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

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Presentation on theme: "Spectrum Analyzer CW Power Measurements and Noise 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 1."— Presentation transcript:

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

2 Overview Signal + Noise Model Bias & Variance of Noise and Signal + Noise Measurements Variance of Averaged Measurements Spectrum Analyzer Block Diagram and Measurement Recommendations 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 2

3 Signal + Noise Model 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 3

4 Noise Only Measurements 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 4 Noise voltage follows a Rayleigh distribution

5 Spectrum Analyzer Averaging Methods Averaging Types: Voltage Power Log Power 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 5

6 Noise – Measurement Bias AveragingBias (dB)Notes Power0by definition Voltage-1.05 Log Power NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 6  = Euler’s constant: …

7 Noise – Standard Deviation of Discrete Measurements AveragingStd Dev (dB)Notes Power4.34 Voltage4.54 Log Power5.77Monte Carlo 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 7

8 Signal + Noise – Measurement Bias 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 8 AveragingBias (dB) Power Voltage Log Power m = signal-to-noise ratio (W/W)  = Euler’s constant: …

9 Signal + Noise – Measurement Bias 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 9

10 Signal + Noise – Standard Deviation of Discrete Measurements 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 10 AveragingStd Dev (dB) Power Voltage Log Power m = signal-to-noise ratio (W/W)

11 Signal + Noise – Standard Deviation of Discrete Measurements 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 11

12 Standard Deviation of Averaged Measurements 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 12 Filter TypeApplicationNBW/RBW 4-pole syncMost SAs analog pole syncSome SAs analog1.111 FFT/digitalFFT/digital IF swept SAs1.056

13 Spectrum Analyzer Block Diagram 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 13

14 Spectrum Analyzer Block Diagram – Input Attenuator and Preamplifier 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 14 Attenuation = 0 dB Preamplifier On but… don’t overdrive the mixer!

15 Spectrum Analyzer Block Diagram – Preselector 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 15 set based on impact to noise floor

16 Spectrum Analyzer Block Diagram – Frequency Span & Sweep Time 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 16 span = zero sweep time = based on noise uncertainty

17 Spectrum Analyzer Block Diagram – RBW 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 17 Signal + Noise: set RBW to give at least 8 dB SNR. Reducing RBW beyond this does not give any benefit (assumes log power averaging)

18 Spectrum Analyzer Block Diagram – RBW (Signal + Noise) 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 18 SNR > 8 dB produces negligible bias when using log power averaging

19 Spectrum Analyzer Block Diagram – RBW (Signal + Noise) 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 19

20 Spectrum Analyzer Block Diagram – RBW (S+N) 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 20 For time-averaged measurements, changing RBW does not change uncertainty due to noise

21 Spectrum Analyzer Block Diagram – Envelope Detector 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 21 detector = average

22 Spectrum Analyzer Block Diagram – Video Filter 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 22 video filter = “wide open”

23 Spectrum Analyzer Block Diagram – Averaging Type 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 23 averaging type noise: power signal + noise: log power

24 Spectrum Analyzer Block Diagram – Trace Averaging & Trace Points 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 24 trace averages = 1 trace points = any function: average entire trace

25 Spectrum Analyzer Block Diagram – Summary of Recommendations FunctionNoiseSignal + Noise Input Attenuation 0 Preamplifier On Preselector based on impact to noise floor Frequency Span Zero Resolution Bandwidthwide narrow enough for SNR > 8 dB Detector average Video Bandwidth wide Averaging Type powerlog power Trace Averages 1 Trace Points n/a Function average entire trace 2012 NCSL International Workshop and Symposium Spectrum Analyzer CW Power Measurements and Noise 25


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