§ 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]

   return arrow Back to Top