Section 74.637 - Emissions and emission limitations(a) The mean power of emissions shall be attenuated below the mean transmitter power (PMEAN) in accordance with the following schedule: (1) When using frequency modulation: (i) On any frequency removed from the assigned (center) frequency by more than 50% up to and including 100% of the authorized bandwidth: At least 25 dB in any 100 kHz reference bandwidth (BREF);(ii) On any frequency removed from the assigned (center) frequency by more than 100% up to and including 250% of the authorized bandwidth: At least 35 dB in any 100 kHz reference bandwidth;(iii) On any frequency removed from the assigned (center) frequency by more than 250% of the authorized bandwidth: At least 43 + 10 log10 (PMEAN in watts) dB, or 80 dB, whichever is the lesser attenuation, in any 100 kHz reference bandwidth.(2) When using transmissions employing digital modulation techniques:(i) For operating frequencies below 15 GHz, in any 4 kHz reference bandwidth (BREF), the center frequency of which is removed from the assigned frequency by more than 50 percent up to and including 250 percent of the authorized bandwidth: As specified by the following equation but in no event less than 50 decibels: A = 35 + 0.8 (G - 50) + 10 Log10 B.
(Attenuation greater than 80 decibels is not required.)
Where:
A = Attenuation (in decibels) below the mean output power level.
G = Percent removed from the carrier frequency.
B = Authorized bandwidth in megahertz.
(ii) For operating frequencies above 15 GHz, in any 1 MHz reference bandwidth (BREF), the center frequency of which is removed from the assigned frequency by more than 50 percent up to and including 250 percent of the authorized bandwidth: As specified by the following equation but in no event less than 11 decibels: A = 11 + 0.4 (G-50) + 10 Log10 B.
(Attenuation greater than 56 decibels is not required.)
(iii) In any 4 kHz reference bandwidth (BREF), the center frequency of which is removed from the assigned frequency by more than 250 percent of the authorized bandwidth: At least 43 + 10 Log10 (PMEAN in watts) decibels, or 80 decibels, whichever is the lesser attenuation.(3) Amplitude Modulation. For vestigial sideband AM video: On any frequency removed from the center frequency of the authorized band by more than 50%: at least 50 dB below peak power of the emission.(b) For all emissions not covered in paragraph (a) of this section, the peak power of emissions shall be attenuated below the peak envelope transmitter power (PPEAK) in accordance with the following schedule: (1) On any frequency 500 Hz inside the channel edge up to and including 2500 Hz outside the same edge, the following formula will apply: A = 29 Log10 [(25/11)[(D + 2.5 - (W/2)]2] dB
(Attenuation greater than 50 decibels is not required.)
Where:
A = Attenuation (in dB) below the peak envelope transmitter power.
D = The displacement frequency (kHz) from the center of the authorized bandwidth.
W = the channel bandwidth (kHz).
(2) On any frequency removed from the channel edge by more than 2500 Hz: At least 43 + 10 Log10 (PPEAK in watts) dB.(c) For purposes of compliance with the emission limitation requirements of this section: (1) If the transmitter modulates a single carrier, digital modulation techniques are considered as being employed when digital modulation occupies 50 percent or more of the total peak frequency deviation of a transmitted radio frequency carrier. The total peak frequency deviation will be determined by adding the deviation produced by the digital modulation signal and the deviation produced by any frequency division multiplex (FDM) modulation used. The deviation (D) produced by the FDM signal must be determined in accordance with § 2.202(f) of this chapter.(2) If the transmitter modulates two or more carriers, with at least one using digital modulation and one using frequency or other analog modulation, digital modulation techniques are considered as being employed when the necessary bandwidth of the digital signal(s) is 50 percent or more of the aggregate bandwidth of the system, comprising the digital necessary bandwidth(s), the analog necessary bandwidth(s), and any bandwidth(s) between the digital and analog necessary bandwidths. In this case, the aggregate bandwidth shall be used for the authorized bandwidth (B) in paragraph (a) of this section, and for purposes of compliance with the bandwidth limitations in paragraph (g) of this section and in § 74.602 of this subpart; and the sum of the powers of the analog and digital signals shall be used for mean transmitter power (PMEAN) in paragraph (a) or the peak envelope transmitter power (PPEAK) in paragraph (b) of this section, and for purposes of compliance with the power limitations in § 74.636 of this subpart.