Sec. 21.106  Emission limitations.

    (a) The mean power of emissions shall be attenuated below the mean 
output power of the transmitter in accordance with the following 
schedule:
    (1) When using transmissions other than those employing digital 
modulation techniques:
    (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 Log10 
(mean output power in watts) decibels, or 80 decibels, whichever is the 
lesser attenuation.
    (2) When using transmissions employing digital modulation techniques 
(see Sec. 21.122(b)) in situations other than those covered by paragraph 
(a)(3) of this section:
    (i) For operating frequencies below 15 GHz, in any 4 kHz 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 50 decibels. A=35+0.8(P;minus;50)+10 Log10 B. 
(Attenuation greater than 80 decibels is not required.)

where:

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

    (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.
    (b) When an emission outside of the authorized bandwidth causes 
harmful interference, the Commission may, at its discretion, require 
greater attenuation than specified in paragraph (a) of this section.
[ 44 FR 60534 , Oct. 19, 1979, as amended at  46 FR 23450 , Apr. 27, 1981; 
 52 FR 23550 , June 23, 1987;  61 FR 26675 , May 28, 1996]