Tektronix DPO2304SX, Printable Help

Page: 290 / 920

FFT window characteristics
Each FFT window is a trade-off between frequency resolution and magnitude accuracy. What you want to measure and your
source signal characteristics help determine which window to use. Use the following guidelines to select the best window.
FFT window Characteristics Best for measuring
Rectangular Best frequency, worst magnitude
resolution. This is essentially the same as
no window. Transients or bursts where the signal
levels before and after the event are
nearly equal.
Equal-amplitude sine waves with
frequencies that are very close.
Hamming, Hanning Better frequency, poorer magnitude
accuracy than Rectangular. Hamming has
slightly better frequency resolution than
Hanning. Sine, periodic, and narrow-band random
noise.
Transients or bursts where the signal
levels before and after the event are
significantly different.
Blackman-Harris Best magnitude, worst frequency
resolution. Predominantly single frequency signals to
look for higher order harmonics.
You can also determine the best window empirically by first selecting the Rectangular window, and then selecting (in the
following order) the Hamming, Hanning, and Blackman-Harris windows until the frequency components merge. Use the window
just prior to where the frequencies emerge for the best compromise between resolution and amplitude accuracy.
■ Continue
■ Previous
Time domain gating
You can use time domain gating to select a specific segment of your signal for spectral analysis. Two controls, gate position and
gate duration, determine the location and size of the gate.
The resulting spectrum corresponds to the frequency components of the signal in the gated segment.
Time domain gating is inversely proportional to the resolution bandwidth of the spectral waveform. The narrower the gate, the
larger the resolution bandwidth and the lower the frequency resolution. To obtain the best frequency resolution, use as wide a
gate as possible.
■
Continue
■
Previous
Math setups
258 DPO70000SX, MSO/DPO70000DX, MSO/DPO70000C, DPO7000C, and MSO/DPO5000B Series