47 CFR § 74.751 - Modification of transmission systems.
(a) No change, either mechanical or electrical, may be made in apparatus which has been certificated by the Commission without prior authority of the Commission. If such prior authority has been given to the manufacturer of certificated equipment, the manufacturer may issue instructions for such changes citing its authority. In such cases, individual licensees are not required to secure prior Commission approval but shall notify the Commission when such changes are completed.
(b) Formal application (FCC Form 2100, Schedule C) is required for any of the following changes:
(1) Replacement of the transmitter as a whole, except replacement with a transmitter of identical power rating which has been certificated by the FCC for use by low power TV and TV translator stations, or any change which could result in a change in the electrical characteristics or performance of the station.
(2) Any change in the transmitting antenna system, including the direction of radiation, directive antenna pattern, antenna gain, transmission line loss characteristics, or height of antenna center of radiation.
(3) Any change in the overall height of the antenna structure, except where notice to the Federal Aviation Administration is specifically not required under § 17.14(b) of this chapter.
(4) Any horizontal change of the location of the antenna.
(5) A change in frequency assignment.
(6) [Reserved]
(7) A change of authorized operating power.
(c) Notwithstanding the requirements in paragraph (b) of this section, a station may file in LMS a correction of geographic coordinates where the change is 3 seconds or fewer in latitude and/or 3 seconds or fewer in longitude, provided there is no physical change in location and no other licensed parameters are changed. An exhibit should be attached to the application(s) specifying that it is a coordinate correction.
(d) Upon installation of new or replacement transmitting equipment for which prior FCC authority is not required under the provisions of this section, the licensee must place in the station records a certification that the new installation complies in all respects with the technical requirements of this part and the station authorization.