FFT Spectral Analysis 4
Keysight InfiniiVision HD3-Series Oscilloscopes User's Guide 73
Aliasing happens when there are frequency components in the signal higher than
half the sample rate. Because the FFT spectrum is limited by this frequency, any
higher components are displayed at a lower (aliased) frequency.
Because the frequency span goes from ≈ 0 to the Nyquist frequency, the best way
to prevent aliasing is to make sure that the frequency span is greater than the
frequencies of significant energy present in the input signal.
FFT Spectral Leakage
The FFT operation assumes that the time record repeats. Unless there is an
integral number of cycles of the sampled waveform in the record, a discontinuity is
created at the end of the record. This is referred to as leakage. In order to minimize
spectral leakage, windows that approach zero smoothly at the beginning and end
of the signal are employed as filters to the FFT. The FFT Menu provides these
windows: Hanning, Flat Top, Rectangular, Blackman-Harris, and Bartlett.
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