Agilent Technologies 93000 SOC Series Training Manual page 562

Appendix A
Characteristics of the Frequency Domain
In frequency domain, we can see the purity of a signal.
Harmonics Appear in the Spectrum
Signals that seem perfect in time domain, may show major
distortions (additional components) in frequency domain.
Purpose of Frequency Domain Measurements
In general, we use the frequency domain to measure the 'purity' of
a signal, that is, to see whether there are additional frequency
components besides the dominant frequency.
In the frequency domain, such small components are easy to see,
because they are not masked by larger ones. Once they are
separated, they can be measured.
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