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 Secs. 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 Secs. 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 Secs. 73.316 and 73.685.) 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, notification to the FCC in Washington, DC, must be filed in 
accordance with Sec. 73.54(e).

[43 1997 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]