10 Subpart A—AM Broadcast Stations

§ 73.1 47 CFR Ch. I (10–1–18 Edition)

73.6007 Power limitations. Subpart A—AM Broadcast Stations 73.6008 Distance computations. 73.6010 Class A TV station protected con- § 73.1 Scope. tour. 73.6012 Protection of Class A TV, low power This subpart contains those rules TV, and TV translator stations. which apply exclusively to the AM 73.6013 Protection of DTV stations. broadcast service and are in addition to 73.6014 Protection of digital Class A TV sta- those rules in Subpart H which are tions. common to all AM, FM and TV broad- 73.6017 Digital Class A TV station protec- cast services, commercial and non- tion of Class A TV and digital Class A TV commercial. stations. [47 FR 8587, Mar. 1, 1982] 73.6018 Digital Class A TV station protection of DTV stations. § 73.14 AM broadcast definitions. 73.6019 Digital Class A TV station protection of low power TV, TV translator, dig- AM broadcast band. The band of fre- ital low power TV and digital TV trans- quencies extending from 535 to 1705 lator stations. kHz. 73.6020 Protection of stations in the land AM broadcast channel. The band of mobile radio service. frequencies occupied by the carrier and 73.6022 Negotiated interference and reloca- the upper and lower sidebands of an tion agreements. AM broadcast signal with the carrier 73.6023 Distributed transmission systems. frequency at the center. Channels are 73.6024 Transmission standards and system designated by their assigned carrier requirements. frequencies. The 117 carrier frequencies 73.6025 Antenna system and station loca- assigned to AM broadcast stations tion. begin at 540 kHz and progress in 10 kHz 73.6026 Broadcast regulations applicable to steps to 1700 kHz. (See § 73.21 for the Class A television stations. classification of AM broadcast chan- 73.6027 Class A TV notifications concerning interference to radio astronomy, re- nels). search and receiving installations. AM broadcast station. A broadcast sta- 73.6028 Class A television channel sharing tion licensed for the dissemination of outside the incentive auction. radio communications intended to be 73.6029 Class A television simulcasting dur- received by the public and operated on ing the ATSC 3.0 (Next Gen TV) transi- a channel in the AM broadcast band. tion. Amplitude modulated stage. The radio- frequency stage to which the modu- Subpart K—Application and Selection Pro- lator is coupled and in which the car- cedures for Reserved Noncommercial rier wave is modulated in accordance Educational Channels, and for Certain with the system of amplitude modula- Applications for Noncommercial Edu- tion and the characteristics of the cational Stations on Non-Reserved modulating wave. Channels Amplitude modulator stage. The last amplifier stage of the modulating wave 73.7000 Definition of terms (as used in subpart K only). amplitude modulates a radio-frequency 73.7001 Services subject to evaluation by stage. point system. Antenna current. The radio-frequency 73.7002 Fair distribution of service on re- current in the antenna with no modu- served band FM channels. lation. 73.7003 Point system selection procedures. Antenna input power. The product of 73.7004 Petitions to deny tentative se- the square of the antenna current and lectee(s). the antenna resistance at the point 73.7005 Holding period. where the current is measured. Antenna resistance. The total resist- Subpart L—Incorporated Standards ance of the transmitting antenna system at the operating frequency and at 73.8000 Incorporation by reference. the point at which the antenna current ALPHABETICAL INDEX—PART 73 is measured. AUTHORITY: 47 U.S.C. 154, 155, 301, 303, 307, Auxiliary facility. An auxiliary facil- 309, 310, 334, 336, 339. ity is an AM antenna tower(s) separate

