B&K Precision 2552-2559 - Manual - Manual (Page 44)

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Figure 26 - Measuring FFT Frequency
NOTE： - The FFT of a waveform that has a DC component or offset
can cause incorrect FFT waveform magnitude values. To
minimize the DC component, choose AC Coupling on the
source waveform.
- To display FFT waveforms with a large dynamic range, use
the dBVrms scale. The dBVrms scale displays component
magnitudes using a log scale.
- The Nyquist frequency is the highest frequency that any
real-time digitizing oscilloscope can acquire without
aliasing. This frequency is half that of the sample rate
provided it is within the analog bandwidth of the
oscilloscope. Frequencies above the Nyquist frequency will
be undersampled, which causes aliasing.