The FCC adopted rules for the digital operation of FM radio stations (known as HD Radio or the Ibiquity In Band On Channel system - IBOC for short) in 2007 and allowed the Media Bureau to amend those rules as technical developments warranted. In 2010, the Bureau authorized an increase in the power level of the digital portion of the FM signal by 6 db in all cases, and up to 10 db upon a showing that such an increase would not cause significant interference to adjacent channel stations (see our summary here). As the digital signal is carried on "sidebands" of the analog signal, which operate on part of a station's assigned frequency that is closer to adjacent channel radio stations, an increase in power on these sidebands has the potential for causing interference to closely spaced stations. In a Public Notice released today, the FCC asked for comments on whether it should allow stations to increase power at different levels on each sideband. As set out by the Bureau, in some situations, a station may be closely spaced to another station on one side of its frequency, on a channel either higher or lower than the one on which the station operates, but not on the other side of its channel. By increasing power on only the sideband furthest from the adjacent channel station, the station can protect the adjacent channel station, yet still enjoy the possibility of expanded coverage that the higher power provides.
As set forth in the Notice, this proposal is advanced by Ibiquity (the company that holds the patent on the digital radio system) and NPR, which has been very active in promoting its use. According to studies that they have produced (and which are linked to in the public notice), a digital operation with greater power to one sideband than another is technically possible. The FCC asks if it is a good idea, and gives interested parties 21 days to file comments (measured from the date that this notice is published in the Federal Register) and an additional 14 days to file replies to the initial comments. In the past, we have found digital radio operations to be among the most controversial topics about which we write, with some who feel that the system is not working and will never work, and others who see much promise in the digital sound and multiple channels allowed by the system. We look forward to seeing the comments filed in this proceeding, to see whether these attitudes continue to persist within the industry.