§ 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 § 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
   § 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]

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