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Section 15.33 Frequency range of radiated measurements.
(a) Unless otherwise noted in the specific rule section under which the equipment
operates 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)-(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), 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 Section 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) above, 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 Section 15.111. The frequency
range of measurements for AC power line conducted limits is specified in Sections 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 stages
should also be checked.
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