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25
Understanding Scanning
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.
EDACS Trunking
EDACS trunking works in much the same way as
Motorola trunking with a couple of major differences.
In an EDACS system, each frequency used by the
system is assigned a Logical Channel Number (LCN) so
that less data needs to be transmitted by the control
channel. Also, talk groups are assigned in an Agency-
Fleet-Subfleet (AFS) hierarchy. Also, there is one
variation of EDACS called SCAT that your BC246T can
monitor.
Logical Channel Numbers – each frequency used by the
system is assigned an LCN. This information is
programmed into each user radio. When a user presses
PTT, their radio sends their AFS information to the control
channel. The computer then assigns that talk group to a
channel and sends the LCN so that all other radios in that
talk group will switch to the correct channel. To program
an EDACS system in your scanner, you will need to know
both the frequencies used by the system and the LCN for
each frequency.
Agency-Fleet-Subfleet – talk group ID’s for EDACS
systems are assigned in a way that makes it easy to see
at a glance the affiliation of the user. Each radio is
assigned a 2-digit agency identifier from 00 – 15.
For example, 01 might be used by the police, 02 by
ambulance service, 03 by the fire department, and so on.
Each agency is then subdivided up to 16 times to provide