(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 Sec. 73.1620, may commence interim hybrid IBOC DAB operation with digital facilities which conform to the technical specifications specified for hybrid DAB operation in the 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. FM stations are permitted to operate with hybrid digital effective radiated power equal to one percent (-20 decibels below carrier (dBc)) of authorized analog effective radiated power and may operate with up to ten percent (-10 dBc) of authorized analog effective radiated power in accordance with the procedures set forth in the Media Bureau's Order in MM Docket No. 99-325. 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, AM licensees may, upon notification to the Commission, reduce the power of the primary DAB sidebands by up to 6 dB. 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) Licensees must provide notification to the Commission in Washington, DC, within 10 days of commencing IBOC digital operation. The notification must include the following information:
(1) Call sign and facility identification number of the station;
(2) Date on which IBOC operation commenced;
(3) Certification that the IBOC DAB facilities conform to permissible hybrid specifications;
(4) Name and telephone number of a technical representative the Commission can call in the event of interference;
(5) FM digital effective radiated power used and certification that the FM analog effective radiated power remains as authorized;
(6) Transmitter power output; if separate analog and digital transmitters are used, the power output for each transmitter;
(7) If applicable, any reduction in an AM station's primary digital carriers;
(8) 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;
(9) 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 Sec. 73.317;
(10) A certification that the operation will not cause human exposure to levels of radio frequency radiation in excess of the limits specified in Sec. 1.1310 of this chapter and is therefore categorically excluded from environmental processing pursuant to Sec. 1.1306(b) of this chapter. Any station that cannot certify compliance must submit an environmental assessment (``EA'') pursuant to Sec. 1.1311 of this chapter and may not commence IBOC operation until such EA is ruled upon by the Commission. [72 FR 45692, Aug. 15, 2007, as amended at 75 FR 17877, Apr. 8, 2010]