User Manual

Operating Manual for UTD2000/3000
Selection of FFT window
Mathematical storage oscillograph will carry out F FT conversion for time r ecord 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
y
multiplying original waveform by a window function to avoid leakage. Please refer to following form for
application of window function
.
Form 2-
4
24
FFT window
Characteristic
s
The most appropriate measurement content
Rectangle
The best frequency and the poorest
amplitude resolution to be basicall
y
similar to circumstances without window
;
Transient or short impulse with basically equivalent
signal level; Sine with equivalent amplitude wit
h
similar frequency; Wide band random noise of wave
spectrum with slow variation
;
Hannin
g
With excellent frequency resolution and
poor amplitude resolution by comparin
g
with rectangular window
;
Sine, cycle and narrow band random noise
Hammin
g
Frequency resolution of Hamming window
is better than that of Hanning window slightly
.
Transient or short impulse with large difference
for signal level
;
Blackma
n
The best amplitude resolution and the
poorest frequency resolutio
n
Mainly used for single-frequency signal to search
for higher order of harmonic wave
.