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Publication Number: 252845 Rule Parts:  Publication Date: 01/08/2008
Keyword: Spread Spectrum Computer Clocks

First Category: Radio Service Rules
Second Category: Part 15 General

Is it acceptable to use a Spread Spectrum Oscillator for a Part 15b computer product to reduce measurable energy levels?

Answer:     It is permissible to use a Spread Spectrum Clock Generator (SSCG) for a digital device.  When measuring the emissions from a digital device with a SSCG,  the sweep of the clock frequency as stated in Section 15.31 ( c )  does not have to be stopped.  SSCG devices do not sweep, but frequency modulate within a narrow frequency range similar to the inherent jitter of non-SSCG clock generators.  Since a SSCG cannot stop the sweep at a frequency, it cannot be measured in this manner because it will not operate.  Allow the clock to run normally while performing CISPR Quasi-Peak Measurements just like any other digital device.


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