Sec.  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 45 ° 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  Sec. 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 of radiation.

   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  Sec. 73.1675).

   Center frequency. The term “center frequency” means:

   (1) The average frequency of the emitted wave when modulated by a sinusoidal
   signal.

   (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) relative field.

   Composite baseband signal. A signal which is composed of all program and
   other communications signals that frequency modulates the FM carrier.

   Effective radiated power. The term “effective radiated power” 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 “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.

   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 broadcasting.

   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 107.9 MHz.

   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 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 modulated wave and the
   carrier frequency.

   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 during modulation.

   Multiplex transmission. The term “multiplex transmission” 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  �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 channel.

   FM stereophonic broadcast. The transmission of a stereophonic program by a
   single FM broadcast station utilizing the main channel and a stereophonic
   subchannel.

   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]