The AM frequency of 1140 kilohertz is defined by the FCC as a Clear Channel frequency.
Class A, B, and D stations can be assigned to 1140, as long as protection is provided to the Class A stations.
In Idaho, KGEM is the only station on 1140. Across the US, however, there are over 30 stations assigned to this frequency, several in Canada, and several in Mexico and other North American areas. It is for this reason stations on this frequency either reduce power or switch to a directional antenna (or both) at night to reduce interference.
Some stations on 1140 operate only during daytime hours. (Information updated March 2014)