Basic Operation 2. Set the Operation option to FFT; 3. Select the Math FFT Source channel. In many situations, the oscilloscope can also generate a useful FFT spectrum despite the YT waveform not being triggered. This is especially true if the signal is periodic or random (such as noise). Note: You should trigger and position transient or burst waveforms as close as possible to the screen center. Nyquist Frequency The highest frequency that any real-time digital oscilloscope can measure without errors is half of the sample rate, which is called the Nyquist frequency. Frequency information beyond the Nyquist frequency is undersampled which brings about the FFT aliasing.
The math function can convert the center 2048 points of the time-domain waveform to an FFT spectrum. The resulting FFT spectrum contains 1024 points from DC (0Hz) to the Nyquist frequency. Usually, the screen compresses the FFT spectrum horizontally to 250 points, but you can use the FFT Zoom function to expand the FFT spectrum so that you can clearly view the frequency components at each of the 1024 data points in the FFT spectrum. Note: The oscilloscope’s vertical response is a little bit larger than its bandwidth (60MHz, 100MHz or 200MHz, depending on the model; or 20MHz when the Bandwidth Limit option is set to Limited).
Therefore, the FFT spectrum can display valid frequency information above the oscilloscope bandwidth. However, the amplitude information near or above the bandwidth will not be accurate. 5.3.1.2 Displaying FFT Spectrum Push the MATH MENU button to display the Math menu. Use the options to select the Source channel, the Window algorithm and the FFT Zoom factor. Only one FFT spectrum can be displayed at a time. DSO1000B(V) Series HandHeld Oscilloscope User Manual 21 Math FFT Settings Comments Options Source CH1, CH2 Choose a channel to be the FFT source. Window Hanning, Flattop, Rectangular, Bartlett, Blackman Select a type of the FFT window. For more information, refer to Section 5.3.1.3.
FFT Zoom X1, X2, X5, X10 Change the horizontal magnification of the FFT display. For detailed information, refer to Section 5.3.1.6. Vertical Base dBrms, Vrms Set dBrms to be the vertical base; Set Vrms to be the vertical base