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Tag Archives: AM Detuning

FCC Revamps AM Detuning Rules

The FCC’s broadcast rules contained several sections dealing with tower placement near AM antennas to protect AM stations from the potential effects of nearby tower construction. However, two prominent rule sections dealing with wireless communications, namely Part 90 (Land Mobile Radio) and Part 24 (Personal Communications Services) entirely lack provisions for protecting AM stations from the possible effects of nearby tower construction.

By its recent Order in MM Docket No. 93-177 (Rel. Aug. 16, 2013), the FCC seeks to harmonize and streamline its rules by establishing a single protection scheme for tower construction and modification near AM tower arrays, and by designating “moment method” modeling as the principal means of determining whether a nearby tower affects an AM station radiation pattern.

The prior rules required licensees and permittees to notify AM stations and take appropriate action when a tower was constructed within a fixed distance of an AM station. This fixed distance approach has now been replaced by one that defines the critical distance from AM stations based on the incumbent’s frequency and the proponent’s tower height. The critical distance for a non-directional AM station is one wavelength at the frequency of the AM station. The critical distance for a directional AM station is 10 wavelengths of the frequency of the AM station up to a maximum distance of three kilometers.

The new rules exempt short towers from the AM proximity analysis requirement because such low-in-stature towers are inefficient radiators that would not generally affect an AM broadcast pattern. The threshold height for new tower erections or major modifications to comply with the requisite AM proximity analysis is 36 electrical degrees for a directional antenna array, and 60 electrical degrees for a non-directional antenna. Three hundred sixty electrical degrees equals one wavelength at the frequency of the AM transmitter.

By this Order, the FCC has harmonized and streamlined the rules regarding tower construction and modification near AM stations, improved the protections afforded AM broadcasters, and reduced the time required to determine the effect of tower construction in the vicinity of AM stations while reducing the costs of such analysis. The adoption of the new rules goes a long way toward mitigating any confusion among affected parties while ensuring consistent protection of AM station operations and providing greater cost certainty for tower owners.

For more information, see the FCC’s Report and Order.

Michael L. Higgs Jr., member of the Shulman Rogers telecom practice, assisted with the reporting.