Guide to Spectrum and Signal Analysis

Guide to Spectrum and Signal Analysis
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Guide to Spectrum and Signal Analysis

  • www.anritsu.com | 19The spectrum analyzer display enables accurate measurement of three key AM parameters.• Modulation Factor m.• Modulation Frequency fm.• Modulation DistortionFigure 20 shows the time domain display of a typical AM signal. From this the modulation factor, m, can be expressed as follows:Since the modulation is symmetrical:Equation 4 is true for sinusoidal modulation. If we view the AM signal on a spectrum analyzer in linear (voltage) mode we obtain Figure 21.From this the percentage modulation, %M, can be calculated as follows:where Es = Amplitude of the sideband (volts) Ec = Amplitude of the carrier (volts).EcEminEmaxFigure 20Figure 21m = Emax –EcEcm = Emax –EminEmax + EminEc = Emax + Emin2Emax –Ec = Ec –Eminm = Emax –EcEcm = Emax –EminEmax + EminEc = Emax + Emin2Emax –Ec = Ec –Eminm = Emax –EcEcm = Emax –EminEmax + EminEc = Emax + Emin2Emax –Ec = Ec –Eminm = Emax –EcEcm = Emax –EminEmax + EminEc = Emax + Emin2Emax –Ec = Ec –EminEquation 1Equation 2 Equation 3Equation 4%M = x 100 (ES LSB + ES USB)EcEquation 5ES LSBES USB