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New FCC regulations on disturbance of AM patterns

A large change in the regulations of towers near AM stations has taken place. The FCC has released new rules on Disturbance of AM broadcast station antenna patterns. These are in 47 CFR Part 1, Subpart BB, 1.30000 through 1.30004 and released as FCC 13-115. These rules went into effect on February 20, 2014. See our white paper AM Disturbance Rule Change for more information.

What are AM Detuning Services?

AM detuning box AM Detuning Services include the assessment and correction of pattern distortion where wireless antenna structures (i.e., towers) can unintentionally interfere with an AM broadcast station's antenna pattern. While wireless signals do not interfere with an AM station's broadcast pattern, towers can cause AM broadcast pattern disturbances. Depending on the proximity to an AM station and the height of the proposed new structure, the structure can intercept a substantial amount of energy from a nearby AM station, re-radiate it, and scatter it in other directions producing unwanted changes in the shape of the AM station's FCC-licensed coverage area.

Regulatory Requirement

The FCC Rules 47 CFR Part 1, Subpart BB, 1.30000 through 1.30004 mandates that any FCC permittee or licensee holder that constructs or modifies towers in the immediate vicinity of an AM broadcast station is responsible for measures necessary to correct disturbances to the AM station's antenna pattern. The actions include:

  • AM station notification of the action with required 30 day reply and comment period by the AM station (after receipt of the notification)
  • An analysis of potential AM pattern interference through a Method of Moments (MoM) computer modeling that includes the AM station and the tower in the case of new build sites or existing towers undergoing significant modification (height change).
  • Detuning of the structure if indicated by the analysis or inspection and adjustment of existing detuning equipment if the structure is already so equipped.
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