Goto Section: 74.793 | 74.795 | Table of Contents

FCC 74.794
Revised as of January 19, 2021
Goto Year:2020 | 2022
  §  74.794   Digital emissions.

   (a)(1) An applicant for a digital LPTV or TV translator station
   construction permit shall specify that the station will be constructed
   to confine out-of-channel emissions within one of the following
   emission masks: Simple, stringent or full service.

   (2) The power level of emissions on frequencies outside the authorized
   channel of operation must be attenuated no less than following amounts
   below the average transmitted power within the authorized 6 MHz
   channel. In the mask specifications listed in § 74.794(a)(2) and (a)(3),
   A is the attenuation in dB and Δf is the frequency difference in MHz
   from the edge of the channel.

   (i) Simple mask. At the channel edges, emissions must be attenuated no
   less than 46 dB. More than 6 MHz from the channel edges, emissions must
   be attenuated no less than 71 dB. At any frequency between 0 and 6 MHz
   from the channel edges, emissions must be attenuated no less than the
   value determined by the following formula:

   A (dB) = 46 + (Δf2 /1.44)

   (ii) Stringent mask. In the first 500 kHz from the channel edges,
   emissions must be attenuated no less than 47 dB. More than 3 MHz from
   the channel edges, emissions must be attenuated no less than 76 dB. At
   any frequency between 0.5 and 3 MHz from the channel edges, emissions
   must be attenuated no less than the value determined by the following
   formula:

   A(dB) = 47 + 11.5 (Δf-0.5)

   (iii) Full service mask: (A) The power level of emissions on
   frequencies outside the authorized channel of operation must be
   attenuated no less than the following amounts below the average
   transmitted power within the authorized channel. In the first 500 kHz
   from the channel edge the emissions must be attenuated no less than 47
   dB. More than 6 MHz from the channel edge, emissions must be attenuated
   no less than 110 dB. At any frequency between 0.5 and 6 MHz from the
   channel edge, emissions must be attenuated no less than the value
   determined by the following formula:

   Attenuation in dB = −11.5([Delta]f + 3.6);

   Where:

   [Delta] f = frequency difference in MHz from the edge of the channel.

   (B) This attenuation is based on a measurement bandwidth of 500 kHz.
   Other measurement bandwidths may be used as long as appropriate
   correction factors are applied. Measurements need not be made any
   closer to the band edge than one half of the resolution bandwidth of
   the measuring instrument. Emissions include sidebands, spurious
   emissions and radio frequency harmonics. Attenuation is to be measured
   at the output terminals of the transmitter (including any filters that
   may be employed). In the event of interference caused to any service,
   greater attenuation may be required.

   (3) The attenuation values for the simple and stringent emission masks
   are based on a measurement bandwidth of 500 kHz. Other measurement
   bandwidths may be used and converted to the reference 500 kHz value by
   the following formula:

   A(dB) = Aalternate + 10 log (BWalternate / 500)

   where A(dB) is the measured or calculated attenuation value for the
   reference 500 kHz bandwidth, and Aalternate is the measured or
   calculated attenuation for a bandwidth BWalternate. Emissions include
   sidebands, spurious emissions and radio harmonics. Attenuation is to be
   measured at the output terminals of the transmitter (including any
   filters that may be employed). In the event of interference caused to
   any service by out-of-channel emissions, greater attenuation may be
   required.

   (b) In addition to meeting the emission attenuation requirements of the
   simple or stringent mask (including attenuation of radio frequency
   harmonics), digital low power TV and TV translator stations authorized
   to operate on TV channels 22-24, (518-536 MHz), 32-36 (578-608 MHz), 38
   (614-620 MHz), and 65-69 (776-806 MHz) must provide specific “out of
   band” protection to Radio Navigation Satellite Services in the bands:
   L5 (1164-1215 MHz); L2 (1215-1240 MHz) and L1 (1559-1610 MHz).

   (1) An FCC-certificated transmitter specifically certified for use on
   one or more of the above channels must include filtering with an
   attenuation of not less than 85 dB in the GPS bands, which will have
   the effect of reducing harmonics in the GPS bands from what is produced
   by the digital transmitter, and this attenuation must be demonstrated
   as part of the certification application to the Commission.

   (2) For an installation on one of the above channels with a digital
   transmitter not specifically FCC-certificated for the channel, a low
   pass filter or equivalent device rated by its manufacturer to have an
   attenuation of at least 85 dB in the GPS bands, which will have the
   effect of reducing harmonics in the GPS bands from what is produced by
   the digital transmitter, and must be installed in a manner that will
   prevent the harmonic emission content from reaching the antenna. A
   description of the low pass filter or equivalent device with the
   manufacturer's rating or a report of measurements by a qualified
   individual shall be retained with the station license. Field
   measurements of the second or third harmonic output of a transmitter so
   equipped are not required.

   [ 69 FR 69336 , Nov. 29, 2004, as amended at  76 FR 44828 , July 27, 2011]

   


Goto Section: 74.793 | 74.795

Goto Year: 2020 | 2022
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