As with mobile FM, there are also Digital Repeaters for DMR. They can be used in a similar standalone way to FM repeaters, or they can be linked together to form a network of repeaters by commands sent from a DMR transceiver or DMR handheld radio.
A major difference between a Digital Repeater and an Analog (FM) repeater, apart from being linked to the internet, is they support two simultaneous QSO’s at the same time. That is two repeaters in one. This is achieved by the digital signal from the repeater being divided into two time slots.
This is why you must tell the repeater which slot you want to transmit /receive on, Slot 1 or Slot 2.
Similar to the function of CTCSS for FM repeaters a colour code system is used for Digital Repeaters, except it is not a colour it’s a number between 1 and 15.
The digital repeaters in a country are linked via the internet to a Master Server which can be looked upon as a central telephone exchange. However there are a number of different digital networks each with its own Master Server. Normally a repeater will only be connected to one of these networks.
The Master Server connects to Master Servers in other countries, of the same network, to form a Global Network. For instance, a repeater in Bracknell is able to be connected to one or more repeaters in the USA, or just to all the repeaters in the South of England.
Like a Net of two or more Amateurs can be set up on a specific frequency, the digital repeater can be set up to listen out for a particular network of Amateurs known as a Talk Group (TG). This is really a network of repeaters listening out for an Amateur requesting connection to a specific TG (Net)
For example: on the Brandmeister network, TG2350 is a Net which will broadcast to all the repeaters in the UK. So if you send TG2350 from your radio to the repeater you are connected to (and it is a Brandmeister Repeater) your call will be transmitted from every repeater on the Brandmeister network in the UK, unless it is active on another TG at the time, or not programmed to listen out for TG2350 calls. So on one repeater you could have a local Net on TG9 slot 2, and another Net on TG2350 slot 1 involving Amateurs across the whole of the UK.