§ 1.30002   Tower construction or modification near AM stations.

   (a) Proponents of construction or significant modification of a tower which
   is within one wavelength of a nondirectional AM station, and is taller than
   60 electrical degrees at the AM frequency, must notify the AM station at
   least 30 days in advance of the commencement of construction. The proponent
   shall examine the potential impact of the construction or modification as
   described  in  paragraph  (c)  of this section. If the construction or
   modification would distort the radiation pattern by more than 2 dB, the
   proponent shall be responsible for the installation and maintenance of any
   detuning  apparatus  necessary  to  restore  proper  operation  of the
   nondirectional antenna.

   (b) Proponents of construction or significant modification of a tower which
   is within the lesser of 10 wavelengths or 3 kilometers of a directional AM
   station, and is taller than 36 electrical degrees at the AM frequency, must
   notify the AM station at least 30 days in advance of the commencement of
   construction.  The proponent shall examine the potential impact of the
   construction or modification as described in paragraph (c) of this section.
   If the construction or modification would result in radiation in excess of
   the AM station's licensed standard pattern or augmented standard pattern
   values,  the  proponent  shall be responsible for the installation and
   maintenance of any detuning apparatus necessary to restore proper operation
   of the directional antenna.

   (c) Proponents of construction or significant modification of a tower within
   the distances defined in paragraphs (a) and (b) of this section of an AM
   station shall examine the potential effects thereof using a moment method
   analysis. The moment method analysis shall consist of a model of the AM
   antenna  together  with the potential re-radiating tower in a lossless
   environment. The model shall employ the methodology specified in § 73.151(c)
   of this chapter, except that the AM antenna elements may be modeled as a
   series of thin wires driven to produce the required radiation pattern,
   without any requirement for measurement of tower impedances.

   (d) A significant modification of a tower in the immediate vicinity of an AM
   station is defined as follows:

   (1) Any change that would alter the tower's physical height by 5 electrical
   degrees or more at the AM frequency; or

   (2) The addition or replacement of one or more antennas or transmission
   lines on a tower that has been detuned or base-insulated.

   (e)  The  addition or modification of an antenna or antenna-supporting
   structure on a building shall be considered a construction or modification
   subject to the analysis and notice requirements of this subpart if and only
   if  the  height  of the antenna-supporting structure alone exceeds the
   thresholds in paragraphs (a) and (b) of this section.

   (f)  With  respect  to an AM station that was authorized pursuant to a
   directional proof of performance based on field strength measurements, the
   proponent of the tower construction or modification may, in lieu of the
   study  described in paragraph (c) of this section, demonstrate through
   measurements taken before and after construction that field strength values
   at the monitoring points do not exceed the licensed values. In the event
   that  the pre-construction monitoring point values exceed the licensed
   values, the proponent may demonstrate that post-construction monitoring
   point values do not exceed the pre-construction values. Alternatively, the
   AM station may file for authority to increase the relevant monitoring-point
   value after performing a partial proof of performance in accordance with
   § 73.154 to establish that the licensed radiation limit on the applicable
   radial is not exceeded.

   (g) Tower construction or modification that falls outside the criteria
   described in the preceding paragraphs is presumed to have no significant
   effect on an AM station. In some instances, however, an AM station may be
   affected by tower construction or modification notwithstanding the criteria
   set forth above. In such cases, an AM station may submit a showing that its
   operation has been affected by tower construction or modification. Such a
   showing shall consist of either a moment method analysis as described in
   paragraph  (c) of this section, or of field strength measurements. The
   showing shall be provided to:

   (1) The tower proponent if the showing relates to a tower that has not yet
   been constructed or modified and otherwise to the current tower owner; and

   (2) To the Commission, within two years after the date of completion of the
   tower construction or modification. If necessary, the Commission shall
   direct the tower proponent or tower owner, if the tower proponent or tower
   owner holds a Commission authorization, to install and maintain any detuning
   apparatus  necessary to restore proper operation of the AM antenna. An
   applicant  for a Commission authorization may not propose, and a party
   holding a Commission authorization may not locate, an antenna on any tower
   or support structure that has been shown to affect an AM station's operation
   pursuant to this subparagraph, or for which a disputed showing of effect on
   an AM station's operation is pending, unless the applicant, party, or tower
   owner notifies the AM station and takes appropriate action to correct the
   disturbance to the AM pattern.

   (h) An AM station may submit a showing that its operation has been affected
   by tower construction or modification that was commenced or completed prior
   to or on the effective date of the rules adopted in this Part pursuant to MM
   Docket No. 93-177. Such a showing shall consist of either a moment method
   analysis as described in paragraph (c) of this section, or of field strength
   measurements. The showing shall be provided to the current tower owner and
   the Commission within one year of the effective date of the rules adopted in
   this Part pursuant to MM Docket No. 93-177. If necessary, the Commission
   shall  direct  the  tower owner, if the tower owner holds a Commission
   authorization, to install and maintain any detuning apparatus necessary to
   restore proper operation of the AM antenna.

   (i) An applicant for a Commission authorization may not propose, and a party
   holding a Commission authorization may not locate, an antenna on any tower
   or support structure, whether constructed before or after December 5, 2013,
   that meets the criteria in paragraphs (a) and (b) of this section, unless
   the analysis and notice process described in this subpart, and any necessary
   measures to correct disturbances of the AM radiation pattern, have been
   completed by the tower owner, the party proposing to locate the antenna, or
   any other party, either prior to construction or at any other time prior to
   the proposal or antenna location.

   [ 78 FR 66295 , Nov. 5, 2013]

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