Sec. 74.535  Emission and bandwidth.

    (a) For frequency modulation, the mean power of emissions shall be 
attenuated below the mean transmitter power (P) in accordance with the 
following schedule:
    (1) On any frequency removed from the assigned frequency by more 
than 50% and up to 100% of the authorized bandwidth: at least 25 dB.
    (2) On any frequency removed from the assigned frequency by more 
than 100% and up to 150% of the authorized bandwidth: at least 35 dB.
    (3) On any frequency removed from the assigned frequency by more 
than 150% of the authorized bandwidth: at least 43 + 10 Log(P) dB.
    (b) For all emissions except frequency modulation, the peak power of 
emissions shall be attenuated below the peak envelope transmitter power 
(P) 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:
[GRAPHIC] [TIFF OMITTED] TC13NO91.023


or 50 dB whichever is the lesser attenuation. Where: D is the 
displacement frequency (kHz) from the center of the authorized 
bandwidth; and W is the channel bandwidth (kHz).
    (2) On any frequency removed from the channel edge by more than 2500 
Hz: At least 43+10 Log (P) dB.
    (c) 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.
    (d) For operation in the 18 GHz band: Aural broadcast STL, intercity 
relay stations and booster stations may be authorized to employ either 
digital or frequency modulation.
    (e) For operation in the 18 GHz band: The mean power of emission 
shall be attenuated below the mean output power of the transmitter in 
accordance with the following schedule:
    (1) When using frequency modulation:
    (i) On any frequency removed from the assigned frequency by more 
than 50 percent up to and including 100 percent of the authorized 
bandwidth: At least 25 decibels;
    (ii) On any frequency removed from the assigned frequency by more 
than 100 percent up to and including 250 percent of the authorized 
bandwidth: At least 35 decibels;
    (iii) On any frequency removed from the assigned frequency by more 
than 250 percent of the authorized bandwidth: At least 43+10 log!10 
(mean output power in watts) decibels, or 80 decibels, whichever is the 
lesser attenuation.
    (2) When using digital modulation:
    (i) In any 1 MHz band, 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 (P-50) + 10 log10 B

Where:
A = Attenuation (in decibels) below the mean output power level.
P = Percent removed from the carrier frequency.
B = Authorized bandwidth in MHz.

    [Attenuation greater than 56 decibels is not required.]
    (ii) In any 4 kHz band, 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 (mean output power in 
watts) decibels, or 80 decibels, whichever is the lesser attenuation.
    (f) For operation in the 18 GHz band: When an emission outside of 
the authorized bandwidth causes harmful interference, the Commission 
may, at its discretion require greater attenuation than specified above.
    (g) The following limitations apply to the operation of aural 
broadcast microwave booster stations:

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    (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.

[ 28 FR 13716 , Dec. 14, 1963, as amended at  48 FR 50332 , Nov. 1, 1983;  49 FR 7130 , Feb. 27, 1984;  49 FR 37777 , Sept. 26, 1984;  50 FR 48599 , Nov. 
26, 1985]