Appendix F: Miscellaneous
ft=COS2 π ft
ft=SIN2 π ft
90_
Figure F6: Phase and Delay
FFT Window Functions FFT calculates with limited data blocks. Also, since FFT calculations assume that the sampled data blocks are repeated infinitely, frequency error arises from
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 characteristic 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.
F18 | AWG2021 User Manual |