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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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282 A. L. LANCE, W. D. SEAL, AND F. LABAARA,.....---., IISIGNALIGENERATOR(FREQ.-MOD.CAPABILITY)IIIADELAY LINEHEWLETT-PACKARD5420ADIGITAL SIGNALANALYZERDUAL­CHANNELdeSCOPEDELAY LINEFIG. 24 A dual delay-line phase noise measurement system. (Courtesy Instrument Society<strong>of</strong> America.)two differential delay-line systems. The single-oscillator signal is appliedto both systems <strong>and</strong> cross-spectrum analysis is performed on the signaloutput from the two delay-line systems. Signal processing is performed withthe Hewlett-Packard 5420A digital signal analyzer. The cross spectrum isobtained by taking the product <strong>of</strong> the Fourier transform <strong>of</strong> one signal <strong>and</strong>the complex conjugate <strong>of</strong> the Fourier transform <strong>of</strong> a second signal. It isa phase-sensitive characteristic resulting in a complex product that servesas a measurement <strong>of</strong> the relative phase <strong>of</strong> two signals. Cross spectrum givesa phase- <strong>and</strong> amplitude-sensitive measurement directly. By performingthe product Sy(f) . Sx(f)*, a certain signal-to-noise enhancement is achieved.TN-233

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