§ 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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