Sec.  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
    Sec. 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 transmitted.

   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  Sec. 73.1675).

   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 specific
   chromaticity.

   Chrominance subcarrier. The carrier which is modulated by the chrominance
   information.

   Color transmission. The transmission of color television signals which can
   be reproduced with different values of hue, saturation, and luminance.

   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 be considered.

   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 reflecting objects.

   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 during modulation.

   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 frequency.

   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  Sec. 73.682, the relationship of the IRE standard scale to the
   conventional measure of modulation is as follows:


------------------------------------------------------------------------
                                                      IRE
                                                   standard   Modulation
                      Level                          scale    percentage
                                                    (units)
------------------------------------------------------------------------
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 audio information.

   Multiplex Transmission (Aural). A subchannel added to the regular aural
   carrier of a television broadcast station by means of frequency modulated
   subcarriers.

   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 100%
   modulation.

   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
   transmitting antenna.

   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
   direction.

   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
   transmission standards.

   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 69).

   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 broadcast
   station.

   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, as amended at  35 FR 5692 , Apr. 8, 1970;  36 FR 5505 , Mar. 24, 1971;  36 FR 17429 , Aug. 31, 1971;  41 FR 56325 , Dec. 28, 1976;
    42 FR 20823 , Apr. 22, 1977;  44 FR 36039 , June 20, 1979;  47 FR 35990 , Aug.
   18, 1982;  49 FR 18106 , Apr. 27, 1984;  49 FR 38131 , Sept. 27, 1984;  49 FR 50048 , Dec. 26, 1984;  50 FR 23699 , June 5, 1985;  51 FR 12616 , Apr. 14, 1986;
    56 FR 49707 , Oct. 1, 1991;  58 FR 44951 , Aug. 25, 1993;  62 FR 51059 , Sept.
   30, 1997]