User Manual

Please press OPTION ◄ and OPTION ► menu button to adjust the position of the waveform along the
horizontal position. "FFT -2.00DIV (500.0Hz) " shown on the left bottom means the section start of the
waveform departures from the Origin for 2.00DIV, that is 250Hz/DIV.The shown frequency of M is the
exact frequency of the cursor point in the middle of spectrum. Shown as Figure.54. Press OPTION ◄
and OPTION ► to adjust horizontal base on horizontal base such as "250Hz/DIV （5kS/s）".
Figure 54
7.13.1. Selecting an FFT Window
The FFT feature provides four windows. Each is a trade-off between frequency resolution and magnitude
accuracy. What you want to measure and your source signal characteristics help determine which window to
use. Use the following guidelines to select the best window.
Type
Description
Window
Rectangular
This is the best type of window for resolving frequencies
that are very close to the same value but worst for
accurately measuring the amplitude of those
frequencies. It is the best type for measuring the
frequency spectrum of non repetitive signals and
measuring frequency components near DC.
Use Rectangular for measuring transients or bursts
where the signal level before and after the event are
nearly equal. Also, use this window for equal-amplitude
sine waves with frequencies that are very close and for
broadband random noise with a relatively slow varying
spectrum.
Hamming
This is a very good window for resolving frequencies that
are very close to the same value with somewhat
improved amplitude accuracy over the rectangular
window. It has a slightly better frequency resolution than
the Hanning.
Use Hamming for measuring sine, periodic and narrow
band random noise. This window works on transients or
bursts where the signal levels before and after the event
are significantly different.
Hanning
This is a very good window for measuring amplitude
accuracy but less so for resolving frequencies.
Use Hanning for measuring sine, periodic and narrow
band random noise. This window works on transients or
bursts where the signal levels before and after the event
are significantly different.
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