I will attempt to break down these concepts and place them into real world scenarios, in the hopes that future operators can read and understand how they work. I am not a DMR expert, but I am a big fan with some decent experience in the mode and some great teachers.
About me - I own and operate a DMR repeater in the state of Michigan, a Motorola XPR8300 running on UHF. I'm one of the NCS for the MichiganONE Statewide DMR Net and have a dozen or so DMR radios. I've had the pleasure of traveling around the state to give presentations on DMR and why it's the best mode in amateur radio hands down.
First of all, it's important to understand that the concept of dynamic or static talkgroups exists only within the scope of a repeater or hotspot. From here forward I will generally refer to these as just repeaters but understand it's interchangeable. Anything I discuss about repeaters is also applicable for your personal hotspot, which is just a mini repeater of sorts. This goes without saying, the concept of D & S is not applicable for simplex operation.
Second of all, it's equally important to understand that the availability of a TG (e.g. dynamic or static) is simply how it's configured on a repeater. In other words, the concept of a dynamic vs static has to do with HOW and WHEN a talkgroup is active on a repeater. It does not have any bearing on how an operator transmits to a TG, just on when they can hear a TG on a repeater. We will however discuss later the impact that has in the context of transmitting.
• Refers to how a TG is configured on a repeater
• Only pertains to how the operator receives TG traffic
A static talkgroup is one that is "always on / always active" on a repeater. This means that if a TG has traffic, your repeater or hotspot is transmitting that outward for you to receive. These cannot be turned off by users, and requires the repeater admins to make changes. This has several uses, namely as a way to link several repeaters together to form a wider area network, or to signify a TG has some kind of importance to a repeater.
The alternative to static, a dynamic talkgroup is one that is "user activated". It will not be active until a user selects the TG channel on their radio and "keys up", thus initiating traffic. This TG will now be active, but only for a limited time. Generally speaking, a dynamic TG is active for 15 minutes from the last time a user keys up or until a user sends a disconnect code over the air. It's important to note, if you are having a QSO on a TG that has been dynamically activated, it will not time out until you stop transmitting - that's when the clock starts ticking.
It's also important to note that a repeater can have multiple dynamic TG's activate at any one time. In theory, you could have 10 dynamic TG's active at the same time, although I don't recommend this. In this scenario, the repeater handles traffic in a first come, first serve manner. This can lead to traffic being missed as each timeslot can only transmit traffic from one TG at a time - the other 9 are out of luck.
As an example for how these work in a practical setting, I'll use my DMR repeater. As it's currently configured, it has Michigan Statewide (3126) as a static talkgroup on TS1, and extended local traffic on TS2. If there is any activity on either of those TG's, it's always transmitted from my repeater. I also allow for users to dynamically activate any BrandMeister talkgroup they would like on TS2.
This means that what I deem as the most important TG's to have (the statewide TG and the local TG) are always on the repeater BUT if a user would like to activate US Nationwide or Worldwide they are absolutely able to do so on TS2.
Now that you (hopefully) understand the difference between static and dynamic, let's discuss what that means for you as an operator looking to join into a QSO or call out on a TG. This is critical - regardless of a TG being static or dynamic YOU MUST HAVE THE TG CHANNEL SELECTED ON YOUR RADIO! Just because a TG is static, does not mean any traffic into the repeater on the timeslot is routed to the talkgroup. Every single transmission on DMR requires a target TG, meaning the channel of your radio must match where you intend to transmit.
Let's walk through a real life example to help illustrate this. Let's say your local repeater has TG91 set as a static talkgroup. As you are listening to this, you hear a QSO you would like to join. You pick up your radio, and notice the channel is set to TG3100. If you were to key up and announce your call sign, you would be speaking on, YOU GUESSED IT, TG3100 and NOT 91 as you intended. You would have to change the channel on your radio to TG91 and THEN key up.
(D-Star trigger warning) This is much different than D-Star or Fusion, in that if a repeater is linked to a reflector or room, any traffic into the repeater goes to said reflector or room. DMR absolutely does not work in that way - every single time you press the PTT button traffic is routed to the channel talkgroup on your handset. Period.
You Made It!
I'm sure I've missed something here, so I reserve the right to edit this post as needed to correct some stupid mistake I've made. Other than that, if you have question please don't hesitate to ask as I'm sure myself or someone else on here would be happy to help you out.