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from the main facility’s antenna Frequency departure. The amount of tower(s), permanently installed at the variation of a carrier frequency or cen- same site or at a different location, ter frequency from its assigned value. from which an AM station may broad- Incidental phase modulation. The peak cast for short periods without prior phase deviation (in radians) resulting Commission authorization or notice to from the process of amplitude modula- the Commission while the main facil- tion. ity is not in operation (e.g., where Input power. Means the product of the tower work necessitates turning off the direct voltage applied to the last radio main antenna or where lightning has stage and the total direct current flow- caused damage to the main antenna or ing to the last radio stage, measured transmission system) (See § 73.1675). without modulation. Blanketing. The interference which is Intermittent service area. Means the caused by the presence of an AM broad- area receiving service from the cast signal of one volt per meter (V/m) groundwave of a broadcast station but or greater strengths in the area adja- beyond the primary service area and cent to the antenna of the transmit- subject to some interference and fad- ting station. The 1 V/m contour is re- ing. ferred to as the blanket contour and Last radio stage. The radio-frequency the area within this contour is referred power amplifier stage which supplies to as the blanket area. power to the antenna. Carrier-amplitude regulation (Carrier Left (or right) signal. The electrical shift). The change in amplitude of the output of a microphone or combination carrier wave in an amplitude-modu- of microphones placed so as to convey lated transmitter when modulation is the intensity, time, and location of applied under conditions of symmet- sounds originated predominately to the rical modulation. listener’s left (or right) of the center of Combined audio harmonics. The arith- the performing area. metical sum of the amplitudes of all Left (or right) stereophonic channel. the separate harmonic components. The left (or right) signal as electrically Root sum square harmonic readings reproduced in reception of AM stereo- may be accepted under conditions pre- phonic broadcasts. scribed by the FCC. Main channel. The band of audio fre- Critical hours. The two hour period quencies from 50 to 10,000 Hz which am- immediately following local sunrise plitude modulates the carrier. and the two hour period immediately Maximum percentage of modulation. preceding local sunset. The greatest percentage of modulation Daytime. The period of time between that may be obtained by a transmitter local sunrise and local sunset. without producing in its output, Effective field; Effective field strength. harmonics of the modulating frequency The root-mean-square (RMS) value of in excess of those permitted by these the inverse distance fields at a distance regulations. (See § 73.1570) of 1 kilometer from the antenna in all Maximum rated carrier power. The directions in the horizontal plane. The maximum power at which the trans- term ‘‘field strength’’ is synonymous mitter can be operated satisfactorily with the term ‘‘field intensity’’ as con- and is determined by the design of the tained elsewhere in this Part. transmitter and the type and number Equipment performance measurements. of vacuum tubes or other amplifier de- The measurements performed to deter- vices used in the last radio stage. mine the overall performance charac- Model I facility. A station operating teristics of a broadcast transmission in the 1605–1705 kHz band featuring system from point of program origina- fulltime operation with stereo, com- tion to sampling of signal as radiated. petitive technical quality, 10 kW day- (See § 73.1590) time power, 1 kW nighttime power, Experimental period. the time between non-directional antenna (or a simple 12 midnight local time and local sun- directional antenna system), and sepa- rise, used by AM stations for tests, rated by 400–800 km from other co- maintenance and experimentation. channel stations.

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Model II facility. A station operating tionable interference or objectionable in the 535–1605 kHz band featuring fading. fulltime operation, competitive tech- Proof of performance measurements or nical quality, wide area daytime cov- antenna proof of performance measure- erage with nighttime coverage at least ments. The measurements of field 15% of the daytime coverage. strengths made to determine the radi- Modulation dependent carrier level ation pattern or characteristics of an (MDCL) control technologies. Trans- AM directional antenna system. mitter control techniques that vary ei- Secondary service area. Means the ther the carrier power level or both the service area of a broadcast station carrier and sideband power levels as a served by the skywave and not subject function of the modulation level. to objectionable interference and in Nighttime. The period of time between which the signal is subject to intermit- local sunset and local sunrise. tent variations in strength. Nominal power. The antenna input Stereophonic channel. The band of power less any power loss through a audio frequencies from 50 to 10,000 Hz dissipative network and, for directional containing the stereophonic informa- antennas, without consideration of ad- tion which modulates the radio fre- justments specified in paragraphs (b)(1) quency carrier. and (b)(2) of § 73.51 of the rules. How- Stereophonic crosstalk. An undesired ever, for AM broadcast applications signal occurring in the main channel granted or filed before June 3, 1985, from modulation of the stereophonic nominal power is specified in a system channel or that occurring in the of classifications which include the fol- stereophonic channel from modulation lowing values: 50 kW, 25 kW, 10 kW, 5 of the main channel. kW, 2.5 kW, 1 kW, 0.5 kW, and 0.25 kW. Stereophonic pilot tone. An audio tone The specified nominal power for any of fixed or variable frequency modu- station in this group of stations will be lating the carrier during the trans- retained until action is taken on or mission of stereophonic programs. after June 3, 1985, which involves a Stereophonic separation. The ratio of change in the technical facilities of the the electrical signal caused in the right station. (or left) stereophonic channel to the Percentage modulation (amplitude) electrical signal caused in the left (or In a positive direction: right) stereophonic channel by the transmission of only a right (or left) M = MAX¥C × 100 signal. ————––—––— Sunrise and sunset. For each par- c ticular location and during any par- In a negative direction: ticular month, the time of sunrise and sunset as specified in the instrument of M = C¥MIN × 100 authorization (See § 73.1209). ————–—––— White area. The area or population c which does not receive interference- Where: free primary service from an author- M = Modulation level in percent. ized AM station or does not receive a MAX = Instantaneous maximum level of the signal strength of at least 1 mV/m from modulated radio frequency envelope. an authorized FM station. MIN = Instantaneous minimum level of the modulated radio frequency envelope. [47 FR 8587, Mar. 1, 1982, as amended at 47 FR C = (Carrier) level of radio frequency enve- 13164, Mar. 29, 1982; 47 FR 13812, Apr. 1, 1982; lope without modulation. 50 FR 18821, May 2, 1985; 50 FR 47054, Nov. 14, 1985; 56 FR 64856, Dec. 12, 1991; 62 FR 51058, Plate modulation. The modulation Sept. 30, 1997; 66 FR 20755, Apr. 25, 2001; 81 FR produced by introduction of the modu- 2759, Jan. 19, 2016; 82 FR 57882, Dec. 8, 2017] lating wave into the plate circuit of any tube in which the carrier fre- § 73.21 Classes of AM broadcast chan- quency wave is present. nels and stations. Primary service area. Means the serv- (a) Clear channel. A clear channel is ice area of a broadcast station in which one on which stations are assigned to the groundwave is not subject to objec- serve wide areas. These stations are

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