User's Manual
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
might want to go to Trunk Tracking on page 38 now.
Trunked Scanning
While conventional scanning worked great while there were only a
few groups wanting to use the frequencies, with the advent of
smaller, lower-cost radios more and more agencies and businesses
wanted to take advantage of the utility of 2way radio. As a result,
the bands that were used most became full, so new users were not
able to take advantage of the technology as quickly as they wanted.
Trunking solved this frequency shortage by allowing multiple groups
to use the same set of frequencies in a very efficient way. While
each type of trunking system operates a little differently (see the
next few sections), they all work on the same basic premise: even
in a system with a lot of users, only a few users are ever
transmitting at any one time.
Instead of being assigned a frequency, as with conventional
systems, each group is assigned a talk group ID. A central
computer controls the frequency each group operates on...and this
frequency selection is made each time a user transmits. So, while
on a conventional system queries, replies, and follow-ups are all on
a single frequency, they could each be on completely different
frequencies on a trunked system. This semi-random frequency
assignment made monitoring such a system impossible prior to
Uniden’s invention of the Trunktracking scanner.
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.
There are really two basic types that are important when using your
TrunkTracker™ scanner. These are usually referred to as Type I
and Type II systems.
One important distinction between these two systems is the amount
of data transmitted by each radio when its push-to-talk button (PTT)
is pressed. Every radio in a trunked system is assigned a unique ID
so the central site computer can identify it when it’s used. Both
Type I and Type II systems place radios (or radio users) into
groups, called talk groups, and these talk groups are also assigned
unique IDs. Some radios have access to only one talk group, while
others have access to many talk groups. Which talk group(s) each
radio can access is called the radio’s affiliation(s).
In a Type II system, when someone uses their radio, only the radio
ID is transmitted when PTT is pressed, whereas in a Type I system
the radio ID and its current affiliation are both transmitted when PTT
is pressed.
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