not normally possible with one repeater.

Perhaps at some later date, the 427.505 MHz may wish to add fifth channel to permit only local activity on TG 9, but would only be on that repeater and not the 449.125 MHz.  This would then let both repeaters have local only use, local but intern-connected use via TG 8888 and internet connected use on TG 31368 for out of area contact

If a user on this 427.505 MHz repeater wished to request a weather report after following instructions in this HVDN article or this one, they can do so without affecting other voice users who normally use the 449.125 MHz repeater.

Combining What We Learned

Its possible through the use of receive groups and scan lists to do some amazing things you can not do with analog FM radios and repeaters. Here is one of them:


The above table combines two different repeaters and allows the user to listen to traffic on both of them at the same time by using channel 16, respond to voice calls on the 449 repeater and also send and receive location data on the 427 repeater.  

There are many combinations to be used in thinking about DMR this way and to do a lot with very few memory channels even in one zone.

If you have some creative code plugs you would like to share, please contribute to our database or comment with some tips below.


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