§ 73.317   FM transmission system requirements.

   (a) FM broadcast stations employing transmitters authorized after
   January 1, 1960, must maintain the bandwidth occupied by their
   emissions in accordance with the specification detailed below. FM
   broadcast stations employing transmitters installed or type accepted
   before January 1, 1960, must achieve the highest degree of compliance
   with these specifications practicable with their existing equipment. In
   either case, should harmful interference to other authorized stations
   occur, the licensee shall correct the problem promptly or cease
   operation.

   (b) Any emission appearing on a frequency removed from the carrier by
   between 120 kHz and 240 kHz inclusive must be attenuated at least 25 dB
   below the level of the unmodulated carrier. Compliance with this
   requirement will be deemed to show the occupied bandwidth to be 240 kHz
   or less.

   (c) Any emission appearing on a frequency removed from the carrier by
   more than 240 kHz and up to and including 600 kHz must be attenuated at
   least 35 dB below the level of the unmodulated carrier.

   (d) Any emission appearing on a frequency removed from the carrier by
   more than 600 kHz must be attenuated at least 43 + 10 Log10 (Power, in
   watts) dB below the level of the unmodulated carrier, or 80 dB,
   whichever is the lesser attenuation.

   (e) Preemphasis shall not be greater than the impedance-frequency
   characteristics of a series inductance resistance network having a time
   constant of 75 microseconds. (See upper curve of Figure 2 of § 73.333.)

   [ 51 FR 17028 , May 8, 1986]

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