Spectrum Analyzer Measurements 3-21 AM/FM Modulation Measurement (Option 509)
Spectrum Analyzer MG PN: 10580-00447 Rev. H 3-109
Total harmonic distortion (THD) measurement extracts the total harmonic distortion component from the
noise component in the total unwanted signal. The isolated distortion component is useful to troubleshoot the
root causes of the modulation distortion.
Where, V
n
= RMS value of the nth harmonic voltage, n = 10, V
1
= RMS value of the fundamental component.
Note
Total harmonic distortion is calculated based on maximum of 10 harmonics. For the selected AM/FM
modulation mode, the frequency of harmonics beyond the bandwidth of the audio signal is not
measured.
THD
V
2
2
V
2
3
V
2
4
V
2
n
++++
V
1
------------------------------------------------------------------------
=
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