EE 350
LINEAR SYSTEMS ANALYSIS
FALL 2007
Laboratory #3: Fourier Spectra and Modulation
The objectives of the second laboratory are to:
•
Become familiar with HP 100 MHz oscilloscope as a signal analyzer.
•
Measure the magnitude of the Fourier amplitude spectra,

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, of a sinusoid, a square and a triangular wave.
•
Investigate the behavior of the spectral components of the product of two sinusoidal signals as the frequency
of the signals are varied.
•
Demonstrate envelope detection of an AmplitudeModulated(AM) signal.
1 HP 100 MHz Oscilloscope as a Signal Analyzer
The HP 54600series 100 MHz oscilloscope in the lab is equipped with HP 54657 Measurement/Storage module
that provides the scope with the capability to display the frequency spectra of the signal acquired on input 1, input
2, or the result in Function 1 (which to adds, subtracts, or multiplies the signals acquired on vertical inputs 1 and
2) and to display the result in Function 2.
The front panel of the oscilloscope has knobs, grey keys, and white keys. The grey keys bring up softkey menus
on the display that allow you access to many of the oscilloscope features. The white keys are instant action keys and
menus are not associated with them. In this writeup, the frontpanel keys are enclosed in square brackets and the
softkeys are denoted by boldface.
Generic steps to display the frequency spectra of a signal connected to the oscilloscope
1. Press [+/].
2. Toggle the
Function 2 On O±
softkey to enable math function number 2.
3. Press the
Function 2 Menu
softkey.
4. Toggle the
Operand
softkey until the desired source is selected.
5. Press the
Operation
softkey until FFT is selected. Results (F2) are displayed on the screen.
6. Press
FFT Menu
softkey. (FFT stands for Fast Fourier Transform which will be discussed at the end of the
semester.)
7. Press
Autoscale FFT
softkey. Rotate Time/Div knob to set the frequency span of the measurement.
8. Press the
FFT Menu
softkey. A softkey menu with six softkey choices appears. Five of them are related to
FFT:
•
Cent Freq
Allows centering of the FFT spectrum to the desired frequency. Select and rotate the knob closest to the
[Cursors] key to set the center frequency to the desired value.
•
Freq Span
Sets the overall width of the FFT spectrum (left graticule to the right graticule). Select and rotate the
knob closest to the [Cursors] key to set the center frequency to the desired value.
•
Move 0 Hz to Left
Pressing this key changes the center frequency so that the left most graticule represents 0 Hz.
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Autoscale FFT
The Autoscale FFT softkey will automatically set Units/Div and Ref Level to bring the FFT data on
screen.
•
Window
The signal on channel 1 is multiplied by a function called window. This softkey allows one of four windows
to be selected. Select and rotate the knob closest to the [Cursors] key to set the desired window.
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 Fall '07
 SCHIANO,JEFFREYLDAS,ARNAB
 Frequency, Hertz, Carrier wave

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