AM radio patterns are vulnerable to distortion from “reradiators” located near their transmission towers. Because of the relationship between the height of cellular wireless communication towers and the wavelength of AM signals, Federal Communications Commission (FCC) licensees are required to carry out AM reradiation protection actions when building or locating on a tower or tall facility in the vicinity of an AM station.

FCC Rules require that licensees “determine whether the [tower] construction or modification affected (or will affect) the AM station antenna pattern.” The implication is that there is concern about any effect on the pattern, and AM stations are often held to 0.5 dB tolerances in their pattern limits!

The AM radiation pattern of an AM station is authorized and licensed by the FCC after careful consideration of the location and patterns of other AM stations at or near the same frequency. The impact of a distorted pattern can negatively impact other stations far away. Distortion can reduce the market coverage area of a station, thus affecting its revenue earning capabilities. This is a particularly sensitive issue since there is so much competition in AM markets.

No. Frequently full tower detuning is not required in order to properly serve the tower operator/owner and adequately protect the AM in question. Alternative procedures can be employed that satisfy due diligence requirements for AM protection.

Through careful evaluation of the AM station’s licensed pattern, optimum locations can be determined for the placement of a communications tower—even immediately adjacent to an AM tower array. Capability even exists for installing antennas and lines directly on an AM tower! This provides a very strong advantage for licensees who are in need of an antenna site in areas that are challenged with zoning restrictions.

Yes! Technology exists that allows collocation on an otherwise “hot” AM tower.

When constructing or modifying a tower communications site in the vicinity of an AM broadcast station, the FCC licensee has the responsibility to correct disturbances to the AM station antenna pattern which may cause operation outside the radiation parameters specified by the FCC for that AM station, if the disturbance occurred as a result of the construction or modification. This requirement also includes powerlines, watertanks and other structures.

A coordinated program should be established to screen all communications sites for AM protection liability. Optimizing the placement of towers relative to AM stations is necessary. When possible, make use of AM towers as host platforms for additional antenna systems. A competent and experienced professional that provides a full range of AM protection and detuning services is your most valuable asset in meeting the FCC mandates.

Yes. The FCC mandates continued maintenance of AM detuning systems. Also check out our convenient guide to best practices in AM detuning.