(3) For demonstrating compliance with the attenuation requirements for frequency modulation and digital modulation in paragraph (a) of this section, the resolution bandwidth (BRES) of the measuring equipment used for measurements removed from the center frequency by more than 250 percent of the authorized bandwidth shall be 100 kHz for operating frequencies below 1 GHz, and 1 MHz for operating frequencies above 1 GHz. The resolution bandwidth for frequencies removed from the center frequency by less than 250 percent of the authorized bandwidth shall be the reference bandwidth (BREF) specified in the individual emission limitations, but may be reduced to not less than one percent of the authorized bandwidth (B), adjusted upward to the nearest greater resolution bandwidth available on the measuring equipment. In all cases, if BRES and BREF are not equal, then the attenuation requirement must be increased (or decreased) as determined by a factor of 10 log10 [(BREF in megahertz)/(BRES in megahertz)] decibels, where a positive factor indicates an increase in the attenuation requirement and a negative factor indicates a decrease in the attenuation requirement.(4) Stations licensed pursuant to an application filed before March 17, 2005, using equipment not conforming with the emission limitations specified above, may continue to operate indefinitely in accordance with the terms of their current authorizations, subject to periodic renewal. Existing equipment and equipment of product lines in production before April 16, 2003, authorized via certification or Declaration of Conformity before March 17, 2005, for equipment not conforming to the emission limitations requirements specified above, may continue to be manufactured and/or marketed, but may not be authorized for use under a station license except at stations licensed pursuant to an application filed before March 17, 2005. Any non-conforming equipment authorized under a station license, and replaced on or after March 17, 2005, must be replaced by conforming equipment. Note 1 to paragraph (c)(4): The Declaration of Conformity procedure has been replaced by Supplier's Declaration of Conformity. See § 2.950 of this chapter.
(d) In the event that interference to other stations is caused by emissions outside the authorized channel, the FCC may require greater attenuation than that specified in paragraph (b) of this section.(e) The following limitations also apply to the operation of TV microwave booster stations: (1) The booster station must receive and amplify the signals of the originating station and retransmit them on the same frequency without significantly altering them in any way. The characteristics of the booster transmitter output signal shall meet the requirements applicable to the signal of the originating station.(2) The licensee is responsible for correcting any condition of interference that results from the radiation of radio frequency energy outside the assigned channel. Upon notice by the FCC to the station licensee that interference is being caused, operation of the apparatus must be immediately suspended and may not be resumed until the interference has been eliminated or it can be demonstrated that the interference is not due to spurious emissions. However, short term test transmissions may be made during the period of suspended operation to determine the efficacy of remedial measures.(3) In each instance where suspension of operation is required, the licensee must submit a full report to the FCC after operation is resumed. The report must contain details of the nature of the interference, the source of interfering signals, and the remedial steps taken to eliminate the interference.(f) In the event a station's emissions outside its authorized channel cause harmful interference, the Commission may require the licensee to take such further steps as may be necessary to eliminate the interference.(g) The maximum bandwidth which will be authorized per frequency assignment is set out in the table which follows. Regardless of the maximum authorized bandwidth specified for each frequency band, the Commission reserves the right to issue a license for less than the maximum bandwidth if it appears that less bandwidth would be sufficient to support an applicant's intended communications. Table 1 to Paragraph (g)
| Frequency Band (MHz) | Maximum authorized bandwidth (MHz) |
| 1,990 to 2,110 | 18 |
| 6,425 to 6,525 | 25 |
| 6,875 to 7,125 | 25 |
| 12,700 to 13,250 | 25 |
| 17,700 to 19,700 | 80 |
45 FR 78692, Nov. 26, 1980, as amended at 48 FR 50734, Nov. 3, 1983; 49 FR 7131, Feb. 27, 1984; 49 FR 37778, Sept. 26, 1984; 50 FR 7342, Feb. 22, 1985; 50 FR 34150, Aug. 23, 1985; 50 FR 48600, Nov. 26, 1985; 52 FR 7142, Mar. 9, 1987; 58 FR 51251, Oct. 1, 1993; 68 FR 12769, Mar. 17, 2003; 82 FR 50836, Nov. 2, 2017