47 CFR Ch. I (10–1–18 Edition) § 73.310

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§ 73.310 47 CFR Ch. I (10–1–18 Edition)

§ 73.310 FM technical definitions. field values. The composite antenna (a) Frequency modulation. Antenna pattern is normalized to a maximum of height above average terrain (HAAT). unity (1.000) relative field. HAAT is calculated by: determining Composite baseband signal. A signal the average of the antenna heights which is composed of all program and above the terrain from 3 to 16 kilo- other communications signals that fre- meters (2 to 10 miles) from the antenna quency modulates the FM carrier. for the eight directions evenly spaced Effective radiated power. The term for each 45° of azimuth starting with ‘‘effective radiated power’’ means the True North (a different antenna height product of the antenna power (trans- will be determined in each direction mitter output power less transmission from the antenna): and computing the line loss) times: (1) The antenna power average of these separate heights. In gain, or (2) the antenna field gain some cases less than eight directions squared. Where circular or elliptical may be used. (See § 73.313(d).) Where polarization is employed, the term ef- circular or elliptical polarization is fective radiated power is applied sepa- used, the antenna height above average rately to the horizontal and vertical terrain must be based upon the height components of radiation. For alloca- of the radiation of the antenna that tion purposes, the effective radiated transmits the horizontal component of power authorized is the horizontally radiation. polarized component of radiation only. Antenna power gain. The square of the Equivalent isotropically radiated power ratio of the root-mean-square (RMS) (EIRP). The term ‘‘equivalent free space field strength produced at 1 isotropically radiated power (also kilometer in the horizontal plane in known as ‘‘effective radiated power millivolts per meter for 1 kW antenna above isotropic) means the product of input power to 221.4 mV/m. This ratio the antenna input power and the an- is expressed in decibels (dB). If speci- tenna gain in a given direction relative fied for a particular direction, antenna to an isotropic antenna. power gain is based on that field FM Blanketing. Blanketing is that strength in the direction only. form of interference to the reception of Auxiliary facility. An auxiliary facility is an antenna separate from the other broadcast stations which is main facility’s antenna, permanently caused by the presence of an FM broad- installed on the same tower or at a dif- cast signal of 115 dBu (562 mV/m) or ferent location, from which a station greater signal strength in the area ad- may broadcast for short periods with- jacent to the antenna of the transmit- out prior Commission authorization or ting station. The 115 dBu contour is re- notice to the Commission while the ferred to as the blanketing contour and main facility is not in operation (e.g., the area within this contour is referred where tower work necessitates turning to as the blanketing area. off the main antenna or where light- FM broadcast band. The band of fre- ning has caused damage to the main quencies extending from 88 to 108 MHz, antenna or transmission system) (See which includes those assigned to non- § 73.1675). commercial educational broadcasting. Center frequency. The term ‘‘center FM broadcast channel. A band of fre- frequency’’ means: quencies 200 kHz wide and designated (1) The average frequency of the by its center frequency. Channels for emitted wave when modulated by a si- FM broadcast stations begin at 88.1 nusoidal signal. MHz and continue in successive steps (2) The frequency of the emitted wave of 200 kHz to and including 107.9 MHz. without modulation. FM broadcast station. A station em- Composite antenna pattern. The com- ploying frequency modulation in the posite antenna pattern is a relative FM broadcast band and licensed pri- field horizontal plane pattern for 360 marily for the transmission of radio- degrees of azimuth, for which the value telephone emissions intended to be re- at a particular azimuth is the greater ceived by the general public. of the horizontally polarized or Field strength. The electric field vertically polarized component relative strength in the horizontal plane.

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Free space field strength. The field reproduced in reception of FM stereo- strength that would exist at a point in phonic broadcasts. the absence of waves reflected from the Main channel. The band of fre- earth or other reflecting objects. quencies from 50 to 15,000 Hz which fre- Frequency departure. The amount of quency-modulate the main carrier. variation of a carrier frequency or cen- Pilot subcarrier. A subcarrier that ter frequency from its assigned value. serves as a control signal for use in the Frequency deviation. The peak dif- reception of FM stereophonic sound ference between modulated wave and broadcasts. the carrier frequency. Stereophonic separation. The ratio of Frequency modulation. A system of the electrical signal caused in sound modulation where the instantaneous channel A to the signal caused in sound radio frequency varies in proportion to channel B by the transmission of only the instantaneous amplitude of the a channel B signal. Channels A and B modulating signal (amplitude of modu- may be any two channels of a stereo- lating signal to be measured after pre- phonic sound broadcast transmission emphasis, if used) and the instanta- system. neous radio frequency is independent of Stereophonic sound. The audio infor- the frequency of the modulating signal. mation carried by plurality of channels Frequency swing. The peak difference arranged to afford the listener a sense between the maximum and the min- of the spatial distribution of sound imum values of the instantaneous fre- sources. Stereophonic sound broad- quency of the carrier wave during mod- casting includes, but is not limited to, ulation. biphonic (two channel), triphonic Multiplex transmission. The term (three channel) and quadrophonic (four ‘‘multiplex transmission’’ means the channel) program services. simultaneous transmission of two or Stereophonic sound subcarrier. A sub- more signals within a single channel. carrier within the FM broadcast Multiplex transmission as applied to baseband used for transmitting signals FM broadcast stations means the for stereophonic sound reception of the transmission of facsimile or other sig- main broadcast program service. nals in addition to the regular broad- Stereophonic sound subchannel. The cast signals. band of frequencies from 23 kHz to 99 Percentage modulation. The ratio of kHz containing sound subcarriers and the actual frequency deviation to the their associated sidebands. frequency deviation defined as 100% (c) Visual transmissions. Communica- modulation, expressed in percentage. tions or message transmitted on a sub- For FM broadcast stations, a frequency carrier intended for reception and vis- deviation of ±75kHz is defined as 100% ual presentation on a viewing screen, modulation. teleprinter, facsimile printer, or other (b) Stereophonic sound broadcasting. form of graphic display or record. Cross-talk. An undesired signal occur- (d) Control and telemetry transmissions. ring in one channel caused by an elec- Signals transmitted on a multiplex trical signal in another channel. subcarrier intended for any form of FM stereophonic broadcast. The trans- control and switching functions or for mission of a stereophonic program by a equipment status data and aural or vis- single FM broadcast station utilizing ual alarms. the main channel and a stereophonic [28 FR 13623, Dec. 14, 1963, as amended at 39 subchannel. FR 10575, Mar. 21, 1974; 44 FR 36038, June 20, Left (or right) signal. The electrical 1979; 48 FR 28454, June 22, 1983; 48 FR 29507, output of a microphone or combination June 27, 1983; 48 FR 37216, Aug. 17, 1983; 49 FR of microphones placed so as to convey 45145, Nov. 15, 1984; 57 FR 48333, Oct. 23, 1992; the intensity, time, and location of 62 FR 51058, Sept. 30, 1997] sounds originating predominately to the listener’s left (or right) of the cen- § 73.311 Field strength contours. ter of the performing area. (a) Applications for FM broadcast au- Left (or right) stereophonic channel. thorizations must show the field The left (or right) signal as electrically strength contours required by FCC

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