5.Advanced User Guidebook
FFT function in this oscilloscope transforms 2048 data points of the time-domain signal
into its frequency components mathematically 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.
To select the FFT window
■
There are four FFT windows. Each one has trade-offs 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 Characteristics
Window
Rectangle
Best solution for frequency, worst for magnitude.
Best type for measuring the frequency spectrum of
nonrepetitive signals and measuring frequency
components near DC.
Recommend to use for:
z
Transients or bursts, the signal level before and
after the event are nearly equal.
z
Equal-amplitude sine waves with frequencies
those are very close.
z
Broadband random noise with a relatively slow
varying spectrum.
Hamming
Better solution for magnitude than Rectangle, and
good for frequency as well. It has slightly better
frequency resolution than Hanning.
Recommend to use for:
z
Sine, periodic and narrow band random noise.
z
Transients or bursts where the signal levels
before and after the event are significantly
different.
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