Slots and talk groups

One of the great advantages of DMR is its ability to support two simultaneous conversations on one repeater using Time Division Multiple Access (TDMA).  The two slot TDMA system is unique in amateur digital modes.

Our DMR network has many talk groups spread across the two slots.  Some of these are static – i.e. always on, and some are User Activated (UA) – they need to be keyed (“kerchunked”) up, and time out after a period of inactivity (normally 15 mins).

You can see the static groups on the IPSC server web page:

The static groups are shown in the 5th and 8th columns alongside each repeater.

There are a lot of talk groups, and they can be confusing.  They are described at

Network loading

Although the network is quiet during the day, the user base has increased significantly (and continues to do so), so there will be occasions where there are two, sometimes three groups of users trying to use both time slots.

When user numbers were low, it didn’t really matter if you used a static talk group, but these days, a static group can hold up a time slot and make the network difficult to use for others. 

This is particularly the case with the State based 380x series talk groups on time slot 2.  If two stations are talking on, say, 3802, it locks the slot onto 3802 for all VK2 repeaters – other VK2 users are unable to use the main calling talk group – 505.

Whether you are accessing the network via a repeater or a hotspot, you should use talk groups that key up the minimum number of repeaters if you wish to chat with another station after QSY’ing off 505 – this will ensure that the maximum number of users can access the network.

If you are working a station on the same repeater, use TG9 on time slot 1 – this only keys the one repeater on one time slot.

If you are using two separate repeaters, switch to a UA talk group.  Most UA talk groups are on time slot 1, but there is one available on slot 2: TG3800.

As with all UA talk groups, TG3800 only connects the repeaters used in the contact – this keeps the other repeaters free on time slot 2 for stations to call on the main VK calling “channel”:  TG505.

UA “chat” talk groups are listed below:

TG53 TG3800

*3810 is intended for WICEN but is available for general use outside WICEN activities.

If possible, it is always handy to have the IPSC server web page running on a PC/tablet/phone – this gives you an overview of network activity.

TG5 on time slot 1 is a special case – it is intended for national broadcasts and nets, so is intentionally static.  It should not be used for other traffic.