Goto Section: 73.1 | 73.21 | Table of Contents
Revised as of November 30, 2020
Goto Year:2020 |
§ 73.14 AM broadcast definitions.
AM broadcast band. The band of frequencies extending from 535 to 1705
AM broadcast channel. The band of frequencies occupied by the carrier
and the upper and lower sidebands of an AM broadcast signal with the
carrier frequency at the center. Channels are designated by their
assigned carrier frequencies. The 117 carrier frequencies assigned to
AM broadcast stations begin at 540 kHz and progress in 10 kHz steps to
1700 kHz. (See § 73.21 for the classification of AM broadcast channels).
AM broadcast station. A broadcast station licensed for the
dissemination of radio communications intended to be received by the
public and operated on a channel in the AM broadcast band.
Amplitude modulated stage. The radio-frequency stage to which the
modulator is coupled and in which the carrier wave is modulated in
accordance with the system of amplitude modulation and the
characteristics of the modulating wave.
Amplitude modulator stage. The last amplifier stage of the modulating
wave amplitude modulates a radio-frequency stage.
Antenna current. The radio-frequency current in the antenna with no
Antenna input power. The product of the square of the antenna current
and the antenna resistance at the point where the current is measured.
Antenna resistance. The total resistance of the transmitting antenna
system at the operating frequency and at the point at which the antenna
current is measured.
Auxiliary facility. An auxiliary facility is an AM antenna tower(s)
separate from the main facility's antenna tower(s), permanently
installed at the same site or at a different location, from which an AM
station may broadcast for short periods without prior Commission
authorization or notice to the Commission while the main facility is
not in operation (e.g., where tower work necessitates turning off the
main antenna or where lightning has caused damage to the main antenna
or transmission system) (See § 73.1675).
Blanketing. The interference which is caused by the presence of an AM
broadcast signal of one volt per meter (V/m) or greater strengths in
the area adjacent to the antenna of the transmitting station. The 1 V/m
contour is referred to as the blanket contour and the area within this
contour is referred to as the blanket area.
Carrier-amplitude regulation (Carrier shift). The change in amplitude
of the carrier wave in an amplitude-modulated transmitter when
modulation is applied under conditions of symmetrical modulation.
Combined audio harmonics. The arithmetical sum of the amplitudes of all
the separate harmonic components. Root sum square harmonic readings may
be accepted under conditions prescribed by the FCC.
Critical hours. The two hour period immediately following local sunrise
and the two hour period immediately preceding local sunset.
Daytime. The period of time between local sunrise and local sunset.
Effective field; Effective field strength. The root-mean-square (RMS)
value of the inverse distance fields at a distance of 1 kilometer from
the antenna in all directions in the horizontal plane. The term “field
strength” is synonymous with the term “field intensity” as contained
elsewhere in this Part.
Equipment performance measurements. The measurements performed to
determine the overall performance characteristics of a broadcast
transmission system from point of program origination to sampling of
signal as radiated. (See § 73.1590)
Experimental period. the time between 12 midnight local time and local
sunrise, used by AM stations for tests, maintenance and
Frequency departure. The amount of variation of a carrier frequency or
center frequency from its assigned value.
Incidental phase modulation. The peak phase deviation (in radians)
resulting from the process of amplitude modulation.
Input power. Means the product of the direct voltage applied to the
last radio stage and the total direct current flowing to the last radio
stage, measured without modulation.
Intermittent service area. Means the area receiving service from the
groundwave of a broadcast station but beyond the primary service area
and subject to some interference and fading.
Last radio stage. The radio-frequency power amplifier stage which
supplies power to the antenna.
Left (or right) signal. The electrical output of a microphone or
combination of microphones placed so as to convey the intensity, time,
and location of sounds originated predominately to the listener's left
(or right) of the center of the performing area.
Left (or right) stereophonic channel. The left (or right) signal as
electrically reproduced in reception of AM stereophonic broadcasts.
Main channel. The band of audio frequencies from 50 to 10,000 Hz which
amplitude modulates the carrier.
