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26
Understanding Scanning
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 Fleet
Maps” on Page 129. 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-
subfleet talk groups; instead they use a 5-digit ID for
each talk group.
Type IIi Hybrid — these systems support a mix of both
Type I and Type II users. Like Type I systems, you
must know the system’s fleet map to ensure proper
tracking.
Motorola ASTRO 25 (APCO 25) – these radios are
similar to Type II systems, but send only the radio ID
and radio channel code to the control channel, trans-
mitting voice in digital form.