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Exp#7: Spectral Analysis
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Exp#7: Spectral Analysis of Digital Signals
Objectives
There are three objectives of this lab:
1.
To learn and practice interpretation of power spectra.
2.
To learn how to use the spectrum analysis software package.
3.
To demonstrate the effect of sampling frequency, and the Nyquist sampling theorem, on
discrete signals.
Part 1. Sine waves and square waves
Generate a 200Hz sine wave with 2V rms amplitude and 0V offset. Using the Digital Spectrum
Analyzer (DSA) component of the data acquisition software (Vbench), measure the power
spectrum of this signal. Make sure no other Vbench component (such as the VScope) is running
at the same time.
There are two important parameters to choose: the sampling frequency,
f
s
, and number of
samples,
n
. Make
f
s
a simple number, like 500, for example, and set
n
equal to some power of 2
(
e.g.
256, 512, 1024). These parameters can be modified under the [Edit/Settings/Acquisition]
menu options. You are encouraged to experiment with these and observe the effect of changing
them. When you have settings that are satisfactory, then note the peak frequency in the power
spectrum from the screen marker, and write it down. Remember to include an uncertainty
estimate. Save the data on disk using the "Generate Report" option. Save "Display 2" only,
which is the power spectrum. It will be saved in ASCII format can be read into a spreadsheet
later on.
Now do the same thing for a square wave with the same amplitude and frequency. You may like
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 '07
 Pottebaum

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