§ 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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