Broadcaster Divide Deepens as FCC Weighs Digital Power Issue

July 15, 2009


A flurry of filings arrived at the FCC last week as the window for comments on specific issues surrounding a proposed 10dB increase of FM IBOC digital carriers drew to a close. While Commission staffers probably weren't surprised by the general positions adopted in those documents, they're sure to notice a deepening schism between IBOC proponents regarding how a switch to higher digital signal levels ought to be handled.

The bone of contention concerns potential interference between beefed-up digital carriers and first-adjacent signals. That issue emerged from findings of a past NPR Labs study designed to deliver real-world performance data for IBOC digital hybrid transmission under a variety of conditions. Based on its initial work, NPR Labs is engaged in a follow-up study that seeks to determine maximal power levels for improved digital coverage while protecting analog FM signals, including subcarrier transmissions, from interference. The study is also exploring the minimum spacing distances needed to protect analog signals from boosted digital operations, with preliminary findings expected in about 60 days.

Among those advocating full speed ahead on a one-size-fits-all approach were comments filed separately by the NAB and the "joint commenters" (JC), an amalgam of broadcast groups heavily invested in an HD Radio infrastructure along with four broadcast equipment manufacturers. Both urged the FCC to grant an immediate 10dB increase in digital carrier power based on three major premises:

  • The current IBOC digital carrier level is seriously deficient in terms of matching analog coverage, particularly in terms of building penetration.
  • Because the first HD portable receivers are now moving to market (including the ballyhooed Microsoft Zune), public perception of the technology by early adopters is likely to be marred by poor digital reception unless quick action is taken to boost digital signal levels.
  • The adjacent-channel interference potential of a 10x increase in digital carrier power is negligible, based on the experience of selected JP stations already operating at elevated levels under STAs previously granted by the FCC, as well as the absence of any formal complaints to date regarding adjacent channel interference by an FM IBOC digital signal. Any future complaints could be addressed by the FCC on a case by case basis.

    Ibiquity Digital, which obviously has an enormous stake in the FCC decision, took just a slightly more understated approach, employing similar arguments and urging the Commission to approve an immediate increase of 6dB, with an eventual increase of an additional 4dB when specification changes are "finalized."

    Among a number of notable entities espousing a more deliberate approach to the issue were

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    For its part, NPR indicated that while its member stations have an enormous investment in IBOC digital technology, evidence of significant interference potential already exists, and that forthcoming data is essential in establishing clear parameters for dealing with issue.

    Perhaps one of the most striking points made by NPR involves the burden of proof in interference cases. While proponents of an across-the-board increase suggest that any resulting interference could be addressed by the Commission after the fact, such an approach would serve to shift the burden to the plaintiff station, imposing consulting engineering expenses that could prove onerous for small LPFM and NCE stations. NPR's comments suggest that the burden rightly ought to be borne by the station boosting their facility, as they currently are in the case of analog power increases.

    NPR also notes a serious question as to whether analog listeners would perceive digital interference as such. Since adjacent channel digital interference tends to manifest as white noise in a receiver, it is suggested that the average listener is far more likely to conclude that the desired station's signal is simply too weak to listen to, resulting in tune-out.

    Fundamentally, both sides agree that increases to IBOC digital carrier levels are needed to ensure a reasonable level of service, and that such a move needs to come quickly. NPR even went so far as to offer a simple algorithm for establishing elevated digital carrier levels on an interim case-by-case basis.

    But the argument that a decision delay of another 60 days could irreparably tarnish HD Radio's future shouldn't outweigh the documented interference potential poised by a cookie-cutter approach. The Commission has a compelling obligation to act in the public interest, and that includes assuring a vast majority of citizens that depend on analog FM today will continue to so without impediment for the immediate future.

    It's notoriously difficult to put toothpaste back in the tube once it's been squeezed out. Let's hope the FCC recognizes that it's better to wait 60 days and have the best available information before making a key decision that could impact FM broadcasters for years to come.



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