User Manual

APPENDIX 19
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Appendix 3 Reference
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f(t)
Input signal
Time domain Frequency domain
t
ω
F(
ω
)
0 Fmax
Sampling
function
Fs > 2
Fmax
t
Fs > 2 Fmax
t
Fs > 2 Fmax
Sampling
function
Fs < 2
Fmax
t
Fs < 2 Fmax
t
Fs < 2 Fmax
Overlapped parts seem folded back
Fs/2
Section
observed on
screen
 Anti-aliasing filter
In FFT processing, when the frequency bandwidth of the input signal is
unlimited, frequency spectrum components that do not exist will appear, due
to aliasing. To prevent this, a low-pass filter is required which cuts off the
input waveform at 1/2 of the sampling frequency. Such a low-pass filter is
called an anti-aliasing filter.
The input module incorporates an anti- aliasing filter and therefore allows
the 8855 to perform FFT analysis without being subject to aliasing.