Sunday, April 21, 2019

DMR Tip 02 - What Time Slot Should I Use?


I’ve had a few people ask me what “time slot” (TS) they should use when setting up a talkgroup on a particular repeater.  For DMR Tip 02, I'll focus on answering this and give you links for more information on finding repeaters and configuring your radio correctly.

Here is a good description of what a time slot is by  NEDECN:
With a TDMA (time division multiple access) system like DMR, the mobile or portable radios are synchronized typically by a repeater and assigned a time slot. In DMR Tier 2, there are two time slots, i.e. 2-slot TDMA. A mobile radio transmits for 30 milliseconds and then receives for 30 milliseconds. It listens for a permission to transmit and then begins a call to all other talk group members who will also receive on that same time slot, e.g., Time Slot 1. Meanwhile, a different group of users on another talk group could be using Time Slot 2 simultaneously. Well almost simultaneously, offset by 30 ms., but you would never know the difference, because two voices can come out of two radios simultaneously from the same repeater.


A couple more terms before we begin:

Static: The talk group (TG) is always locked / subscribed to by the repeater.  Example, The San Diego Hangout (310014) is static on Miguel, but not on the Papa repeaters.  So if you tune in, you don’t need to do anything because the repeater is always subscribed to the TG and repeats out any traffic on it.

Dynamic:  The group is added to the repeater as soon as you press transmit for a TG that doesn’t already have the TG on it.  The TG stays on the repeater for 15 minutes.  The timer is reset if it hears anyone transmit into the repeater again on that talkgroup.  This is why “kerchunking” is acceptable and expected on DMR repeaters.  So if you are just listening to a dynamic talkgroup and then it disappears all of a sudden, just kerchunk the repeater with that TG again.

Dynamic groups are super cool and the real power of DMR in my opinion.  For example, I have the Qualcomm DMR repeater channel setup for the hangout (310014) so I can use it in my area.

What TS should I use?

The normal time slot (TS) to use for dynamic groups is TS1. 

Take a look at area 3 on the graphic below (click on it to enlarge).  This repeater page tells you what groups a repeater has as static so that you configure your radio correctly…. That is, if the group you want is static (the lock icon) on TS2, make sure you use TS2 on your channel config so that you don’t cause the repeater to subscribe to it twice.

Example:  If you use the Papa DMR repeater on Woodsen look HERE.  You’ll see that the SoCal talkgroup is static on TS2.  If you use a repeater that doesn’t have SoCal static, the normally accepted practice is to use TS1 for that dynamic group.  You’ll notice that they remind you of that at the top of the repeater page.


Brandmeister Repeater Page Details

The “Slot details” (Section 3) shows what talk groups the repeater is currently subscribed to on each time slot.  The most important thing to pay attention to are what talkgroups are “static” on this repeater.  Static groups are setup by the repeater owner and are always repeating any traffic heard on that talk group on the indicated timeslot.  Static talkgroups have a small padlock icon on them.  If you can't see them, click on the image for a larger version.

This section also shows “dynamic” talkgroups.  Instead of a lock, they are a different color and have what looks like a lightning bolt on them.  These are talkgroups that users have forced the repeater to subscribe to by transmitting to the talkgroup on the repeater.  The talkgroup is active on the repeater for 15 minutes after the operator transmits.  The expire time is reset each time an operator transmits on the talkgroup.  These talkgroups are temporary and will go away after 15 minutes if a ham operator doesn’t use it within 15 minutes.  So if you want to monitor a talkgroup that isn't static, you need to kerchunk the repeater on that talkgroup a minimum of every 15 minutes if there are no other users of that on that repeater.  (Kerchunking is OK on DMR)

On our example below, this repeater’s Timeslot 1 has the San Diego (310670) talkgroup static, and the San Diego Hangout (310014) dynamic.  I caused the 310014 to be added to the repeater when I used it while writing this post.  Timeslot 2 has the CA (3106), Southwest (3176), SoCal (31066), and USA (31606).

[Notice how hovering the mouse cursor over a timeslot can display the name.  If the timeslot is dynamic, it also displays how much longer the talkgroup has before it expires unless it is used by someone]

NOTE!
If you plan on using a particular talkgroup on a repeater, check to see if that talkgroup is static on that repeater.  If so, make sure you use the same timeslot as shown on the configuration page.  For example, if you plan on using the CA talkgroup (3106) on this repeater, be sure to configure your radio to use Timeslot 2 when using this repeater.  
You’ll notice that the PapaSystem repeaters all have the CA talkgroup on Timeslot 1.

If you want more detail on all of the repeater info, see this article.

I hope you found this tip useful.   Please use the comments section to submit your questions.

73,
N1CLC
Christian Claborne
(aka Chris Claborne)

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