47 CFR § 73.1675 - Auxiliary antennas.
(1) An auxiliary antenna is one that is permanently installed and available for use when the main antenna is out of service for repairs or replacement. An auxiliary antenna may be located at the same transmitter site as the station's main antenna or at a separate site. The service contour of the auxiliary antenna may not extend beyond the following corresponding contour for the main facility:
(i) AM stations: The 0.5 mV/m field strength contours.
(ii) FM stations: The 1.0 mV/m field strength contours.
(iii) TV stations: The Grade B coverage contours.
(iv) Class A TV stations: The protected contours defined in § 73.6010.
(2) An application for an auxiliary antenna for an AM station filed pursuant to paragraphs (b) or (c) of this section must contain a map showing the 0.5 mV/m field strength contours of both the main and auxiliary facilities.
(b) An application for a construction permit to install a new auxiliary antenna, or to make changes in an existing auxiliary antenna for which prior FCC authorization is required (see § 73.1690), must be filed on FCC Form 301 (FCC Form 340 for noncommercial educational stations).
(1) Where an FM, TV or Class A TV licensee proposes to use a formerly licensed main facility as an auxiliary facility, or proposes to modify a presently authorized auxiliary facility, and no changes in the height of the antenna radiation center are required in excess of the limits in § 73.1690(c)(1), the FM, TV or Class A TV licensee may apply for the proposed auxiliary facility by filing a modification of license application. The modified auxiliary facility must operate on the same channel as the licensed main facility. An exhibit must be provided with this license application to demonstrate compliance with § 73.1675(a). All FM, TV and Class A TV licensees may request a decrease from the authorized facility's ERP in the license application. An FM, TV or Class A TV licensee may also increase the ERP of the auxiliary facility in a license modification application, provided the application contains an analysis demonstrating compliance with the Commission's radiofrequency radiation guidelines, and an analysis showing that the auxiliary facility will comply with § 73.1675(a). Where an FM, TV, or Class A TV licensee or permittee proposes to mount an auxiliary facility on an AM tower, it must also demonstrate compliance with § 1.30003 in the license application.
(2) Where an AM licensee proposes to use a former licensed main facility as an auxiliary facility with an ERP less than or equal to the ERP specified on the former main license, the AM station may apply to license the proposed auxiliary facility by filing a modification of license application on Form 302-AM. The proposed auxiliary facilities must have been previously licensed on the same frequency as the present main facility. The license application must contain an exhibit to demonstrate compliance with § 73.1675(a).