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

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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 than 141 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]