We had a few people ask about some of the underlying mechanics of DMR networks as well as the differences between using DMR on repeaters vs. hotspots. This is a topic that has many different facets and, as such, is something that will be covered across multiple articles.
Ferrell Brown (KE4QDC) was kind enough to send me a link to an article written by Daniel Moses (K9NPX - Farmer City, IL) that does a great job of covering why certain considerations need to be taken into account when using DMR.
Pay special attention to the "3 talk 3 rule". :-)
This post is to help those new to digital and DMR get started
By Daniel Moses - K9NPX
So I'm a fairly new HAM and fairly new to digital. There's definitely a bit of a learning curve but it pays off in the end. Once you learn digital you can easily work contacts around the globe. I got my ticket about two years ago but haven't used it much until I recently discovered digital. I'll go over some of what I've learned and hopefully help others get on the right talkgroups and make some good QSOs.
Radio etiquette is a little different for DMR. It's usually bad practice to key up a repeater and not say anything. However this is required with DMR. When making a call you want to key the talkgroup once to make sure it's linked then wait a few seconds to make sure the talkgroup is clear before you transmit so you don't talk over an existing conversation.
The 3 talk 3 rule
Unlike analog, digital has a buffer. Transmissions tend to get cut off at the beginning and end if you don't follow this rule. Basically you want to key the radio, wait 3 seconds and then start to talk. You also want to wait a few seconds after you're done talking before you un-key the radio to make sure your transmission doesn't get cut off at the end.
Talkgroups are group calls, think of them as chat rooms. Once you're connected to a talkgroup you can hear all conversations on that channel. Talkgroups are generally split up by location. 91 is Worldwide, Nationwide 3100 is North America, 3169 is Midwest, 3117 is Illinois and so on. There are lots of other talkgroups for different groups as well TGIF, The Guild, TAC 310. There are over 1,000 talkgroups available on Brandmeister. The Pi Star website has a nice lis here.
There are other networks but Brandmeister seems to be the most used. The Brandmeister servers route calls between repeaters and hotspots. Repeater book will usually tell you if a repeater is Brandmeister linked and what static talkgroups it has. Static talkgroups are talkgroups that are always linked however if someone is using a different talkgroup on the repeater or hotspot you will not hear traffic from the static talkgroups. After a set amount of time it will usually revert to the static talkgroup.
Repeaters vs Hotspots
Once you have a hotspot properly setup there is little difference between using it vs a repeater. The main difference is that when on a repeater you have to keep a watch for other users and share the repeater. Here's a list of things to know.
Even if there is a statically linked talkgroup if another talkgroup is in use it will override the static talkgroup so always make sure you key up once and listen for other traffic before starting your transmission. If the channel is clear you can then announce your callsign or any other transmission you wish to make. Remember to pause before and after your transmission. To use a dynamic talkgroup just select it in your radio, key up and listen for traffic. Most repeaters have a timer for dynamic talkgroups and will return to the static talkgroup after so many minutes of inactivity.
Just remember to be polite and practice good operating procedure and you'll be talking around the globe in no time. A few good places to start are
Hope this helps you get going, 73s K9NPX
A few points to add to Daniel's article:
"Hotspots only use one time slot"
That's not entirely valid anymore. There are several duplex MMDVM boards on the market (i.e. N5BOC and Zumspot) that allow for two timeslots. You can have a static talkgroup configured on timeslot 1 and another static talkgroup on timeslot 2 and they will never interfere with each other. And the MMDVM boards used in repeaters (i.e. RepeaterBuilder.com's STM32) support duplex.
Brandmeister does not care about which talkgroup you want to connect to from your hotspot, nor do they care about which timeslot you use to connect to any of the talkgroups.
Repeater operators have a challenge that many hotspot users do not recognize in that their services are consumed by a larger population whereas a hotspot user only has to be concerned about their own use. In reality, there are only two timeslots available on a repeater. When both timeslots are in use, then it doesn't matter how many talkgroups you can connect to, there's no way for others to use the repeater. Owners have to balance availability and usability. It's something a lot of hams don't like but it's a reality that must be addressed.
Case in point, one of the local repeater operators has their repeaters are connected to Brandmeister. They use an MMDVM board designed for use in a repeater in conjunction with a pair of Motorola mobile radios (GM300 radios if I recall correctly). A while back, they had someone that thought it would be fun to key up on TAC310 on both timeslots. That individual would key up on TAC310 on timeslot 1, then key up on TAC310 on timeslot 2. As soon as the inactivity timeout was about to expire, they simply keyed up TAC310 on timeslots 1 and 2. Guess what? That created a condition that is referred to in the security world as a "Denial of Service". If you wanted to use another talkgroup when this person was having their fun, then tough...you couldn't.
That's not a good experience!
My understanding is the operator reached out to the person and asked them to stop - thankfully they did.
By default, repeaters that are connected to Brandmeister also don't care which talkgroup you want to use, nor which timeslot you use. I don't feel that it's safe to assume that automatically applies to ALL repeaters on Brandmeister.
Case in point, I was in Las Vegas earlier this year and wanted to use my DMR radio to connect to the Georgia talkgroup so I could participate in the net. Despite there being several DMR repeaters connected to Brandmeister, there was only one that would allow me to connect to Georgia TG 3113 and I could only do so on one of the two timeslots.
Many repeater operators use an additional piece of software that allows them to whitelist the talkgroups they allow. It's extremely common to find repeaters that restrict which talkgroups you can use and which timeslot you can use them on.
You can read more great content from Daniel on his website:
Jeff Hochberg - W4JEW