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 Secs. 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

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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]