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Each individual channel serves as a control channel for the users
and user groups that are "homed" to that channel by sending out
a subaudible data message simultaneously with voice traffic
when needed.
The portable and mobile radios in a distributed control trunked
radio system monitor their home channel when idle for data
messages that include commands regarding activity for their
talkgroup, and, in the event that the home channel is busy, a free
channel elsewhere on the system that is available for
communications if needed.
When a user in a distributed control system needs to speak, they
press the push-to-talk button on their radio. If the home channel
is not in use, the controller sends a data message out over the
home channel that tells the other users in the talkgroup that a
call is taking place on the home channel, and all the radios in the
talkgroup transition to voice call mode on the home channel.
If the home channel is busy, it sends subaudible data messages
over the home channel simultaneously with any voice traffic it is
carrying. These subaudible data messages include a "free
repeater" message that informs other radios homed to the
channel of the next available free repeater that is not in use.
When a user places a call by pressing the push-to-talk button in
this scenario, the new call is placed on this free repeater, and the
subaudible data message on the home is updated to include
signaling that tells other users of the talkgroup that the talkgroup
is now active on the free repeater. The other users switch to the
free repeater and the voice call proceeds there.
LTR systems operate using distributed control. Your scanner
utilizes the data sent by each controller on each channel to track
the activity on an LTR system.
PSR-600 User Manual
Page
127
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