Fig. 30
Hanning window
22.2. Quick Tips
*
If desired, use the zoom feature to magnify the FFT waveform.
*
Use the default dBV RMS scale to see a detailed view of multiple frequencies, even if they have very
different amplitudes. Use the linear RMS scale to see an overall view of how all frequencies compare to
each other.
*
Signals that have a DC component or offset can cause incorrect FFT waveform component magnitude
values. To minimize the DC component, choose AC Coupling on the source signal.
*
To reduce random noise and aliased components in repetitive or single-shot events, set the oscilloscope
acquisition mode to average.
22.3. Term interpretation
Nyquist frequency:
The highest frequency that any Real Time Digital Oscilloscope can measure is exactly
half of the sampling rate under the condition of no mistakes, which is called Nyquist
frequency. If under-sampling occurs when the frequency sampled is higher than Nyquist
frequency, “False Wave” phenomenon will appear. So pay more attention to the relation
between the frequency being sampled and measured.
NOTE:
In FFT mode, the following settings are prohibited:
1.
Window set;
2.
change source channel (in CH1 Setup or CH2 Setup menu);
3.
XY Format in DISPLAY SET;
4.
“SET 50%” (the triggering level at the vertical point of signal amplitude) in Trigger setting;
5.
Autoscale.
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