AM Plus FM (Incidental FM) of Spectrum Analyzer

Chapter AM Plus FM (Incidental FM)

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

  • 32 | Guide to Spectrum and Signal AnalysisAM Plus FM (Incidental FM)Although AM and FM are different methods of modulation, they have one property in common; they always produce a symmetrical sideband spectrum.Figure 37 illustrates a modulated carrier with asymmetrical sidebands. One way this could occur is if both AM and FM or AM and phase modulation exist simultaneously at the same modulating frequency. This indicates that the phase relationship between carrier and sidebands are different for the AM and the angular modulation. Since the sideband components of both modulation types add together vectorally, the resultant amplitude of one sideband may be reduced while the amplitude of the other would be increased accordingly. The spectrum analyzer does not retain any phase information and so in each case displays the absolute magnitude of the result.Figure 37