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NIST Technical Note 1337: Characterization of Clocks and Oscillators

NIST Technical Note 1337: Characterization of Clocks and Oscillators

NIST Technical Note 1337: Characterization of Clocks and Oscillators

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12 FREQUENCY AND TIME MEASUREMENT19512.1.1 Relationship between the Power Spectrum <strong>and</strong> thePhase SpectrumThe power spectrum differs from a delta function b(j) due to the presence<strong>of</strong> the amplitude- <strong>and</strong> phase-noise terms, c(c) <strong>and</strong> ¢(t), respectively, includedin Eq. (12-1). Usually the noise modulation separates into two distinctcomponents, so that one observes a very narrow feature called the carrierabove the level <strong>of</strong> a relatively broad pedestal. The frequency that separatesthe carrier <strong>and</strong> pedestal is denoted fe' Below this frequency the spectraldensity <strong>of</strong> the carrier exceeds that <strong>of</strong> the pedestal. Assuming that the amplitudenoise is negligible compared to the phase noise <strong>and</strong> that the phasemodulation is small, the relationship between the power <strong>and</strong> phase spectrais given by (Walls <strong>and</strong> DeMarchi, 1975)STS(j) ~ VJ e-1(fcl x {J(f), if -fc

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