#### § 73.681 Definitions.

*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. 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.

*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* § 73.1675).

*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.

*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.

*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.

*Polarization.* The direction of the electric field as radiated from the transmitting antenna.

*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 608 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 608 megahertz (channels 14 through 36).

*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.

[89 FR 7252, Feb. 1, 2024]