§  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 § § 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 § § 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
   § 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
   § 73.51(a)(1) or (d). (If the changes are due to the construction of FM
   or TV transmitting facilities, see § § 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 § 73.54. Operating power should then be
   determined by a direct method as described in § 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 § 73.54(d).

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