Maximum percentage of modulation. The greatest percentage of modulation
that may be obtained by a transmitter without producing in its output,
harmonics of the modulating frequency in excess of those permitted by
these regulations. (See § 73.1570)
Maximum rated carrier power. The maximum power at which the transmitter
can be operated satisfactorily and is determined by the design of the
transmitter and the type and number of vacuum tubes or other amplifier
devices used in the last radio stage.
Model I facility. A station operating in the 1605-1705 kHz band
featuring fulltime operation with stereo, competitive technical
quality, 10 kW daytime power, 1 kW nighttime power, non-directional
antenna (or a simple directional antenna system), and separated by
400-800 km from other co-channel stations.
Model II facility. A station operating in the 535-1605 kHz band
featuring fulltime operation, competitive technical quality, wide area
daytime coverage with nighttime coverage at least 15% of the daytime
Modulation dependent carrier level (MDCL) control technologies.
Transmitter control techniques that vary either the carrier power level
or both the carrier and sideband power levels as a function of the
Nighttime. The period of time between local sunset and local sunrise.
Nominal power. The antenna input power less any power loss through a
dissipative network and, for directional antennas, without
consideration of adjustments specified in paragraphs (b)(1) and (b)(2)
of § 73.51 of the rules. However, for AM broadcast applications granted
or filed before June 3, 1985, nominal power is specified in a system of
classifications which include the following values: 50 kW, 25 kW, 10
kW, 5 kW, 2.5 kW, 1 kW, 0.5 kW, and 0.25 kW. The specified nominal
power for any station in this group of stations will be retained until
action is taken on or after June 3, 1985, which involves a change in
the technical facilities of the station.
Percentage modulation (amplitude)
In a positive direction:
M = MAX−C × 100
In a negative direction:
M = C−MIN × 100
M = Modulation level in percent.
MAX = Instantaneous maximum level of the modulated radio frequency
MIN = Instantaneous minimum level of the modulated radio frequency
C = (Carrier) level of radio frequency envelope without modulation.
Plate modulation. The modulation produced by introduction of the
modulating wave into the plate circuit of any tube in which the carrier
frequency wave is present.
Primary service area. Means the service area of a broadcast station in
which the groundwave is not subject to objectionable interference or
Proof of performance measurements or antenna proof of performance
measurements. The measurements of field strengths made to determine the
radiation pattern or characteristics of an AM directional antenna
Secondary service area. Means the service area of a broadcast station
served by the skywave and not subject to objectionable interference and
in which the signal is subject to intermittent variations in strength.
Stereophonic channel. The band of audio frequencies from 50 to 10,000
Hz containing the stereophonic information which modulates the radio
Stereophonic crosstalk. An undesired signal occurring in the main
channel from modulation of the stereophonic channel or that occurring
in the stereophonic channel from modulation of the main channel.
Stereophonic pilot tone. An audio tone of fixed or variable frequency
modulating the carrier during the transmission of stereophonic
Stereophonic separation. The ratio of the electrical signal caused in
the right (or left) stereophonic channel to the electrical signal
caused in the left (or right) stereophonic channel by the transmission
of only a right (or left) signal.
Sunrise and sunset. For each particular location and during any
particular month, the time of sunrise and sunset as specified in the
instrument of authorization (See § 73.1209).
White area. The area or population which does not receive
interference-free primary service from an authorized AM station or does
not receive a signal strength of at least 1 mV/m from an authorized FM
[ 47 FR 8587 , Mar. 1, 1982, as amended at 47 FR 13164 , Mar. 29, 1982; 47 FR 13812 , Apr. 1, 1982; 50 FR 18821 , May 2, 1985; 50 FR 47054 , Nov. 14,
1985; 56 FR 64856 , Dec. 12, 1991; 62 FR 51058 , Sept. 30, 1997; 66 FR 20755 , Apr. 25, 2001; 81 FR 2759 , Jan. 19, 2016; 82 FR 57882 , Dec. 8,
Goto Section: 73.1 | 73.21
Goto Year: 2020 |
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