Michael Cerna and Audrey F. Harvey
National Instruments

The Fast Fourier Transform (FFT) and the power spectrum are powerful tools for analyzing and measuring signals from plug-in data acquisition (DAQ) devices. For example, you can effectively acquire time-domain signals, measure the frequency content, and convert the results to real-world units and displays as shown on traditional benchtop spectrum and network analyzers. By using plug-in DAQ devices, you can build a lower cost measurement system and avoid the communication overhead of working with a stand-alone instrument. Plus, you have the flexibility of configuring your measurement processing to meet your needs.

To perform FFT-based measurement, however, you must understand the fundamental issues and computations involved. This application note describes some of the basic signal analysis computations, discusses antialiasing and acquisition front ends for FFT-based signal analysis, explains how to use windows correctly, explains some computations performed on the spectrum, and shows you how to use FFT-based functions for network measurement.