Operating Manual for UTD2000/3000
Selection of FFT window
Mathematical storage oscillograph will carry out FFT conversion for time record with limited length when
assuming continuous repetition of YT waveform. YT waveform will have the same amplitude in beginning
and ending locations for no interrupation. However, high-frequency transient interruption will be caused in
connector due to different waveform amplitudes for non-integral cycle of YT waveform. Such effect shall be
called as leakage in frequency domain. Therefore, value in forced beginning and ending locations is 0 b
multiplying original waveform by a window function to avoid leakage. Please refer to following form for
application of window function
24
FFT window
Characteristic
The most appropriate measurement content
Rectangle
The best frequency and the poorest
amplitude resolution to be basicall
similar to circumstances without window
Transient or short impulse with basically equivalent
signal level; Sine with equivalent amplitude wit
similar frequency; Wide band random noise of wave
spectrum with slow variation
With excellent frequency resolution and
poor amplitude resolution by comparin
Sine, cycle and narrow band random noise
Hammin
Frequency resolution of Hamming window
is better than that of Hanning window slightly
Transient or short impulse with large difference
for signal level
The best amplitude resolution and the
poorest frequency resolutio
Mainly used for single-frequency signal to search
for higher order of harmonic wave
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