§ 74.796 - Modification of digital transmission systems and analog transmission systems for digital operation.
(a) The provisions of § 74.751 shall apply to the modification of digital low power TV and TV translator transmission systems and the modification of existing analog transmission systems for digital operation.
(b) The following additional provisions shall apply to the modification of existing analog transmissions systems for digital operation, including installation of manufacturers' certificated equipment (“field modification kits”) and custom modifications.
(1) The modifications and related performance-testing shall be undertaken by a person or persons qualified to perform such work.
(2) The final amplifier stage of an analog transmitter modified for digital operation shall not have an “average digital power” output greater than 25 percent of its previous NTSC peak sync power output, unless the amplifier has been specifically refitted or replaced to operate at a higher power.
(3) Analog heterodyne translators, when modified for digital operation, will produce a power output (digital average power over the 6 MHz channel) not exceeding 30 watts for transmitters operating on channels 14-69 and 3 watts for transmitters operating on channels 2-13.
(4) After completion of the modification, suitable tests and measurements shall be made to demonstrate compliance with the applicable requirements in this section including those in § 74.795. Upon installation of a field modification kit, the transmitter shall be performance-tested in accordance with the manufacturer's instructions.
(5) The station licensee shall notify the Commission upon completion of the transmitter modifications. In the case of custom modifications (those not related to installation of manufacturer-supplied and FCC-certificated equipment), the licensee shall certify compliance with all applicable transmission system requirements.
(6) The licensee shall maintain with the station's records for a period of not less than two years the following information and make this information to the Commission upon request:
(i) A description of the modifications performed and performance tests or, in the case of installation of a manufacturer-supplied modification kit, a description of the nature of the modifications, installation and test instructions and other material provided by the manufacturer;
(ii) Results of performance-tests and measurements on the modified transmitter; and
(iii) Copies of related correspondence with the Commission.
(c) In connection with the on-channel conversion of existing analog transmitters for digital operation, a limited allowance is made for transmitters with final amplifiers that do not meet the attenuation of the Simple emission mask at the channel edges. Station licensees may obtain equivalent compliance with this attenuation requirement in the following manner:
(1) Measure the level of attenuation of emissions below the average digital power output at the channel edges in a 500 kHz bandwidth; measurements made over a different measurement bandwidth should be corrected to the equivalent attenuation level for a 500 kHz bandwidth using the formula given in § 74.794;
(2) Calculate the difference in dB between the 46 dB channel-edge attenuation requirement of the Simple mask;
(3) Subtract the value determined in the previous step from the authorized effective radiated power (“ERP”) of the analog station being converted to digital operation. Then subtract an additional 6 dB to account for the approximate difference between analog peak and digital average power. For this purpose, the ERP must be expressed in decibels above one kilowatt: ERP(dBk) = 10 log ERP(kW);
(4) Convert the ERP calculated in the previous step to units of kilowatts; and
(5) The ERP value determined through the above procedure will produce equivalent compliance with the attenuation requirement of the simple emission mask at the channel edges and should be specified as the digital ERP in the minor change application for an on-channel digital conversion. The transmitter may not be operated to produce a higher digital ERP than this value.