The FCC has approved In-Band On-Channel (IBOC) digital radio operation for AM (daytime and nighttime) and FM broadcast stations.
Current Information for Licensees
- To obtain a list of stations authorized for "hybrid" operation (analog + digital signals), select one of the following links: [ AM  | FM  ].
- Guidance Provided to FM Licensees Regarding Operations with Increased Digital Power (MM Docket No. 99-325), Public Notice, MM Docket 99-325 ,
DA 10-866, released May 17, 2010. [ PDF  | Word  ].
- Digital power increase for FM stations approved. Digital Audio Broadcasting Systems and Their Impact on the Terrestrial Radio Broadcast Service, Order, MM Docket 99-325 ,
DA 10-208, released January 29, 2010. [ PDF  | Word  ]. FM stations operating in excess of the station's authorized class may use the FM Super-Powered Maximum Digital ERP Calculator . Other FM stations, see the Order for the calculation procedure. News Release summary, [ PDF  | Word  ], released January 29, 2010. Procedure for Filing STA Requests for Increased Digital FM Power .
What Is IBOC Digital Radio?
IBOC refers to the method of transmitting a digital radio broadcast signal centered on the same frequency as the AM or FM station's present frequency. For FM stations, the transmission of the digital signal occupies the sidebands above and below the center FM frequency (e.g., 97.9 MHz). AM band transmissions also place the digital signal in sidebands above and below the existing AM carrier frequency. By this means, the AM or FM station digital signal is transmitted in addition to the existing analog signal. In both instances, the digital emissions fall within the spectral emission mask of the AM or FM channel (see 47 CFR Sections 73.44  and 73.317 ).
The present IBOC system is referred to as a "hybrid" since it is neither fully analog nor fully digital. During hybrid operation, existing receivers still continue to receive the analog (non-digital) signal. New receivers will incorporate both modes of reception, where the receiver will automatically switch to the analog signal if the digital signal cannot be decoded or is lost by the receiver.
Technical information about IBOC can be found on Ibiquity's website, http://www.ibiquity.com/ .