Section 73.404 - [Effective on an indefinitely defined date ] IBOC DAB operation(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.(e) Except stations operating on Channels 296-300 (107.1-107.9 MHz), FM stations may transmit hybrid IBOC signals with asymmetric power on the digital sidebands, as defined in § 73.402(i) . Stations operating on Channels 296-300 (107.1-107.9 MHz) may seek an experimental authorization to transmit hybrid IBOC signals with asymmetric power on the digital sidebands.(f) All FM stations transmitting hybrid IBOC signals may operate with total digital effective radiated power of up to -14 dBc. No station may operate its digital carriers with a total effective radiated power in excess of -10 dBc. A station planning to operate with a total digital effective radiated power in excess of -14 dBc must certify compliance with table 1 to this paragraph (f) by calculating the F(50,10) signal strength of its analog signal at the first adjacent station's F(50,50) 60 dB[MICRO] contour. Compliance with this table must be established for the upper and lower IBOC digital sidebands separately. All calculations must be made using the standard FCC contour prediction methodology. Table 1 to Paragraph (f) -Maximum Permissible FM Digital ERP per Sideband
| IBOC station's F(50,10) field strength at the upper or lower first-adjacent station's analog 60 dB[MICRO] F(50,50) contour | Maximum permissible FM digital ERP for the respective (upper or lower) sideband |
| 51.2 dB[MICRO] and above | -17 dBc. |
| 50.7 dB[MICRO] to 51.1 dB[MICRO] | -16 dBc. |
| 50.3 dB[MICRO] to 50.6 dB[MICRO] | -15 dBc. |
| 49.6 dB[MICRO] to 50.2 dB[MICRO] | -14 dBc. |
| 49.5 dB[MICRO] or less | -13 dBc. |
72 FR 45692 , Aug. 15, 2007, as amended at 75 FR 17877 , Apr. 8, 2010; 85 FR 18151 , Apr. 1, 2020; 85 FR 78027 , Dec. 3, 2020 85 FR 18151 , 6/1/2020; 85 FR 78027 , 1/4/2021; 89 FR 84104 , effective date to be determined