Editing Spread spectrum (section)

=== Effect ===
Note that this method does not reduce total [[radiation|radiated]] energy, and therefore systems are not necessarily less likely to cause interference. Spreading energy over a larger bandwidth effectively reduces electrical and magnetic readings within narrow bandwidths. Typical [[measuring receiver]]s used by EMC testing laboratories divide the electromagnetic spectrum into frequency bands approximately 120&nbsp;kHz wide.<ref>American National Standard for Electromagnetic Noise and Field Strength Instrumentation, 10 Hz to 40 GHz—Specifications, ANSI C63.2-1996, Section 8.2 Overall Bandwidth</ref> If the system under test were to radiate all its energy in a narrow bandwidth, it would register a large peak. Distributing this same energy into a larger bandwidth prevents systems from putting enough energy into any one narrowband to exceed the statutory limits. The usefulness of this method as a means to reduce real-life interference problems is often debated,<ref name=IM2013/> as it is perceived that spread-spectrum clocking hides rather than resolves higher radiated energy issues by simple exploitation of loopholes in EMC legislation or certification procedures. This situation results in electronic equipment sensitive to narrow bandwidth(s) experiencing much less interference, while those with broadband sensitivity, or even operated at other higher frequencies (such as a radio receiver tuned to a different station), will experience more interference.

FCC certification testing is often completed with the spread-spectrum function enabled in order to reduce the measured emissions to within acceptable legal limits.  However, the spread-spectrum functionality may be disabled by the user in some cases. As an example, in the area of personal computers, some [[BIOS]] writers include the ability to disable spread-spectrum clock generation as a user setting, thereby defeating the object of the EMI regulations. This might be considered a [[loophole]], but is generally overlooked as long as spread-spectrum is enabled by default.