Sec.  73.45   AM antenna systems.

   (a) All applicants for new, additional, or different AM station facilities
   and all licensees requesting authority to change the transmitting system
   site of an existing station must specify an antenna system, the efficiency
   of which complies with the requirements for the class and power of station.
   (See  Sec.  Sec. 73.186 and 73.189.)

   (1) An application for authority to install an AM broadcast antenna must
   specify a definite site and include full details of the antenna system
   design and expected performance.

   (2) All data necessary to show compliance with the terms and conditions of
   the construction permit must be filed with the application for the station
   license to cover the construction. If the station has constructed a
   directional antenna, a directional proof of performance must be filed. See
    Sec.  Sec. 73.150 through 73.157.

   (b) The simultaneous use of a common antenna or antenna structure by more
   than one AM station or by a station of any other type or service may be
   authorized provided:

   (1) Engineering data are submitted showing that satisfactory operation of
   each station will be obtained without adversely affecting the operation of
   the other station(s).

   (2) The minimum field strength for each AM station complies with  Sec. 73.189(b).

   (c) Should any changes be made or otherwise occur which would possibly alter
   the resistance of the antenna system, the licensee must commence the
   determination of the operating power by a method described in  Sec. 73.51(a)(1)
   or (d). (If the changes are due to the construction of FM or TV transmitting
   facilities, see  Sec.  Sec. 73.316, 73.685, and 73.1692.) Upon completion of any
   necessary repairs or adjustments, or upon completion of authorized
   construction or modifications, the licensee must make a new determination of
   the antenna resistance using the procedures described in  Sec. 73.54. Operating
   power should then be determined by a direct method as described in  Sec. 73.51.
   Notification of the value of resistance of the antenna system must be filed
   with the FCC in Washington, DC as follows:

   (1) Whenever the measurements show that the antenna or common point
   resistance differs from that shown on the station authorization by more than
   2%, FCC Form 302 must be filed with the information and measurement data
   specified in  Sec. 73.54(d).

   (2) Whenever AM stations use direct reading power meters pursuant to  Sec. 73.51,
   a letter notification to the FCC in Washington, DC, Attention: Audio
   Division, Media Bureau, must be filed in accordance with  Sec. 73.54(e).

   [ 43 FR 53735 , Nov. 17, 1978, as amended at  45 FR 28141 , Apr. 28, 1980;  47 FR 8589 , Mar. 1, 1982;  50 FR 32416 , Aug. 12, 1985;  51 FR 2707 ; Jan. 21, 1986;
    51 FR 26250 , July 22, 1986;  63 FR 33875 , June 22, 1998;  67 FR 13231 , Mar.
   21, 2002]