Federal Bureau of Investigation
From The RadioReference Wiki
The FBI radio system is encrypted most of the time. When in the clear, a PL tone of 167.9 is commonly used.
Frequency ranges commonly used nationwide are: 162.6125 - 162.7875 163.8375 - 163.9755 167.2125 - 167.7875 173.025 - 173.175
167.5625 simplex is the nationwide FBI Common channel.