Digital Storage Oscilloscope 18
Applying a window to the YT waveform changes the waveform so that the start and
stop values are close to each other, which reduces the discontinuities.
The Math FFT function has three FFT Window options. There is a trade-off between
frequency resolution and amplitude accuracy for each type of window. You shall
determine which one to choose according to the object you want to measure and the
source signal characteristics.
Better frequency, poorer amplitude accuracy than
Flattop
Better amplitude, poorer frequency accuracy
than Hanning
Pulse or
Transient
Waveform
Special-purpose window applicable to
discontinuous waveforms. This is actually the
same as no windows.
Best
magnitude,worst
frequency
resolution
Single frequency waveforms, to Find higher order
harmonics.
2.7.2.4 FFT Aliasing
Problems occur when the time-domain waveform acquired by the oscilloscope contains
frequency components higher than the Nyquist frequency. The frequency components
above the Nyquist frequency will be undersampled and displayed as lower frequency
components that ‘fold back’ from the Nyquist frequency. These erroneous components
are called aliases.
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