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27
Understanding Scanning
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
BCD396T 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 fleet identification, and then 8 more times to
identify subfleets.
For example, the complete AFS for the Police
Department West District’s dispatch channel might be
01-062. 01 identifies the agency as the police
department, 06 identifies the fleet as the West district,
and 2 identifies the subfleet as the dispatch channel.
While these assignments are somewhat arbitrary and
vary from system to system, there are many resources
on the web for finding the assignments for most
systems. Because of the logical hierarchy of the AFS
BCD396T Paper OM.fm Page 27 Wednesday, March 30, 2005 8:36 PM