Using Fft Function - Owon SDS6062 User Manual

5. Advanced User Guidebook

Using FFT function

An FFT breaks down signals into component frequencies, which the oscilloscope uses
to display a graph of the frequency domain of a signal, as opposed to the oscilloscope's
standard time domain graph. You can match these frequencies with known system
frequencies, such as system clocks, oscillators, or power supplies.
FFT in this oscilloscope can transform 2048 points of the time-domain signal into its
frequency components and the final frequency contains 1024 points ranging from 0Hz to
Nyquist frequency.
Taking the FFT operation for example, the operation steps are as follows:
1. Press the Math button and call out the Math menu.
2. Press the H2 button and call out the FFT menu.
3. Press the F1 button to choose CH1 as the source.
4. Press F2 button, the windows item will display at the left of the screen, turn the M
knob to select Window, including Rectangle、Hamming、Hanning and Blackman.
5. Press F3 button to choose the Format, including dB, Vrms.
6. Press F4 button, the zoom window will display at the left of the screen, turn the M
knob to zoom in or out the wave of the multiple including ×1, ×2, ×5, ×10.
Selecting the FFT Window
■ The FFT feature provides four windows. Each one is a trade-off between frequency
resolution and magnitude accuracy. What you want to measure and your source signal
characteristics help you to determine which window to use. Use the following guidelines
to select the best window.
Type
This is the best type of window for resolving
frequencies that are very close to the same value
but worst for accurately measuring the amplitude of
those frequencies. It is the best type for measuring
the frequency spectrum of nonrepetitive signals and
measuring frequency components near DC.
Rectangle
Use rectangle for measuring transients or bursts
where the signal level before and after the event are
nearly
equal-amplitude sine waves with frequencies that
are very close and for broadband random noise with
a relatively slow varying spectrum.
This is a very good window for resolving
frequencies that are very close to the same value
Hamming with somewhat improved amplitude accuracy over
the rectangle window. It has a slightly better
frequency resolution than the Hanning.
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Description
equal. Also, use
User Manual of Smart Digital Storage Oscilloscope
this window for
Window