Sec. 73.685  Transmitter location and antenna system.

                                * * * * *

    (h) Where simultaneous use of antennas or antenna structures is 
proposed, the following provisions shall apply:
    (1) In cases where it is proposed to use a tower of an AM broadcast 
station as a supporting structure for a television broadcast antenna, an 
appropriate application for changes in the radiating system of the AM 
broadcast station must be filed by the licensee thereof. A formal 
application (FCC Form 301, or FCC Form 340 for a noncommercial 
educational station) will be required if the proposal involves 
substantial change in the physical height or radiation characteristics 
of the AM broadcast antennas; otherwise an informal application will be 
acceptable. (In case of doubt, an informal application (letter) together 
with complete engineering data should be submitted.) An application may 
be required for other classes of stations when the tower is to be used 
in connection with a television station.
    (2) When the proposed TV antenna is to be mounted on a tower in the 
vicinity of an AM station directional antenna system and it appears that 
the operation of the directional antenna system may be affected, an 
engineering study must be filed with the TV application concerning the 
effect of the TV antenna on the AM directional radiation pattern. Field 
measurements of the AM stations may be required prior to and following 
construction of the TV station antenna, and readjustments made as 
necessary.