National Instruments Toolkit Using Spectral Measurements Toolkit Techniques

NI Spectral Measurements Toolkit User Guide 10 ni.com

The Cross Power Spectrum Measurement example is located at samples\

smt\simulated\smtcrspwr\smtcrspwr.prj.

This example demonstrates how to configure the zoom FFT, then calculates

the averaged power spectrum of a stimulus and response signal from

a device under test and the averaged cross spectrum between these

twosignals. The example uses the continuous zoom FFT technique and

demonstrates how you must create a unique handle for the stimulus data

(handle1) and response data (handle2). Use handle1 when you calculate

the continuous zoom FFT and averaged power spectrum on the stimulus.

Use handle2 when you calculate the continuous zoom FFT and averaged

power spectrum on the response. You can use either handle1 or handle2

when you calculate the averaged cross power spectrum between the

stimulus and the response.

Using Spectral Measurements Toolkit Techniques

The Spectral Measurements Toolkit contains tools for block and

continuous zoom processing and spectrum averaging. You can specify the

zoom characteristics in terms of center frequency, span, and resolution

bandwidth. You can use spectrum averaging to reduce the effect of noise

on your measurement system.

The Spectral Measurements Toolkit uses the zoom FFT technique to

analyze the frequency spectra of stationary signals. This technique allows

you to zoom in on a small portion of the frequency spectrum with

high-frequency resolution by using fewer calculations than a standard FFT.

Figure 2 illustrates how a zoom FFT detects the presence of two tones of

closely spaced frequencies. The standard FFT, shown in the upper graph,

indicates a single peak, and the zoomFFT, shown in the lower graph,

indicates the presence of two separate tones in the signal.