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Appendix F: Miscellaneous
FĆ18
AWG2021 User Manual
f(t)=COS(2 π ft)
f(t)=SIN(2 π ft)
90_
Figure FĆ6: Phase and Delay
FFT calculates with limited data blocks. Also, since FFT calculations assume
that the sampled data blocks are repeated infinitely, frequency error arises from
non-continuities generated at the edges of data blocks. This frequency error is
called leakage error.
The leakage error depends on the FFT window function selected. The processing
to bring the window function at both ends towards 0 in order to give the FFT
continuity is called taper processing. This instrument has the square wave
window, which does not apply taper processing to the time region data, and five
FFT window functions that do carry out taper processing.
The FFT window functions in the time region correspond to filters in the
frequency region. This is convolution and it is well known that it has a character-
istic of sin(x)/x for square window. These filters have a high lobe at the center, in
other words a transmitting band width,. This lobe determines how great the
neighboring frequency components can be separated.
The transmission amount for the side lobes neighboring this center lobe
determines the amount of leakage. Leakage is the spread of energy from a certain
frequency component for the displayed frequency spectrum. Frequency
components with small magnitudes are covered overall by leakage.
FFT Window Functions