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Understanding Scanning and the BCT15
scanner. Now, the Fort Worth systems are locked out and System Quick Keys [1],
[2], and [3] allow selection between the Phoenix-area systems.
Multi-Site Trunking
Some systems covering a very large geographic area use multiple antenna sites
that each operate on different frequencies, but that use the same Talk Group ID’s
for traffic. When programming such a system, you program each site’s frequencies
and other settings into the system, then program the channels into channel groups
within that system. Each site can have its own quick key, so you can turn each
individual site on or off while you scan. Since all sites share all the channels within
the system, multi-site trunking is much more efficient than programming each site
as a separate system.
Not only does your BCT15 scan channels like a conventional scanner, it actually
follows the users of a trunked radio system. Once you know and program a talk
group’s ID (TGID), you won’t miss any of the action.
If you are a new scanner enthusiast, you might want to read the first part of this
manual and use your scanner in conventional mode before you begin trunk
tracking. Understanding scanning fundamentals and terminology will make trunk
tracking much easier. If you are already an experienced scanner operator, you can
review the programming worksheets and their associated pages in the Reference
Section of this manual.
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
All Motorola trunking systems 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 the person’s 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 speaking. This all typically takes place in
about a second...the person transmitting hears a beep from their radio when the
channel is assigned and then it is OK to start talking.