Iwatsu DS-8814, Operation Manual

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F-16
Similarly, when performing an FFT, data containing frequency components higher than
1/2 the sampling rate (Nyquist frequency), aliasing will occur and the waveform will
appear to have a lower frequency.
With this product, the FFT sampling rate is displayed at the bottom of the screen during
the FFT waveform display.
Example FFT of 100MHz Sine wave
Because the input frequency (100MHz) is higher than 1/2 the sampling rate (100MHz),
aliasing occurs and the main component is displayed as 97.65MHz.
Since this product is equipped with an
independent counter function, the
occurrence of aliasing can also be
identified from those measured results.
The following methods are available to prevent aliasing.
•
When Length of ACQUISITION menu is short, select Long and set F Position to
“4096” to increase the FFT sampling rate.
•
With the time axis (YT) waveform displayed, turn the TIME/DIV knob clockwise,
increase the sampling rate, and widen the frequency axis range of the FFT result.
•
Using the band-limiting (BW) function or an external anti-aliasing filter, remove
components from the observed signal that are higher than the Nyquest frequency.
Prevention of Aliasing
FFT Sampling Rate
Counter Measurement