FCC 73.681 Revised as of December 4, 2012
Goto Year:2011 |
§ 73.681 Definitions.
Amplitude modulation ( AM ). A system of modulation in which the
envelope of the transmitted wave contains a component similar to the
wave form of the signal to be transmitted.
Antenna electrical beam tilt. The shaping of the radiation pattern in
the vertical plane of a transmitting antenna by electrical means so
that maximum radiation occurs at an angle below the horizontal plane.
Antenna height above average terrain. The average of the antenna
heights above the terrain from approximately 3.2 (2 miles) to 16.1
kilometers (10 miles) from the antenna for the eight directions spaced
evenly for each 45 degrees of azimuth starting with True North. (In
general, a different antenna height will be determined in each
direction from the antenna. The average of these various heights is
considered the antenna height above the average terrain. In some cases
less than 8 directions may be used. See § 73.684(d)). Where circular or
elliptical polarization is employed, the antenna height above average
terrain shall be based upon the height of the radiation center of the
antenna which transmits the horizontal component of radiation.
Antenna mechanical beam tilt. The intentional installation of a
transmitting antenna so that its axis is not vertical, in order to
change the normal angle of maximum radiation in the vertical plane.
Antenna power gain. The square of the ratio of the root-mean-square
free space field strength produced at 1 kilometer in the horizontal
plane, in millivolts per meter for one kW antenna input power to 221.4
mV/m. This ratio should be expressed in decibels (dB). (If specified
for a particular direction, antenna power gain is based on the field
strength in that direction only.)
Aspect ratio. The ratio of picture width to picture height as
Aural center frequency. (1) The average frequency of the emitted wave
when modulated by a sinusoidal signal; (2) the frequency of the emitted
wave without modulation.
Aural transmitter. The radio equipment for the transmission of the
aural signal only.
Auxiliary facility. An auxiliary facility is an antenna separate a 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
BTSC. Broadcast Television systems committee recommendation for
multichannel television sound transmission and audio processing as
defined in FCC Bulletin OET 60.
Baseband. Aural transmitter input signals between 0 and 120 kHz.
Blanking level. The level of the signal during the blanking interval,
except the interval during the scanning synchronizing pulse and the
chrominance subcarrier synchronizing burst.
Chrominance. The colorimetric difference between any color and a
reference color of equal luminance, the reference color having a
Chrominance subcarrier. The carrier which is modulated by the
Color transmission. The transmission of color television signals which
can be reproduced with different values of hue, saturation, and
Effective radiated power. The product of the antenna input power and
the antenna power gain. This product should be expressed in kW and in
dB above 1 kW (dBk). (If specified for a particular direction,
effective radiated power is based on the antenna power gain in that
direction only. The licensed effective radiated power is based on the
maximum antenna power gain. When a station is authorized to use a
directional antenna or an antenna beam tilt, the direction of the
maximum effective radiated power will be specified.) Where circular or
elliptical polarization is employed, the term effective radiated power
is applied separately to the horizontally and vertically polarized
components of radiation. For assignment purposes, only the effective
radiated power authorized for the horizontally polarized component will
Equivalent isotropically radiated power (EIRP). The term “equivalent
isotropically radiated power” (also known as “effective 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.
Field. Scanning through the picture area once in the chosen scanning
pattern. In the line interlaced scanning pattern of two to one, the
scanning of the alternate lines of the picture area once.
Frame. Scanning all of the picture area once. In the line interlaced
scanning pattern of two to one, a frame consists of two fields.
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 the instantaneous
frequency of the modulated wave and the carrier frequency.
Frequency modulation ( FM ). 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
Interlaced scanning. A scanning process in which successively scanned
lines are spaced an integral number of line widths, and in which the
adjacent lines are scanned during successive cycles of the field
IRE standard scale. A linear scale for measuring, in IRE units, the
relative amplitudes of the components of a television signal from a
zero reference at blanking level, with picture information falling in
the positive, and synchronizing information in the negative domain.
Note: When a carrier is amplitude modulated by a television signal in
accordance with § 73.682, the relationship of the IRE standard scale to
the conventional measure of modulation is as follows:
Level IRE standard scale (units) Modulation percentage
Zero carrier 120 0
Reference white 100 12.5
Blanking 0 75
Synchronizing peaks (maximum carrier level) −40 100
Luminance. Luminous flux emitted, reflected, or transmitted per unit
solid angle per unit projected area of the source.
Main channel. The band of frequencies from 50 to 15,000 Hertz which
frequency modulate the main aural carrier.
Monochrome transmission. The transmission of television signals which
can be reproduced in gradations of a single color only.
Multichannel Television Sound (MTS). Any system of aural transmission
that utilizes aural baseband operation between 15 kHz and 120 kHz to
convey information or that encodes digital information in the video
portion of the television signal that is intended to be decoded as
Multiplex Transmission ( Aural ). A subchannel added to the regular
aural carrier of a television broadcast station by means of frequency
Negative transmission. Where a decrease in initial light intensity
causes an increase in the transmitted power.
Peak power. The power over a radio frequency cycle corresponding in
amplitude to synchronizing peaks.
Percentage modulation. As applied to frequency modulation, the ratio of
the actual frequency deviation to the frequency deviation defined as
100% modulation expressed in percentage. For the aural transmitter of
TV broadcast stations, a frequency deviation of ±25 kHz is defined as
Pilot subcarrier. A subcarrier used in the reception of TV stereophonic
aural or other subchannel broadcasts.
Polarization. The direction of the electric field as radiated from the
Program related data signal. A signal, consisting of a series of pulses
representing data, which is transmitted simultaneously with and
directly related to the accompanying television program.
Reference black level. The level corresponding to the specified maximum
excursion of the luminance signal in the black direction.
Reference white level of the luminance signal. The level corresponding
to the specified maximum excursion of the luminance signal in the white
Scanning. The process of analyzing successively, according to a
predetermined method, the light values of picture elements constituting
the total picture area.
Scanning line. A single continuous narrow strip of the picture area
containing highlights, shadows, and half-tones, determined by the
process of scanning.
Standard television signal. A signal which conforms to the television
Synchronization. The maintenance of one operation in step with another.
Television broadcast band. The frequencies in the band extending from
54 to 806 megahertz which are assignable to television broadcast
stations. These frequencies are 54 to 72 megahertz (channels 2 through
4), 76 to 88 megahertz (channels 5 and 6), 174 to 216 megahertz
(channels 7 through 13), and 470 to 806 megahertz (channels 14 through
Television broadcast station. A station in the television broadcast
band transmitting simultaneous visual and aural signals intended to be
received by the general public.
Television channel. A band of frequencies 6 MHz wide in the television
broadcast band and designated either by number or by the extreme lower
and upper frequencies.
Television transmission standards. The standards which determine the
characteristics of a television signal as radiated by a television
Television transmitter. The radio transmitter or transmitters for the
transmission of both visual and aural signals.
Vestigial sideband transmission. A system of transmission wherein one
of the generated sidebands is partially attenuated at the transmitter
and radiated only in part.
Visual carrier frequency. The frequency of the carrier which is
modulated by the picture information.
Visual transmitter. The radio equipment for the transmission of the
visual signal only.
Visual transmitter power. The peak power output when transmitting a
standard television signal.
[ 28 FR 13660 , Dec. 14, 1963]
Editorial Note: For Federal Register citations affecting § 73.681,
see the List of CFR Sections Affected, which appears in the Finding
Aids section of the printed volume and at www.fdsys.gov .
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