§ 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 addition of antennas to the AM tower,
   see § 1.30003.) 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;  78 FR 66298 , Nov. 5, 2013]

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