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FFT spectrum analysis
•
Using FFT algorithm you can convert the domain signals (YT) into frequency
domain signals.
•
With FFT you can observe the following types of signals:
1.
Measure the harmonic wave composition and distortion of the system.
2.
Demonstrate the noise characteristics of the DC power.
3.
Analyse oscillation.
•
Signals with DC quantities or DC offset will cause error or offset FFT waveform
quantities. To reduce DC quantities select AC coupling.
•
To reduce random noise and frequency aliasing as a result of repeated or single
pulse event, set the acquired mode of the oscilloscope to average acquisition.
•
Press MATH button then F1 to select FFT and enter the FFT menu.
Functions Menu
Type
Signal source
Window
Vertical Unit
Select the FFT window
•
Assuming the YT waveform is constantly repeating itself, the oscilloscope will carry
out FFT conversion of time record of a limited length. When this cycle is a whole
number, the YT waveform will have the same amplitude at the start and finish.
There is no waveform interruption.
•
If the YT waveform cycle is not a whole number there will be different amplitudes
at the start and finish, resulting in transient interruption of high frequency at the
connection point. In frequency domain this is known as leakage.
•
To avoid leakage multiply the original waveform by one window function to set the
value at 0 for start and finish compulsively. See the following table:
Setup
FFT
CH1 to CH4
Hanning
Hamming
Blackman
Rectangle
Vrms, dBVrms
26
Notes
To carry out FFT algorithm functions
Set CH1 to CH4 as FFT source
Set Hanning window function
Set Hamming window function
Set Blackman window function
Set Rectangle window function
Set vertical unit as linear or dB (log)
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