Basic Operation 5.3.1 Math FFT This chapter elaborates how to use the Math FFT (Fast Fourier Transform). You can use the Math FFT mode to convert a time-domain (YT) signal into its frequency components (spectrum), and to observe the following types of signals: ➢ Analyze harmonics in power cords; ➢ Measure harmonic content and distortion in systems; ➢ Characterize noise in DC power supplies; ➢ Test impulse response of filters and systems; ➢ Analyze vibration. To use the Math FFT mode, perform the following tasks:
➢ Set the source (time-domain) waveform; ➢ Display the FFT spectrum; ➢ Choose a type of FFT window; ➢ Adjust the sample rate to display the fundamental frequency and harmonics without aliasing; ➢ Use zoom controls to magnify the spectrum; ➢ Use cursors to measure the spectrum. 5.3.1.1 Setting Time-domain Waveform It is necessary to set the time-domain (YT) waveform before using the FFT mode. Follow the steps below. 1. Push the AUTO button to display a YT waveform. 2. Click the Vertical Position key to vertically move the YT waveform to the center (zero division) so as to ensure the FFT will display a true DC value. 3.
Click the Horizontal Position key to position the part of the YT waveform to be analyzed in the center eight divisions of the screen. The oscilloscope uses the 2048 center points of the time-domain waveform to calculate the FFT spectrum. 4. Click the VOLTS Key to ensure the entire waveform remains on the screen. If the entire waveform is invisible, the oscilloscope may display wrong FFT results by adding high-frequency components. 5. Click the TIME/DIV key to provide the resolution you need in the FFT spectrum. 6. If possible, set the oscilloscope to display multiple signal cycles.
If you Click the TIME/DIV key to select a faster setting (fewer cycles), the FFT spectrum will display a larger frequency range and reduce the possibility of FFT aliasing. To set the FFT display, follow the steps below. 1. Push the M/R button; DSO1000B(V) Series HandHeld Oscilloscope User Manual 20