Section 73.1590 - Equipment performance measurements(a) The licensee of each AM, FM, TV and Class A TV station, except licensees of Class D non-commercial educational FM stations authorized to operate with 10 watts or less output power, must make equipment performance measurements for each main transmitter as follows:(1) Upon initial installation of a new or replacement main transmitter.(2) Upon modification of an existing transmitter made under the provisions of § 73.1690 , Modification of transmission systems, and specified therein.(3) Installation of AM stereophonic transmission equipment pursuant to § 73.128 .(4) Installation of FM subcarrier or stereophonic transmission equipment pursuant to § 73.295 , § 73.297 , § 73.593 or § 73.597 .(6) Annually, for AM stations, with not more than 14 months between measurements.(7) When required by other provisions of the rules or the station license.(b) Measurements for spurious and harmonic emissions must be made to show compliance with the transmission system requirements of § 73.44 for AM stations; § 73.317 for FM stations and § 73.687 for TV stations. Measurements must be made under all conditions of modulation expected to be encountered by the station whether transmitting monophonic or stereophonic programs and providing subsidiary communications services.(c) TV visual equipment performance measurements must be made with the equipment adjusted for normal program operation at the transmitter antenna sampling port to yield the following information:(2) Data showing that the waveform of the transmitted signal conforms to that specified by the standards for TV transmissions.(4) Data showing envelope delay characteristics of the radiated signal.(5) Data showing the attenuation of spurious and harmonic radiation, if, after type acceptance, any changes have been made in the transmitter or associated equipment (filters, multiplexer, etc.) which could cause changes in its radiation products.(d) The data required by paragraphs (b) and (c) of this section, together with a description of the equipment and procedure used in making the measurements, signed and dated by the qualified person(s) making the measurements, must be kept on file at the transmitter or remote control point for a period of 2 years, and on request must be made available during that time to duly authorized representatives of the FCC.47 FR 8589, Mar. 1, 1982, as amended at 51 FR 18450, May 20, 1986; 65 FR 30004 , May 10, 2000