The rules for determining when construction of a new tower may cause a distortion of the pattern of a nearby AM station, and when the party building the new tower has a financial obligation to remedy any interference caused, were clarified by the Commission in an order released late last week. The order makes clear that all towers used by FCC licensees must abide by these rules, putting into formal rules the existing general obligation that all “newcomers” that create interference to an existing licensee must be responsible for rectifying that interference. There was apparently some question about the duty of newcomers to rectify issues that they cause to AM stations, as the rules for all non-broadcast services did not explicitly include language embodying that concept.

The Commission also made clear that the distortion of an AM stations pattern would be measured by the “moment method,” a computer program that will determine if there is a disruption to the pattern, rather than by actual field strength measurements. Doing a “proof of performance” of an AM station can be a long and costly process. Thus the FCC several years ago authorized the moment method of modeling AM patterns (see our article here). In this order, the Commission extends the reliance on this method to the resolution of complaints about new tower construction interfering with existing AM patterns. Other specifics of the order are set forth below.

The new rules, applicable to all Commission licensees in all services, broadcast and nonbroadcast, require that newcomers remedy interference to AM stations under certain procedures and parameters. Provisions of the new rules address matters including the following:

  • Short towers are generally excluded from the rules. Short towers are measured by electrical degrees, with the method of computation set forth in the rules.
  • The construction of a new tower is considered to be significant if it distorts the AM pattern by more than 2 db.
  • New towers are covered if they are within 3 km or 10 wavelengths (again as defined by the rules) of the AM tower.
  • Those constructing new towers must notify the AM station owner at least 30 days before construction is to begin so that the AM licensee can study the potential impact.
  • No notification of the permittee of an unbuilt AM station need be provided. The rules are to apply the requirement that “newcomers” protect existing users, and the FCC does not consider permittees who have not yet built their station to be an existing user.  In addition, an AM station that has not been built cannot be detuned if interference is predicted, so notification would serve no purpose.
  • Even the construction of new towers that are “short” or beyond the normal protected distance from the AM station can trigger the obligation to financially assume the responsibility to detune AM stations if the AM station can show, within two years of the new tower’s construction, that there is a disruption to the pattern of the AM station.
  • The rules only apply to towers and other structures owned by FCC licensees, except that a licensee cannot locate on a structure owned by a nonlicensee unless the tower owner does comply.
  • While the rules apply prospectively, the FCC will apply the general presumption that a newcomer must resolve problems to an existing operator to pending cases of claimed interference to an AM pattern.

These rules should help to make clear the obligation for newcomers in any communications service to assume the financial responsibility to remedy disruptions to AM stations. While the rules are complicated and must be analyzed by engineers who can determine when they apply, they should eliminate many disputes over the responsibility for the disruption of the patterns of AM radio stations.