Radio Shack 20-521 Scanner User Manual


 
39
TRUNK TRACKING
Your scanner is designed to track transmissions on Mo-
torola Type I, Type II, and hybrid analog trunking sys-
tems, which are extensively used in 800 MHz
communications. Remember these important points
when tracking transmissions:
Your scanner monitors Type II systems by default.
However, you can change this if the system in your
area is different (see “Types of Trunking Systems”
below and “Scanning Type I and Hybrid Trunked
Systems” on Page 50 for more information).
Your scanner cannot track transmissions on non-
Motorola trunking systems.
Your scanner cannot track an 800 MHz trunked
system and scan conventional frequencies at the
same time.
The frequencies for many of the 800 MHz public
safety systems are listed in the separate “National
Public Safety Trunked System Frequency Guide”
included with your PRO-91.
TYPES OF TRUNKING SYSTEMS
Your trunk tracking scanner can monitor two basic types
of systems —
Type I
and
Type II
. Instead of selecting a
specific frequency to transmit on, a trunked system
chooses one of several frequencies in a 2-way radio us-
er’s talk group when that user presses PTT (push to
talk). Thus, trunking systems allocate a few frequencies
among many different users, but the way Type I and
Type II systems do this is slightly different. One impor-
tant distinction between these systems is the amount of
data transmitted by each radio when its push-to-talk
(PTT) button is pressed. In a Type I system, the radio’s
ID and its current affiliation (the trunk system it belongs
to) are both transmitted. In a Type II system, only the ra-
dio’s ID is transmitted.
Why the difference? In Type I systems, each radio in
the trunk group individually transmits its own affiliation,
while the trunk system maintains a database that deter-
mines each radio's affiliation(s) in Type II systems.
Another difference between the systems is that Type I
systems are arranged in a fleet-subfleet hierarchy. For
example, it is possible for a city using a Type I system
to designate 4 fleets, each with 8 subfleets.