DeVry University
ECET345 Signals and Systems
Name of Student ___________________________
Class Room Activity #2
Experimental observation of aliasing
Objective of the lab experiment:
The objective of this experiment is to observe the effect of aliasing in a discrete sampling system and to measure how aliasing alters the frequency of an input signal that is beyond the Nyquist limit. This lab can also be used to quantitatively and qualitatively observe the effect of an antialiasing filter, even though we do not do so in this exercise.
Equipment list:
Tower system with ADCDAC board
Function generator capable of producing any desired frequency sinusoid up to 5 KHz
Oscilloscope
Three BNC to alligator
One PC running CodeWarrior 5.9
MATLAB
2.0 mm flat head screwdriver
Software Needed:
Axiom_Straight_Through_982Hz_Sampling.zip: Available in Doc Sharing.
Theory
Nyquist’s theorem states that for a digital sampling system with sampling frequency fs, it can accurately recreate a signal only if its frequency is or below. This is known as the Nyquist limit. When a digital sampling system is fed a signal that is above this limit, it cannot reconstruct the original signal, and the data are lost. At this point, an effect called aliasing occurs. As the input frequency increases past the Nyquist limit, the output will decrease until it is DC again at the sampling frequency. Beyond the sampling frequency, the output frequency will increase again. In this lab you will observe and record what happens to a signal that goes beyond the Nyquist limit and even beyond the sampling frequency.
Procedure:
Step 1
Refer to Appendix A for instructions on setting up the ADCDAC board.
Set up the analog-to-digital and digital-to-analog converter connections.
Connection
Use
Input on Channel 0 (ADC LTC 1857)
input from signal generator
Output on Channel A (DAC LTC 2620)
Filter A output (bipolar). Here just unfiltered Straight-through output
Channel B
Not used...