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: