A laboratory project in which the students build a simple DC to 1 MHz
spectrum analyzer using only an oscilloscope, function generator, and
a custom-built mixer/IF section is described. After assembling the spe
ctrum analyzer, the students use it to explore the spectra of a number
of different waveforms including amplitude- and frequency-modulated s
ine waves. The laboratory helps the students develop a feel for the me
aning and significance of the mathematics they have learned relating t
he time- and frequency-domain representations of signals (i.e., the Fo
urier series, and Fourier and Laplace transforms). In addition, the la
boratory introduces the students to mixing (i.e., heterodyning) and im
proves their understanding of their test equipment and its possible us
es. The laboratory is suitable for use in a typical junior-level signa
ls and systems course, a junior-level circuits course, a communication
course, or a measurement course.