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Types of Trunking Systems
Trunking systems divide a few frequencies among
many different users, but the way that each system
does this is slightly different. This section describes
some of the technical data behind Motorola, EDACS,
and LTR trunked radio systems.
Motorola Trunking
While there are different types of Motorola trunking
systems, they all use the same basic trunking method.
The system consists of one control channel (or as
many as 4 per system but only one is active at any
one time), plus one or more voice channels (typically
10, 20, or 28 total channels). When a user presses
Push To Talk (PTT) to transmit, their radio first sends
their talk group information to the control channel.
The computer then assigns that talk group to a specific
voice channel and transmits that data over the control
channel. All radios in that talk group switch over to the
assigned voice channel and the user can begin speak-
ing. This all typically takes place in about a sec-
ond...the person transmitting hears a beep from their
radio when the channel is assigned and then it is OK
to start talking.
The systems in use are:
Motorola Type I – the radios send the radio ID, the
fleet and subfleet talk group ID to the control channel
each time they transmit. To program a Type I system,
you need to know the system’s fleet map. The most
common fleet maps are included in “Preset Map 1 Pre-
set Map 2” on Page 133. You can also find fleet map
resources on the web.
Motorola Type II – the radios only send the radio ID
and radio channel code to the control channel. The
central computer keeps a database of radio ID’s and
which talk group is assigned to which channel code for
each radio, so with this system the user’s radio sends
only about
1
/3 the data as a Type I system with each
transmission. Type II systems do not use Fleet-