Engineers duel over IBOC power boost


Comments are flowing in to the FCC over whether to grant a request to increase the maximum power for FM digital channels to improve coverage and building penetration. Engineers are checking in on both sides of the argument.

Radio giants Clear Channel and CBS Radio were joined by 14 other radio groups and four equipment manufacturers in requesting that the FCC increase the maximum permissible digital operating power of FM stations from the current limit of 1% of a station’s authorized analog power to 10%. The move was backed by a technical report prepared by iBiquity Digital Corporation, which licenses the HD Radio technology used for in-band, on-channel (IBOC) digital broadcasting.

But National Public Radio also submitted a technical report and said it would conduct additional testing on power levels and interference. The FCC sought comments on whether it should go ahead with a provisional power increase for IBOC signals, or wait for the further NPR studies. And it asked what standards should be set to protect stations on first adjacent channels from interference – and should those protections extend to LPFMs?

Independent engineer and consultant Barry McLarnon said the answer on whether to hold off is “an unequivocal yes.” In his view, nothing in the record supports the move to allow all stations to increase digital power. “Ther is no headroom for any power increase in many cases. Clearly, this matter should be dealt with ona case-by-case basis,” he told the FCC.

Engineer Brian Kirby took issue with the conclusions of the NPR study and said what it really showed was that most of the interference problems would be in the mobile environment, where people have long been used to FM reception interference, and that most of the audio impairments that NPR Labs is concerned about would be eliminated when the broadcast is received in HD Radio, so the listeners most concerned about the impairments would benefit from higher power.

“Should the aching loose tooth be pulled slowly and discussed ad nauseam or should it be pulled in one clean swoop. Increasing to -10dBc, the pain in this case is minor occasional spluttering that will in reality only be clearly heard when listening to ‘quiet’ program material in limited low signal areas in the primary contour. At any one time, the vast majority of the listening audience within the primary service contour will not experience, to any the significant extent, the audio impairments mentioned. What NPR labs has done with the publication of the audio recordings, has shown the need to increase the IBOC digital signal level to -10dBc and to increase it now,” Kirby declared.

Simmons Media Group filed its opposition to any power increase until the further NPR studies are released in September or thereafter. Also opposing an immediate power increase were three owners of large groups of non-commercial FM stations and translators: Calvary Chapel of Twin Falls, Positive Alternative Radio and Creative Educational Media Corporation.

Livingston Radio Company, licensee of WHMI-FM Howell, MI, complained of the interference it is already receiving from the digital signal of adjacent channel WBCT-FM Grand Rapids, MI, a grandfathered super-power station. Livingston President and General Manager Greg Jablonski said he could see both sides of the issue, since higher power could improve digital reception. “The jury is still out on digital radio, with the likelihood of its acceptance by the public dropping every day,” he wrote. However, Jablonski warned that a “hasty digital fix” which harms the legacy analog FM service “doesn’t pass my cost-benefit analysis.”

Comments in the latest round of Docket 99-325 are due July 6th, with reply comments due July 17th.