§ 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 § 73.182).
   The operating power shall not be less than 10 kW nor more than 50 kW.
   (Also see § 73.25(a)).

   (2) Class B station. 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 107.5 mV/m at 1 kilometer) 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 than 107.5 mV/m at 1 kilometer.
   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 § 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, as amended at  81 FR 2759 , Jan. 19, 2016]

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