FCC Station Class Codes
From The RadioReference Wiki
The description of an FB8 prior to 10-04-2010 is incorrect. An FB8 is the designation of a centralized trunked radio system operating between 150 - 470 MHz with exclusive use of the frequency within its area of operation. It is paired with MO8 station class to indicate subscriber units. FB2 is used to designate centralized trunked repeaters above 470 as these frequencies already have geographic exclusivity (assuming loading has been met).