Fast Fourier Transforms
3–40
TDS 420A, TDS 430A, TDS 460A & TDS 510A User Manual
FFT Time Domain Record
FFT Time Domain Record
After Windowing
FFT Window
FFT Frequency Domain Record
FFT
Xs
Figure 3–22: Windowing the FFT Time Domain Record
Window Characteristics. When evaluating a window for use, you may want to
examine how it modifies the FFT time domain data. Figure 3–23 shows each
window, its bandpass characteristic, bandwidth, and highest side lobe. Consider
the following characteristics:
The narrower the central lobe for a given window, the better it can resolve a
frequency.
The lower the lobes on the side of each central lobe are, the better the
amplitude accuracy. The Hanning and Blackman/Harris windows taper the
data at the end of the record to zero.
Narrow lobes increase frequency resolution because they are more selective.
Lower side lobe amplitudes increases accuracy because they reduce leakage.
When using bell shaped widows, be sure that the most interesting parts of the
signal in the time domain record are positioned in the center region of the
window so that the tapering does not cause severe errors.
To Next Page
Loading...
