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Spectrum Analyzer CW Power Measurements and Noise

Spectrum Analyzer CW Power Measurements and Noise. 2012 NCSL International Workshop and Symposium. Overview . Signal + Noise Model Bias & Variance of Noise and Signal + Noise Measurements Variance of Averaged Measurements Spectrum Analyzer Block Diagram and Measurement Recommendations.

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Spectrum Analyzer CW Power Measurements and Noise

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  1. Spectrum Analyzer CW Power Measurements and Noise 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise

  2. Overview Spectrum Analyzer CW Power Measurements and Noise • Signal + Noise Model • Bias & Variance of Noise and Signal + Noise Measurements • Variance of Averaged Measurements • Spectrum Analyzer Block Diagram and Measurement Recommendations

  3. Signal + Noise Model Spectrum Analyzer CW Power Measurements and Noise

  4. Spectrum Analyzer Averaging Methods Spectrum Analyzer CW Power Measurements and Noise • Averaging Types: • Voltage • Power • Log Power

  5. Noise – Measurement Bias  = Euler’s constant: 0.577216… Spectrum Analyzer CW Power Measurements and Noise

  6. Noise – Standard Deviation of Discrete Measurements Spectrum Analyzer CW Power Measurements and Noise

  7. Signal + Noise – Measurement Bias m = signal-to-noise ratio (W/W)  = Euler’s constant: 0.577216… Spectrum Analyzer CW Power Measurements and Noise

  8. Signal + Noise – Measurement Bias Spectrum Analyzer CW Power Measurements and Noise

  9. Signal + Noise – Standard Deviation of Discrete Measurements m = signal-to-noise ratio (W/W) Spectrum Analyzer CW Power Measurements and Noise

  10. Signal + Noise – Standard Deviation of Discrete Measurements Spectrum Analyzer CW Power Measurements and Noise

  11. Standard Deviation of Averaged Measurements Spectrum Analyzer CW Power Measurements and Noise • Averaging Discrete Measurements – reduced by • N = number of samples. • Time Averaged Measurements – reduced by • tint = integration (measurement) time • NBW = noise bandwidth

  12. Spectrum Analyzer Block Diagram Spectrum Analyzer CW Power Measurements and Noise

  13. Spectrum Analyzer Block Diagram – Input Attenuator and Preamplifier Attenuation = 0 dB Preamplifier On but… don’t overdrive the mixer! Spectrum Analyzer CW Power Measurements and Noise

  14. Spectrum Analyzer Block Diagram – Preselector set based on impact to noise floor Spectrum Analyzer CW Power Measurements and Noise

  15. Spectrum Analyzer Block Diagram – Frequency Span & Sweep Time span = zero sweep time = based on noise uncertainty Spectrum Analyzer CW Power Measurements and Noise

  16. Spectrum Analyzer Block Diagram – RBW Signal + Noise: set RBW to give at least 8 dB SNR. Reducing RBW beyond this does not give any benefit (assumes log power averaging) Noise: set RBW wide (power averaging) Spectrum Analyzer CW Power Measurements and Noise

  17. Spectrum Analyzer Block Diagram – RBW (Signal + Noise) SNR > 8 dB produces negligible bias when using log power averaging Spectrum Analyzer CW Power Measurements and Noise

  18. Spectrum Analyzer Block Diagram – RBW (Signal + Noise) SNR approximated by Spectrum Analyzer CW Power Measurements and Noise

  19. Spectrum Analyzer Block Diagram – RBW (S+N) For time-averaged measurements, changing RBW does not change uncertainty due to noise Spectrum Analyzer CW Power Measurements and Noise • Standard Uncertainty of discrete measurements approximated by: • m = SNR (W/W) = • For time-averaged measurements: • But • Therefore: (time-averaged, SNR > 8 dB)

  20. Spectrum Analyzer Block Diagram – Envelope Detector detector = average Spectrum Analyzer CW Power Measurements and Noise

  21. Spectrum Analyzer Block Diagram – Video Filter video filter = “wide open” Spectrum Analyzer CW Power Measurements and Noise

  22. Spectrum Analyzer Block Diagram – Averaging Type averaging type noise: power signal + noise: log power Spectrum Analyzer CW Power Measurements and Noise

  23. Spectrum Analyzer Block Diagram – Trace Averaging & Trace Points trace averages = 1 trace points = any function: average entire trace Spectrum Analyzer CW Power Measurements and Noise

  24. Spectrum Analyzer Block Diagram – Summary of Recommendations Spectrum Analyzer CW Power Measurements and Noise

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