User Guide

DMO Mode
In Direct Mode Operation (DMO), radios communicate directly with other
TETRA radios without using a network. The radios must all switch to DMO
and select the same talkgroup, and that talkgroup must use the same channel
(frequency). Communications to other users on the network are impossible
unless they also switch to DMO and select the same talkgroup.
Note: This means that in DMO, communications to the dispatcher is
impossible unless they also switch to DMO and select the same talkgroup,
or if they communicate through a DMO gateway (see DMO gateway
operation on page 1).
Group calls
DMO supports group calls (see Group calls on page 62) which are made and
received in the same way as radios operating in TMO. In DMO TETRA Alarm
Calls are either sent to the currently selected DMO talkgroup or (if
customised) may switch to TMO to make the call. If TMO is unavailable
Alarm Calls are made using DMO. See Emergency operation on page 33.
Individual calls
Your radio can be customised to allow you to make individual calls to other
radios working in DMO which are attached to the same talkgroup. In this
case individual calls are initiated by pressing the PTT key. See Making
individual calls (half-duplex mode) on page 64. (Individual calls to radios which
have selected different DMO talkgroups are prevented unless the DMO
talkgroups have the same carrier frequency.)
Your radio can also be customised to allow you to select a channel only
talkgroup. If you select a channel only talkgroup your radio cannot make or
receive group calls: it can only make or receive individual calls.
Tip: You can enable Presence Checking so that your radio checks
whether the receiving radio is available to receive when you attempt an
Individual call. See DMO options on page 90.
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SC20 series – 04/2016