§  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.

   [ 69 FR 69336 , Nov. 29, 2004]

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