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Spectrum Analyzer Measurements and Noise Application Note 1303 Measuring Noise and Noise-like Digital Communications Signals with a Spectrum Analyzer 2 Table of contents Part I: Noise measurements ...3 Introduction ...3 Simple noise--Baseband, Real, Gaussian...3 Bandpassed noise--I and Q ...3 Measuring the power of noise with an envelope detector ...6 Logarithmic processing ...7 Measuring the power of noise with a log-envelope scale...8 Equivalent noise bandwidth ...8 The noise marker...9 Spectrum analyzers and envelope detectors ...10 Cautions when measuring noise with spectrum analyzers...12 Part II: Measurements of noise-like signals ...14 The noise-like nature of digital signals ...14 Channel-power measurements ...14 Adjacent-Channel Power (ACP)...16 Carrier power...16 Peak-detected noise (and TDMA ACP measurements) ...18 Part III: Averaging and the noisiness of noise measurements ...19 Variance and averaging...19 Averaging a number of computed results...20 Swept versus FFT analysis ...20 Zero span...20 The standard deviation of measurement noise...21 Examples...