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4.Advanced User Guidebook
85
4. In the bottom menu, select Format. In the right menu, select amplitude unit
(V RMS, Decibels) or phase unit (Radian, Degrees).
5. In the bottom menu, select Display. In the right menu, select Hori (Hz);
select repeatedly to make the symbol in front of the horizontal position
value (the upper one), click or to adjust the horizontal position of
FFT waveform; then select to make the symbol in front of the time base
value below, click or to adjust the time base of FFT waveform.
6. Select Vertical in the right menu; do the same operations as above to set
the vertical position and vertical division.
To select the FFT window
■ There are 6 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
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:
Sine, periodic and narrow band random noise.
Transients or bursts where the signal levels
before and after the event are significantly
different.
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:
Transients or bursts, the signal level before
and after the event are nearly equal.
Equal-amplitude sine waves with frequencies
those are very close.
Broadband random noise with a relatively
slow varying spectrum.
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