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© National Instruments Corporation 11 NI Spectral Measurements Toolkit User Guide
Figure 2. Zoom FFT Technique
FFT algorithms usually perform baseband analysis by displaying the
spectrum from zero to the Nyquist frequency. However, a standard FFT
might not be effective if you need to obtain a higher frequency resolution
over a limited portion of the spectrum or if you need to zoom in on details
of a spectral region. The zoom FFT uses algorithms to avoid the amount of
calculation required using a long standard FFT to obtain high-frequency
resolution over an entire spectrum.
You can define the frequency resolution of an analysis, df, using the
following formula:
df = f
s
/N = 1/T
where f
s
is the frequency of the sampled signal
T is the time duration
N is the number of samples
Only the acquisition time determines the analysis resolution. You can either
decrease f
s
or increase N to improve df.
The Spectral Measurements Toolkit supports two algorithms for zoom FFT
processing: continuous zoom FFT and block zoom FFT.