47 CFR 73.665 - Use of TV aural baseband subcarriers.
Licensees of TV broadcast stations may transmit, without further authorization from the FCC, subcarriers and signals within the composite baseband for the following purposes:
(a) Stereophonic (biphonic, quadraphonic, etc.) sound programs under the provisions of §§ 73.667 and 73.669.
(b) Transmission of signals relating to the operation of TV stations, such as relaying broadcast materials to other stations, remote cueing and order messages, and control and telemetry signals for the transmitting system.
(c) Transmission of pilot or control signals to enhance the station's program service such as (but not restricted to) activation of noise reduction decoders in receivers, for any other receiver control purpose, or for program alerting and program identification.
(d) Subsidiary communications services.