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TABLE 5–1
AM BROADCAST STATION TECHNICAL STANDARDS
AM, FM, and Digital Modulated Systems Chap. 5
Item
Assigned frequency, f c
Channel bandwidth
Carrier frequency stability
Clear-channel frequencies
(One Class A, 50-kW station)
(Nondirectional)
Clear-channel frequencies
(Multiple 50-kW stations)
(Directional night)
Clear-channel frequencies
(For Bahama, Cuba, Canada,
or Mexico)
Local channel frequencies
(1-kW stations)
Maximum power licensed
Travelers’ Information Radio
(50 W maximum, usually 10 W)
FCC Technical Standard
In 10-kHz increments from 540 to 1,700 kHz
10 kHz
;20 Hz of the assigned frequency
640, 650, 660, 670, 700, 720, 750, 760, 770, 780, 820,
830, 840, 870, 880, 890, 1,020, 1,030, 1,040, 1,070,
1,100, 1,120, 1,160, 1,180, 1,200, and 1,210 kHz
680, 710, 810, 850, 1,000, 1,060, 1,080, 1,090, 1,110,
1,130, 1,140, 1,170, 1,190, 1,500, 1,510, 1,520, and
1,530 kHz
540, 690, 730, 740, 800, 860, 900, 940, 990, 1,010, 1,050,
1,220, 1,540, 1,550, 1,560, 1,570, and 1,580 kHz
1,230, 1,240, 1,340, 1,400, 1,450, and 1,490 kHz
50 kW
In 10 kHz increments from 530 to 1,700 kHz
clear-channel frequencies when they can be implemented without interfering with the
dominant clear-channel station. Often, to prevent interference, these secondary stations have
to operate with directional antenna patterns such that there is a null in the direction of the
dominant station. This is especially true for nighttime operation, when sky-wave propagation
allows a clear-channel station to cover half of the United States.
Class B stations operate full time to cover a regional area. Most Class B stations have a
power of 5 kW, although some operate with power as large as 50 kW. Class C stations cover a
local area full time, and most operate with a power of 1 kW. Hundreds of Class C stations are
assigned to each local-channel frequency (see Table 5–1), so the nighttime sky-wave interference
is large on these frequencies. Because of this interference, the night time coverage radius
of a Class C station may be as small as 5 miles from the transmitter site. Class D stations operate
daytime, some with powers as large as 50 kW, and, if allowed to operate at night, with
nighttime power of 250 watts or less. For a listing of AM broadcasting stations in the United
States go to www.fcc.govmbaudioamg.html.
International broadcast AM stations, which operate in the shortwave bands (3 to 30
MHz), generally do so with high power levels. Some of these feed 500 kW of carrier power
into directional antennas that produce effective radiated power levels in the megawatt range
(i.e., when the gain of the directional antenna is included).
Digital AM Broadcasting
In the United States, the FCC has adopted the iBiquity in band on channel (IBOC) system for
digital broadcasting in the AM band (i.e., medium wave, 540 to 1,700 kHz). This IBOC system
provides for simultaneous transmission of digital audio data and auxiliary digital data along
with a conventional AM signal (modulated by analog audio). Consequently, a conventional