In recent comments filed with the FCC regarding how best to implement a proposed increase in IBOC digital signal power, NPR labs suggested a method by which stations could determine a level of increase that would assure compliance with existing minimum interference protection requirements. NPR engineers noted that this methodology might serve as an interim means of allowing stations to establish a "safe" threshold for boosting digital signals in the short term while ongoing studies gather data to determine if more dramatic increases can be accommodated without causing harmful interference to first-adjacent channel analog signals.
In an impressive collaboration with consulting engineers Cavell & Mertz, calculations using the suggested algorithm were run for all U.S. FM stations. Data identifying a proponent station's conditions for each protected first-adjacent station is presented in two tiers: "Worst Case" being the most-critical protection and "Second Worst Case" being the second-most critical protection. An easy-to-use lookup table is available for public access on the Web, along with supporting explanations and documentation.
NPR Labs says the information could be valuable in considering other techniques to increase the allowable IBOC power without increasing interference. To learn more, as well as to see how your station might fare, go to NPR Lab's distribution site.