Friday, October 5, 2007


In order to enjoy the dramatic improvements that AM IBOC has to offer, AM broadcasters must consider a system specific trade-off. AM IBOC places digital carriers up to 15 kHz on either side of an AM station’s main carrier. NRSC tests confirmed that a station transmitting an IBOC signal encounters very little, if any, interference to its own received signal. Although the IBOC digital carriers operate at very low power levels, in some cases stations on first adjacent channels may receive noticeable interference under certain listening conditions.

AM broadcasters are now offered an opportunity with IBOC to take steps that have the potential to dramatically improve the AM listening experience. Generally, interference attributable to IBOC on first adjacent channels should only be noticeable in cases where listeners are located outside the protected interference-free contour and should not cause significant AM listening problems during daytime hours. This is shown by the test results in Section 4 of this report.

No test results were obtained by the NRSC, nor were they requested from iBiquity, on skywave reception. However due to the propagation mechanisms that support skywave reception, the NRSC expects that first adjacent interference may pose potential problems for listeners during nighttime hours. Additional testing would be needed before the NRSC could further comment on the nighttime compatibility of hybrid AM IBOC. The NRSC therefore recommends that stations desiring to operate with AM IBOC do so during daytime hours only.