§ 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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