Trunking Operation; Types Of Trunking Systems - Radio Shack PRO-94 Owner's Manual

TRUNKING OPERATION

The PRO-94 scanner tracks transmissions that use the
Motorola Type I, Type II, hybrid, and, Ericsson EDACS
analog trunking systems. Remember these important
points when tracking transmissions:
• Your scanner cannot scan trunked system and
conventional frequencies at the same time.
• The frequencies for many of the 800 MHz, 900
MHz, and EDACS public safety systems are listed
in the separate "National Public Safety Trunked
System Frequency Guide" included with your
PRO-94.

TYPES OF TRUNKING SYSTEMS

This trunking scanner monitors two basic types of sys-
tems — the Motorola Type I/Type II or hybrid System,
and the Ericsson EDACS System. 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 their PTT (push
to talk) control. Thus, trunking systems, in general, allo-
cate a few frequencies among many different users. Mo-
torola Type I and Type II systems achieve the same
thing in a slightly different way. One important distinction
between these systems is the amount of data transmit-
ted by each radio when the operator pushes the PTT
control. A Type I system, transmits the radio's ID and its
current affiliation or the trunk system to which it belongs.
A Type II system only transmits the radio's ID.
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 four fleets, each with eight subfleets.
41