SmartTrunk Systems SmarTrunk II, System Overview, Page: 7 / 57

7
SmarTrunk Systems, Inc.
Rules Regarding VHF and UHF Trunking in the United States
The FCC has authorized the use of “centralized” trunked systems for
VHF and UHF frequency bands
where at least one frequency must have
a Protected Service Area (PSA). This frequency is identified with a station
class designation of FB8 for the Repeater. While FB8 codes are used only
with trunked (YG or YW) systems, an FB8 frequency may not be used for
conventional systems.
Centralized trunking refers to trunking systems that use dedicated
(exclusive) control channels for data communication between the
mobiles and the trunked repeaters. In such systems, the mobiles
constantly monitor the control channel for channel assignment
instructions. When a group call is initiated, the trunking controller
transmits instructions telling the mobiles in the group to switch to a
voice channel assigned for that conversation. Thus, the “brains” of the
system are in the system controller at the repeater site.
Most trunking systems such as MPT-1327, Motorola’s Smartnet, E. F.
Johnson’s LTR. Trident’s Passport, etc are centralized systems. As they
are designed to use clear frequencies, these trunking formats are not
as well suited as SmarTrunk or as easy to license at VHF and UHF
frequencies because of the lack of exclusive channels in those bands.
To get around this problem, the FCC requires potential centralized
system operators. . . “to obtain some form of exclusivity in their
respective service areas”. This requires the operator to obtain written
permission from all other licensees within a 70 mile radius of the
proposed base station, similar to the FCC rules for telephone
interconnect in major metropolitan areas. However, due to the
frequency congestion in these bands, this requirement is extremely
difficult to meet. All other users on the proposed trunked channels
and
immediately adjacent channels would have to agree to convert to trunked
operation. Since, by definition, centralized trunked systems require
exclusive channels, the other affected users would have to agree to a
simultaneous conversion of their radio systems, which would require
scrapping their conventional equipment and purchasing all new mobile
radios.
1 • Things you always wanted to know about trunking…