Sec.  73.319   FM multiplex subcarrier technical standards.

   (a) The technical specifications in this Section apply to all transmissions
   of FM multiplex subcarriers except those used for stereophonic sound
   broadcasts under the provisions of  Sec. 73.322.

   (b) Modulation. Any form of modulation may be used for subcarrier operation.

   (c) Subcarrier baseband. (1) During monophonic program transmissions,
   multiplex subcarriers and their significant sidebands must be within the
   range of 20 kHz to 99 kHz.

   (2) During stereophonic sound program transmissions (see  Sec. 73.322), multiplex
   subcarriers and their significant sidebands must be within the range of 53
   kHz to 99 kHz.

   (3) During periods when broadcast programs are not being transmitted,
   multiplex subcarriers and their significant sidebands must be within the
   range of 20 kHz to 99 kHz.

   (d) Subcarrier injection. (1) During monophonic program transmissions,
   modulation of the carrier by the arithmetic sum of all subcarriers may not
   exceed 30% referenced to 75 kHz modulation deviation. However, the
   modulation of the carrier by the arithmetic sum of all subcarriers above 75
   kHz may not modulate the carrier by more than 10%.

   (2) During stereophonic program transmissions, modulation of the carrier by
   the arithmetic sum of all subcarriers may not exceed 20% referenced to 75
   kHz modulation deviation. However, the modulation of the carrier by the
   arithmetic sum of all subcarriers above 75 kHz may not modulate the carrier
   by more than 10%.

   (3) During periods when no broadcast program service is transmitted,
   modulation of the carrier by the arithmetic sum of all subcarriers may not
   exceed 30% referenced to 75 kHz modulation deviation. However, the
   modulation of the carrier by the arithmetic sum of all subcarriers above 75
   kHz may not modulate the carrier by more than 10%.

   (4) Total modulation of the carrier wave during transmission of multiplex
   subcarriers used for subsidiary communications services must comply with the
   provisions  Sec. 73.1570(b).

   (e) Subcarrier generators may be installed and used with a type accepted FM
   broadcast transmitter without specific authorization from the FCC provided
   the generator can be connected to the transmitter without requiring any
   mechanical or electrical modifications in the transmitter FM exciter
   circuits.

   (f) Stations installing multiplex subcarrier transmitting equipment must
   ensure the proper suppression of spurious or harmonic radiations. See
    Sec.  Sec. 73.317, 73.1590 and 73.1690. If the subcarrier operation causes the
   station's transmissions not to comply with the technical provisions for FM
   broadcast stations or causes harmful interference to other communication
   services, the licensee or permittee must correct the problem promptly or
   cease operation. The licensee may be required to verify the corrective
   measures with supporting data. Such data must be retained at the station and
   be made available to the FCC upon request.

   [ 48 FR 28455 , June 22, 1983, as amended at  48 FR 37216 , Aug. 17, 1983;  49 FR 15080 , Apr. 17, 1984;  49 FR 38131 , Sept. 27, 1984;  50 FR 1534 , Jan. 11,
   1985;  51 FR 17029 , May 8, 1986;  57 FR 48333 , Oct. 23, 1992]