Sec.  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 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 (a)(3) 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  Sec. 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  Sec. 15.111. The frequency range of measurements for AC power line
   conducted limits is specified in  Sec.  Sec. 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]