9-17
9
IM 701830-01E
Waveform Analysis
9.8
Displaying Power Spectrums
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For a description of this function, refer to page 1-21.
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Function
This function displays the power spectrum of the waveform on CH1/2/5.
Math1(Basic) : PS(C1), PS(C2)
Math2(Basic) : PS(C5)
If CH1/2/5 is set to logic input, however, the power spectrum is not displayed.
Points
Select 1000, 2000, or 10000.
The instrument applies FFT to the selected number of points (beginning at the specified Start
Point) to generate the power spectrum.
Window
Selects the time window. Select either of the following.
Rect
: Rectangular window; useful for transient signals that attenuate completely within the
window.
Hanning : Useful for continuous but nonperiodic signals.
Flattop : The frequency resolution drops as compared to the Hanning window, but is effective
in increasing the level accuracy.
Restrictions
• This function does not operate while the instrument is in envelope mode.
• If the display record length is less than the selected number of points for the computation,
this operation cannot be executed.
• If the bandwidth limit is set to Auto on the High-Resolution, High-Voltage, Isolation/High-
Resolution, Isolation Modules, the anti-aliasing filter becomes active.
• The horizontal axis of the FFT displays half of the frequencies of the sampling rate (or data
update rate) of each module as defined by the Nyquist Theorem. For example, if the
measurements are made at 10 MS/s and 100 kS/s, the frequencies become 5 MHz and 50
kHz, respectively. However, if modules with different maximum sampling rates (or data
update rates) coexist and if the measurement is made at frequencies higher than the maximum
sampling rate of some modules, the data for those modules will not be displayed correctly.
In this case aliasing occurs in which the low frequency data are displayed in the high
frequency region. Please be aware that the display that results from aliasing does not reflect
the actual signal.
Operating Procedure
1.
Press the
MATH
key.
2.
Press the “
Mode
” soft key as necessary to select “
Basic
.”
3.
Press the “
Math1
” soft key and select “
PS(C1)
” or “
PS(C2)
,” or press the “
Math2
” soft
key and select “
PS(C5)
.”
4.
Press the “
Next
” soft key to display the “
Next 2/2
” menu.
5.
Press the “
FFT
” soft key to open the Select menu.
6.
Turn the jog shuttle to move the cursor to the “
Points
” item, and then press the
SELECT
key as necessary to select the number of points.
7.
Turn the jog shuttle again to move the cursor to the “
Window
” item. Press the
SELECT
key to choose the window.
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