Goto Section: 73.297 | 73.311 | Table of Contents
Revised as of November 25, 2020
Goto Year:2020 |
§ 73.310 FM technical definitions.
(a) Frequency modulation. Antenna height above average terrain (HAAT).
HAAT is calculated by: determining the average of the antenna heights
above the terrain from 3 to 16 kilometers (2 to 10 miles) from the
antenna for the eight directions evenly spaced for each 45Â° of azimuth
starting with True North (a different antenna height will be determined
in each direction from the antenna): and computing the average of these
separate heights. In some cases less than eight directions may be used.
(See § 73.313(d).) Where circular or elliptical polarization is used,
the antenna height above average terrain must be based upon the height
of the radiation of the antenna that transmits the horizontal component
Antenna power gain. The square of the ratio of the root-mean-square
(RMS) free space field strength produced at 1 kilometer in the
horizontal plane in millivolts per meter for 1 kW antenna input power
to 221.4 mV/m. This ratio is expressed in decibels (dB). If specified
for a particular direction, antenna power gain is based on that field
strength in the direction only.
Auxiliary facility. An auxiliary facility is an antenna separate from
the main facility's antenna, permanently installed on the same tower or
at a different location, from which a 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
Center frequency. The term âcenter frequencyâ means:
(1) The average frequency of the emitted wave when modulated by a
(2) The frequency of the emitted wave without modulation.
Composite antenna pattern. The composite antenna pattern is a relative
field horizontal plane pattern for 360 degrees of azimuth, for which
the value at a particular azimuth is the greater of the horizontally
polarized or vertically polarized component relative field values. The
composite antenna pattern is normalized to a maximum of unity (1.000)
Composite baseband signal. A signal which is composed of all program
and other communications signals that frequency modulates the FM
Effective radiated power. The term âeffective radiated powerâ means the
product of the antenna power (transmitter output power less
transmission line loss) times: (1) The antenna power gain, or (2) the
antenna field gain squared. Where circular or elliptical polarization
is employed, the term effective radiated power is applied separately to
the horizontal and vertical components of radiation. For allocation
purposes, the effective radiated power authorized is the horizontally
polarized component of radiation only.
Equivalent isotropically radiated power (EIRP). The term âequivalent
isotropically radiated power (also known as âeffective radiated power
above isotropic) means the product of the antenna input power and the
antenna gain in a given direction relative to an isotropic antenna.
FM Blanketing. Blanketing is that form of interference to the reception
of other broadcast stations which is caused by the presence of an FM
broadcast signal of 115 dBu (562 mV/m) or greater signal strength in
the area adjacent to the antenna of the transmitting station. The 115
dBu contour is referred to as the blanketing contour and the area
within this contour is referred to as the blanketing area.
FM broadcast band. The band of frequencies extending from 88 to 108
MHz, which includes those assigned to noncommercial educational
FM broadcast channel. A band of frequencies 200 kHz wide and designated
by its center frequency. Channels for FM broadcast stations begin at
88.1 MHz and continue in successive steps of 200 kHz to and including
FM broadcast station. A station employing frequency modulation in the
FM broadcast band and licensed primarily for the transmission of
radiotelephone emissions intended to be received by the general public.
Field strength. The electric field strength in the horizontal plane.
Free space field strength. The field strength that would exist at a
point in the absence of waves reflected from the earth or other
Frequency departure. The amount of variation of a carrier frequency or
center frequency from its assigned value.
Frequency deviation. The peak difference between modulated wave and the
Frequency modulation. A system of modulation where the instantaneous
radio frequency varies in proportion to the instantaneous amplitude of
the modulating signal (amplitude of modulating signal to be measured
after pre-emphasis, if used) and the instantaneous radio frequency is
independent of the frequency of the modulating signal.
Frequency swing. The peak difference between the maximum and the
minimum values of the instantaneous frequency of the carrier wave
Multiplex transmission. The term âmultiplex transmissionâ means the
simultaneous transmission of two or more signals within a single
channel. Multiplex transmission as applied to FM broadcast stations
means the transmission of facsimile or other signals in addition to the
regular broadcast signals.
Percentage modulation. The ratio of the actual frequency deviation to
the frequency deviation defined as 100% modulation, expressed in
percentage. For FM broadcast stations, a frequency deviation of Â±75kHz
is defined as 100% modulation.
(b) Stereophonic sound broadcasting. Cross-talk. An undesired signal
occurring in one channel caused by an electrical signal in another
FM stereophonic broadcast. The transmission of a stereophonic program
by a single FM broadcast station utilizing the main channel and a
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 originating 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 FM stereophonic broadcasts.
Main channel. The band of frequencies from 50 to 15,000 Hz which
frequency-modulate the main carrier.
Pilot subcarrier. A subcarrier that serves as a control signal for use
in the reception of FM stereophonic sound broadcasts.
Stereophonic separation. The ratio of the electrical signal caused in
sound channel A to the signal caused in sound channel B by the
transmission of only a channel B signal. Channels A and B may be any
two channels of a stereophonic sound broadcast transmission system.
Stereophonic sound. The audio information carried by plurality of
channels arranged to afford the listener a sense of the spatial
distribution of sound sources. Stereophonic sound broadcasting
includes, but is not limited to, biphonic (two channel), triphonic
(three channel) and quadrophonic (four channel) program services.
Stereophonic sound subcarrier. A subcarrier within the FM broadcast
baseband used for transmitting signals for stereophonic sound reception
of the main broadcast program service.
Stereophonic sound subchannel. The band of frequencies from 23 kHz to
99 kHz containing sound subcarriers and their associated sidebands.
(c) Visual transmissions. Communications or message transmitted on a
subcarrier intended for reception and visual presentation on a viewing
screen, teleprinter, facsimile printer, or other form of graphic
display or record.
(d) Control and telemetry transmissions. Signals transmitted on a
multiplex subcarrier intended for any form of control and switching
functions or for equipment status data and aural or visual alarms.
[ 28 FR 13623 , Dec. 14, 1963, as amended at 39 FR 10575 , Mar. 21, 1974;
44 FR 36038 , June 20, 1979; 48 FR 28454 , June 22, 1983; 48 FR 29507 ,
June 27, 1983; 48 FR 37216 , Aug. 17, 1983; 49 FR 45145 , Nov. 15, 1984;
57 FR 48333 , Oct. 23, 1992; 62 FR 51058 , Sept. 30, 1997]
Goto Section: 73.297 | 73.311
Goto Year: 2020 |
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