This subpart contains those rules which apply exclusively to the digital audio broadcasting (DAB) service, and are in addition to those rules in Subparts A, B, C, G and H which apply to AM and FM broadcast services, both commercial and noncommercial.

(a) DAB. Digital audio broadcast stations are those radio stations licensed by the Commission and use the In-band On-channel (“IBOC”) system for broadcasting purposes.

(b) In Band On Channel DAB System. A technical system in which a station's digital signal is broadcast in the same spectrum and on the same channel as its analog signal.

(c) Hybrid DAB System. A system which transmits both the digital and analog signals within the spectral emission mask of a single AM or FM channel.

(d) Extended hybrid operation. An enhanced mode of FM IBOC DAB operation which includes additional DAB subcarriers transmitted between the analog FM signal and the inner edges of the primary DAB sidebands.

(e) Primary AM DAB Sidebands. The two groups of hybrid AM IBOC DAB subcarriers which are transmitted 10 to 15 kHz above carrier frequency (the upper primary DAB sideband), and 10 to 15 kHz below carrier frequency (the lower primary DAB sideband).

(f) Multicasting. Subdividing the digital bitstream into multiple channels for additional audio programming uses.

(g) Datacasting. Subdividing the digital bitstream into multiple channels for additional data or information services uses.

(h) All-digital AM station. An AM station broadcasting an IBOC waveform that consists solely of digitally modulated subcarriers and the unmodulated AM carrier.

(a) Broadcast radio stations using IBOC must transmit at least one over-the-air digital audio programming stream at no direct charge to listeners. In addition, a hybrid broadcast radio station must simulcast its analog audio programming on one of its digital audio programming streams. The DAB audio programming stream that is provided pursuant to this paragraph (a) must be at least comparable in sound quality with a standard analog broadcast.

(b) Emergency information. The emergency information requirements found in § 73.1250 shall apply to all free DAB programming streams.

(a) The licensee of an AM or FM station, or the permittee of a new AM or FM station which has commenced program test operation pursuant to § 73.1620, may commence hybrid IBOC DAB operation with digital facilities which conform to the technical specifications specified for hybrid DAB operation in the (2002) First Report and Order in MM Docket No. 99-325, as revised in the Media Bureau's subsequent Order in MM Docket No. 99-325. In addition, the licensee of an AM station, or the permittee of a new AM station that has commenced program test authority pursuant to § 73.1620, may, with reasonable notice to listeners, commence all-digital IBOC operation with digital facilities that conform to the requirements set out in the (2020) Report and Order in MB Docket No. 19-311 and MB Docket No. 13-249. An AM or FM station may transmit IBOC signals during all hours for which the station is licensed to broadcast.

(b) In situations where interference to other stations is anticipated or actually occurs, hybrid AM licensees may, upon notification to the Commission, reduce the power of the primary DAB sidebands by up to 6 dB. All-digital AM licensees, may, upon notification to the Commission, reduce the power of the secondary and tertiary sidebands by up to 6 dB, even if doing so results in non-compliance with § 73.1560(a)(1). Any greater reduction of sideband power requires prior authority from the Commission via the filing of a request for special temporary authority or an informal letter request for modification of license.

(c) Hybrid IBOC AM stations must use the same licensed main or auxiliary antenna to transmit the analog and digital signals.

(d) FM stations may transmit hybrid IBOC signals in combined mode; i.e., using the same antenna for the analog and digital signals; or may employ separate analog and digital antennas. Where separate antennas are used, the digital antenna:

(1) Must be a licensed auxiliary antenna of the station;

(2) Must be located within 3 seconds latitude and longitude from the analog antenna;

(3) Must have a radiation center height above average terrain between 70 and 100 percent of the height above average terrain of the analog antenna.

(a) Hybrid AM and FM licensees must electronically file a digital notification to the Commission in Washington, DC, within 10 days of commencing IBOC digital operation.

(1) All-digital licensees must file a digital notification within 10 days of the following changes:

(i) Any reduction in nominal power of an all-digital AM station;

(ii) A transition from enhanced to core-only operating mode; or

(iii) A reversion from all-digital to hybrid or analog operation.

(2) All-digital licensees will not be permitted to commence operation sooner than 30 calendar days from public notice of digital notification of the following changes:

(i) The commencement of new all-digital operation;

(ii) An increase in nominal power of an all-digital AM station; or

(iii) A transition from core-only to enhanced operating mode.

(b) Every digital notification must include the following information:

(1) The call sign and facility identification number of the station;

(2) If applicable, the date on which the new or modified IBOC operation commenced or ceased;

(3) The name and telephone number of a technical representative the Commission can call in the event of interference;

(4) A certification that the operation will not cause human exposure to levels of radio frequency radiation in excess of the limits specified in § 1.1310 of this chapter and is therefore categorically excluded from environmental processing pursuant to § 1.1306(b) of this chapter. Any station that cannot certify compliance must submit an environmental assessment (“EA”) pursuant to § 1.1311 of this chapter and may not commence IBOC operation until such EA is ruled upon by the Commission.

(c) Each AM digital notification must also include the following information:

(1) A certification that the IBOC DAB facilities conform to applicable nominal power limits and emissions mask limits;

(2) The nominal power of the station; if separate analog and digital transmitters are used, the nominal power for each transmitter;

(3) If applicable, the amount of any reduction in an AM station's digital carriers;

(4) For all-digital stations, the type of notification (all-digital notification, increase in nominal power, reduction in nominal power, transition from core-only to enhanced, transition from enhanced to core-only, reversion from all-digital to hybrid or analog operation);

(5) For all-digital stations, if a notification of commencement of new all-digital service or a nominal power change, whether the station is operating in core-only or enhanced mode; and

(6) For all-digital stations, a certification that the all-digital station complies with all Emergency Alert System (EAS) requirements in part 11 of this chapter.

(d) Each FM digital notification must also include the following information:

(1) A certification that the IBOC DAB facilities conform to the HD Radio emissions mask limits;

(2) FM digital effective radiated power used and certification that the FM analog effective radiated power remains as authorized;

(3) If applicable, the geographic coordinates, elevation data, and license file number of the auxiliary antenna employed by an FM station as a separate digital antenna; and

(4) If applicable, for FM systems employing interleaved antenna bays, a certification that adequate filtering and/or isolation equipment has been installed to prevent spurious emissions in excess of the limits specified in § 73.317.