User Manual 1. Press the [Math] button on the front panel to open the MATH function menu. 2. Press the Operation softkey and then turn the Multifunctional Knob to select FFT . The resulting math waveform is displayed on the screen and labeled with “M”. 3. Press the Source softkey, and then turn the Multifunctional Knob to select the source to do FFT operation. Analog channels (CH1~CH2) can be used as the source. 4. Press Center softkey and then turn the Multifunctional Knob to adjust the frequency of the frequency domain waveform corresponding to the horizontal center of the screen. 5.
Press Span softkey and then turn the Multifunctional Knob to adjust the the horizontal scale of the frequency domain waveform. 6. Press the Vertical Units softkey to select the unit of vertical axis. The units of the vertical axis can be dB or Vrms which use a logarithmic scale or a linear scale to display vertical amplitude respectively. 7. Press the Scale softkey to select the vertical scale. 8. Press the Window softkey, and then turn the Multifunctional Knob to select an appropriate window. Spectral leakage can be considerably decreased when a window function is used.
The series of scope provides six kinds of FFT window functions which have different characteristics and are applicable to measure different waveform. You need to select the window function according to different waveform and their characteristics. Please read the table below carefully to make an appropriate option according to the input signal. Rectangular Pulse or Transient Waveform Special-purpose window applicable to discontinuous waveform. This is actually the same as no windows. Hamming Transient or short pulse A litter bit better frequency resolution than Hanning.
Hanning Periodic Waveform Better frequency, poorer amplitude accuracy than Flattop Single frequency signal, search Blackman for higher order harmonics. The best amplitude resolution; the poorest frequency resolution Bartlett Narrow band signal with Better frequency resolution. stronger Flattop Periodic Waveform Better amplitude, poorer frequency accuracy than Hanning 9. Press the Show-Only softkey to select to display FFT operation results only and not display the source channel. Note: 1. Signals with DC components or deviation would cause an error or deviation of the FFT waveform components. To reduce the DC components, set the Channel Coupling to AC. 2.
To reduce the random noise and aliasing frequency components of repetitive or single pulse, set the Acquisition of the oscilloscope to Average. Using Cursors to measure FFT waveform To make cursor measurements, press the Cursors button to turn the cursors, and then press the Mode softkey to select Manual or Track, Use the AX and BX cursors to measure frequency values and the difference between two frequency values (BX-AX). Use the AY and BY cursors to measure amplitude in dB and difference in amplitude (BY-AY). 19 / 67 Window Measurement Characteristics