Repeater System/Frequencies & Talk Groups

The DMR repeater system provides amateur radio operators access to a commercial level radio network whose operation is based on talk groups rather than just frequency channels.  Talk groups are unique digital identifiers that help route conversations through the network and into the user’s radio.  DMR repeaters support two simultaneous voice/data conversations on a single frequency pair.  Each repeater is configured to support a full time local talk group and a wide area talk group.  During normal operation, the SCHEART DMR network is integrated with the NCPRN network and the wide area talk group (PRN) covers South Carolina, North Carolina, parts of VA and Texas.

To support two simultaneous conversations on the same frequency, the repeater uses Time Division Multiple Access (TDMA) technology. With TDMA, conversations are divided into two time slots and the radio/repeater synchronizes their data depending on which time slot used.  In normal operation, SCHEART DMR is configured to support a local talk group (time slot 1) and a wide area (PRN time slot 2) talk group. Stations on the local talk group hear only local traffic while stations on the PRN talk group will hear any traffic on the multi-state network during normal operational mode.  Additional talk groups are available that share time slot 1 on a dynamic basis.  If a user keys one of the dynamic talk groups, that talk group shares time slot 1 with local.

Operationally, stations should use the Local talk group for all local conversations.  The PRN talk group activates over 60 repeaters and is for initial contact and should be used only for short conversations. If you make a contact with a station on PRN and plan to have an extended conversation, both stations should switch to a Chat talk group.  Two Chat talk groups are provided: Chat 1 and Chat 2.  These are dynamic talk groups that do not have any repeaters connected full time.  Only stations that activate the Chat talk group through a repeater will be connected.  Two stations may move their conversation from PRN to a Chat talk group or multiple stations may move.  In either case frees up the PRN channel. When finished, select the Clear Timeslot channel and key your transceiver.  This action will cancel the talk group on the repeater.  If you fail to clear the time slot, the connection automatically times out after 15 minutes with no traffic on the local repeater.  Echotest is dynamic talk group that allows testing of your radio audio but is only active for 1 minute. There  is no need to issue a Clear Times Slot command after using Echotest.

SCHEART DMR has two operational modes: Normal Operations and Emergency Operations.  During Normal Operations, all talk groups are available to stations and the PRN talk group covers multiple states.  SCHEART also has a special talk group called SC Call.  This talk group only operates on the SCHEART network.  When using this talk group, key and make your call.  Every SCHEART repeater not currently carrying a conversation on Time Slot 1 will broadcast your transmission.  SC Call talk group is to establish an initial contact within the state.  Please move any extended conversation to Chat 1 or Chat 2 so you do not time up all 30 SCHEART repeaters.

During exercises and incident responses, the DMR system may revert to emergency operational mode (EOM).  Under the EOM, the PRN talk group is restricted to only SCHEART repeaters.  The Local Talk Group is not affected but normal dynamic talk groups outside the state are suspended.  Additional talk groups to support mutual aid communications are activated along with a data channel.   Other talk groups may be established by the network administrators as necessary to support the response.  The DMR system will remain open but stations supporting the incident should be provided priority access.  The following two tables describe talk groups in both modes:

Normal Operational Mode:

Emergency Operational Mode

* PRN wide area traffic restricted to repeaters within SC.

** Dynamic PTT group

SCHEART  DMR Repeater Information – All repeaters use Color code = 1

” Denotes a SCHEART partner repeater