47 CFR § 73.62 - Directional antenna system operation and tolerances.
(a) Each AM station operating a directional antenna must maintain the relative amplitudes of the antenna currents, as indicated by the antenna monitor, within 5% of the values specified on the instrument of authorization. Directional antenna relative phases must be maintained within 3 degrees of the values specified on the instrument of authorization.
(b) In the event of a failure of system components, improper pattern switching or any other event that results in operation substantially at variance from the radiation pattern specified in the instrument of authorization for the pertinent time of day, operation must be terminated within three minutes unless power can be reduced sufficiently to eliminate any excessive radiation. See § 73.1350(e).
(1) Any variation of operating parameters by more than ±15 percent sample current ratio or ±10 degrees in phase, any monitor point that exceeds 125 percent of the licensed limit, or any operation at variance that results in complaints of interference shall be considered operation substantially at variance from the license and will require immediate corrective action.
(c) In the event of minor variations of directional antenna operating parameters from the tolerances specified in paragraph (a) of this section, the following procedures will apply:
(1) The licensee shall measure and log every monitoring point at least once for each mode of directional operation. Subsequent variations in operating parameters will require the remeasuring and logging of every monitoring point to assure that the authorized monitoring point limits are not being exceeded. The licensee will be permitted 24 hours to accomplish these actions; provided that, the date and time of the failure to maintain proper operating parameters have been recorded in the station log.
(2) Provided each monitoring point is within its specified limit, operation may continue for a period up to 30 days before a request for Special Temporary Authority (STA) must be filed, pursuant to paragraph (c)(4) of this section, to operate with parameters at variance from the provisions of paragraph (a) of this section.
(3) If any monitoring point exceeds its specified limit, the licensee must either terminate operation within three hours or reduce power in accordance with the applicable provisions of § 73.1350(d), in order to eliminate any possibility of interference or excessive radiation in any direction.
(4) If operation pursuant to paragraph (c)(3) of this section is necessary, or before the 30-day period specified in paragraph (c)(2) of this § expires, the licensee must request a Special Temporary Authority (STA) in accordance with section 73.1635 to continue operation with parameters at variance and/or with reduced power along with a statement certifying that all monitoring points will be continuously maintained within their specified limits.
(d) In any other situation in which it might reasonably be anticipated that the operating parameters might vary out of tolerance (such as planned array repairs or adjustment and proofing procedures), the licensee shall, before such activity is undertaken, obtain a Special Temporary Authority (STA) in accordance with § 73.1635 in order to operate with parameters at variance and/or with reduced power as required to maintain all monitoring points within their specified limits.