AMPLITUDE MODULATION (AM) Radio is the oldest form of broadcasting, officially started by Pittsburgh station KDKA on November 2, 1920, when it broadcast that year's Presidential election returns.
AM stations in North America operate on frequencies of 535 to 1705 kilohertz (kHz) by authority of the Federal Communications Commission (FCC).
The classes of AM stations in the U.S. are as follows:
CLEAR--stations designed to serve wide areas; protected from objectionable interference from smaller stations within their primary service areas, and where appicable, secondary service areas.
Stations operating on these channels are classified as follows:
1) Class A--unlimited time (24 hour) stations designed to render service to both primary and secondary service areas over extended distances from their transmitters, because their primary areas are protected from interference on the same and adjacent channels and secondary areas are protected by interference by stations on the same channel; powers between 10 and 50 kilowatts (kW)=10,000-50,000 watts
2) Class B--unlimited timers designed to render service only in primary service areas; powers between .25 and 50 kW (10 kw on 1605-1705 kHz)
3) Class D--stations operating during the daytime (sunrise to sunset), limited time (specified hours) or unlimited time with daytime powers between .25 and 50 kW and nighttime powers less than .25
kW
The clear channel frequencies are as follows:
a) One class A station allowed: 640-670, 700, 720, 750-780, 820-840, 870-890, 1020-1040, 1100, 1120, 1160, 1180, 1210, and 1210 kHz (mainland U.S. stations only)
b) classes A, B, and D: 540, 680-690, 710, 730-740, 800-810, 850-860, 900, 990-1010, 1050-1090, 1110, 1130-1140, 1170, 1190, 1220, and 1500-1580 kHz.
REGIONAL--stations designed to serve a primary center of population and the adjacent areas; used by class B and class D stations on these frequencies: 550-630, 790, 910-930, 950-980, 1150, 1250-1330, 1350-1390, 1410-1440, 1460-1480, and 1590-1700 kHz.
LOCAL (Class D)--stations designed to serve primarily a community and small adjacent areas; powers between .25 and 1 kW only; used on these frequencies: 1230, 1240, 1340, 1400, 1450, and 1490 kHz.
now... the 50 kW AM Radio Superstations!!!