Sec.  73.21   Classes of AM broadcast channels and stations.

   (a) Clear channel. A clear channel is one on which stations are assigned to
   serve  wide  areas.  These  stations  are protected from objectionable
   interference within their primary service areas and, depending on the class
   of station, their secondary service areas. Stations operating on these
   channels are classified as follows:

   (1) Class A station. A Class A station is an unlimited time station that
   operates on a clear channel and is designed to render primary and secondary
   service over an extended area and at relatively long distances from its
   transmitter.  Its primary service area is protected from objectionable
   interference from other stations on the same and adjacent channels, and its
   secondary service area is protected from interference from other stations on
   the same channel. (See  Sec. 73.182). The operating power shall not be less than
   10 kW nor more than 50 kW. (Also see  Sec. 73.25(a)).

   (2) Class B station. A Class B station is an unlimited time station which is
   designed  to  render service only over a primary service area. Class B
   stations are authorized to operate with a minimum power of 0.25 kW (or, if
   less than 0.25 kW, an equivalent RMS antenna field of at least 141 mV/m at 1
   km) and a maximum power of 50 kW, or 10 kW for stations that are authorized
   to operate in the 1605–1705 kHz band.

   (3) Class D station. A Class D station operates either daytime, limited time
   or unlimited time with nighttime power less than 0.25 kW and an equivalent
   RMS antenna field of less than141 mV/m at one km. Class D stations shall
   operate with daytime powers not less than 0.25 kW nor more than 50 kW.
   Nighttime operations of Class D stations are not afforded protection and
   must protect all Class A and Class B operations during nighttime hours. New
   Class D stations that had not been previously licensed as Class B will not
   be authorized.

   (b) Regional Channel. A regional channel is one on which Class B and Class D
   stations may operate and serve primarily a principal center of population
   and the rural area contiguous thereto.

   Note: Until the North American Regional Broadcasting Agreement (NARBA) is
   terminated with respect to the Bahama Islands and the Dominican Republic,
   radiation toward those countries from a Class B station may not exceed the
   level  that  would  be  produced  by an omnidirectional antenna with a
   transmitted power of 5 kW, or such lower level as will comply with NARBA
   requirements  for protection of stations in the Bahama Islands and the
   Dominican Republic against objectionable interference.

   (c)  Local  channel.  A local channel is one on which stations operate
   unlimited time and serve primarily a community and the suburban and rural
   areas immediately contiguous thereto.

   (1) Class C station. A Class C station is a station operating on a local
   channel and is designed to render service only over a primary service area
   that may be reduced as a consequence of interference in accordance with
    Sec. 73.182. The power shall not be less than 0.25 kW, nor more than 1 kW. Class
   C stations that are licensed to operate with 0.1 kW may continue to do so.

   [ 56 FR 64856 , Dec. 12, 1991]