§  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 § 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 § 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 § 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 § § 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]