In a conventional radio system, a radio can access only one channel at a time. If that channel is in use, the user must either wait for
the channel to become idle or manually search for a free channel. The radio service code for conventional systems is IG (Business).
A trunked radio system differs from a conventional system in its ability to automatically search two or more
available channels and assign a user an open channel. See 47 CFR 90.7
Trunked radio systems operating on PLMR channels between 150-512 MHz must employ equipment that prevents
transmission on a trunked frequency if a signal from another system is present on that frequency.
The level of monitoring must be sufficient to avoid causing harmful interference to other systems. See 47 CFR 90.187(b).
Exception: A frequency in a trunked radio system is exempt from the monitoring requirements if (1) in the 470-512 MHz band,
the licensee meets the loading requirements of 47 CFR 90.313 and has exclusivity in its service area; or
(2) the licensee has obtained consent from all
"affected licensees" using either the "mileage separation" or "protected contours" procedures under 47 CFR 90.187(b)(2).
On December 7, 2001, the Wireless Telecommunications Bureau (Bureau) accepted and approved consensus monitoring levels for non-exempt
trunked systems operating on Private Land Mobile Radio (PLMR) channels between 150-512 MHz. These monitoring levels were recommended
by the Commission's certified Frequency Advisory Committees ("FACs" or "coordinators") for PLMR spectrum.
For more information see Public Notice DA 01-2852 (Word