800 kHz 

The AM frequency of 670 kilohertz is defined by the FCC as a Clear Channel Class A frequency.  However, some class B and D stations are assigned clear channel frequencies, as long as protection is provided to the Class A station.  In Idaho, KBRV is the only station on 800, and is a class D station.  Across the US, however, there are 30  stations assigned to this frequency, several in Canada, 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.     (Information updated March 2014)