§  15.33   Frequency range of radiated measurements.

   (a) For an intentional radiator, the spectrum shall be investigated
   from the lowest radio frequency signal generated in the device, without
   going below 9 kHz, up to at least the frequency shown in this
   paragraph:

   (1) If the intentional radiator operates below 10 GHz: to the tenth
   harmonic of the highest fundamental frequency or to 40 GHz, whichever
   is lower.

   (2) If the intentional radiator operates at or above 10 GHz and below
   30 GHz: to the fifth harmonic of the highest fundamental frequency or
   to 100 GHz, whichever is lower.

   (3) If the intentional radiator operates at or above 30 GHz: to the
   fifth harmonic of the highest fundamental frequency or to 200 GHz,
   whichever is lower, unless specified otherwise elsewhere in the rules.

   (4) If the intentional radiator operates at or above 95 GHz: To the
   third harmonic of the highest fundamental frequency or to 750 GHz,
   whichever is lower, unless specified otherwise elsewhere in the rules.

   (5) If the intentional radiator contains a digital device, regardless
   of whether this digital device controls the functions of the
   intentional radiator or the digital device is used for additional
   control or function purposes other than to enable the operation of the
   intentional radiator, the frequency range shall be investigated up to
   the range specified in paragraphs (a)(1) through (4) of this section or
   the range applicable to the digital device, as shown in paragraph
   (b)(1) of this section, whichever is the higher frequency range of
   investigation.

   (b) For unintentional radiators:

   (1) Except as otherwise indicated in paragraphs (b)(2) or (b)(3) of
   this section, for an unintentional radiator, including a digital
   device, the spectrum shall be investigated from the lowest radio
   frequency signal generated or used in the device, without going below
   the lowest frequency for which a radiated emission limit is specified,
   up to the frequency shown in the following table:
   Highest frequency generated or used in the device or on which the
   device operates or tunes (MHz) Upper frequency of measurement range
   (MHz)
   Below 1.705 30.
   1.705-108 1000.
   108-500 2000.
   500-1000 5000.
   Above 1000 5th harmonic of the highest frequency or 40 GHz, whichever
   is lower.

   (2) A unintentional radiator, excluding a digital device, in which the
   highest frequency generated in the device, the highest frequency used
   in the device and the highest frequency on which the device operates or
   tunes are less than 30 MHz and which, in accordance with § 15.109, is
   required to comply with standards on the level of radiated emissions
   within the frequency range 9 kHz to 30 MHz, such as a CB receiver or a
   device designed to conduct its radio frequency emissions via connecting
   wires or cables, e.g., a carrier current system not intended to
   radiate, shall be investigated from the lowest radio frequency
   generated or used in the device, without going below 9 kHz (25 MHz for
   CB receivers), up to the frequency shown in the following table. If the
   unintentional radiator contains a digital device, the upper frequency
   to be investigated shall be that shown in the table below or in the
   table in paragraph (b)(1) of this section, as based on both the highest
   frequency generated and the highest frequency used in the digital
   device, whichever range is higher.
   Highest frequency generated or used in the device or on which the
   device operates or tunes (MHz) Upper frequency of measurement range
   (MHz)
   Below 1.705 30
   1.705-10 400
   10-30 500

   (3) Except for a CB receiver, a receiver employing superheterodyne
   techniques shall be investigated from 30 MHz up to at least the second
   harmonic of the highest local oscillator frequency generated in the
   device. If such receiver is controlled by a digital device, the
   frequency range shall be investigated up to the higher of the second
   harmonic of the highest local oscillator frequency generated in the
   device or the upper frequency of the measurement range specified for
   the digital device in paragraph (b)(1) of this section.

   (c) The above specified frequency ranges of measurements apply to the
   measurement of radiated emissions and, in the case of receivers, the
   measurement to demonstrate compliance with the antenna conduction
   limits specified in § 15.111. The frequency range of measurements for AC
   power line conducted limits is specified in § § 15.107 and 15.207 and
   applies to all equipment subject to those regulations. In some cases,
   depending on the frequency(ies) generated and used by the equipment,
   only signals conducted onto the AC power lines are required to be
   measured.

   (d) Particular attention should be paid to harmonics and subharmonics
   of the fundamental frequency as well as to those frequencies removed
   from the fundamental by multiples of the oscillator frequency.
   Radiation at the frequencies of multiplier states should also be
   checked.

   [ 54 FR 17714 , Apr. 25, 1989, as amended at  61 FR 14502 , Apr. 2, 1996;
    63 FR 42278 , Aug. 7, 1998;  84 FR 25691 , June 4, 2019]