Spectrum Tutorial

Experiments to be performed with the FFT spectrum demonstration package.

You can access the package by clicking on the Java Applets tag on the home page www.utdallas.edu/~ivor/, then clicking on FFT. Or using the URL www.utdallas.edu/~ivor/cs6386/dabbler.html

Perform these experiments:

  1. Spectrum of sums of sinewaves
    1. click on "scale" (to change the spectrum plot to a log scale).
    2. click on "+" (so that we add the signals).
    3. click on "sin"
    4. change the sin frequency to 20
    5. click on "sin"
    6. change the sin amplitude to 10
    7. change the sin frequency to 40
    8. click on "sin"
    9. Note the equation and explain the spectrum.
  2. Spectrum of square wave
    1. click on "clear"
    2. click on "+"
    3. click on "square"
    4. Note the equation and explain the spectrum.
  3. Spectrum of square wave of higher pulse rep. freq.
    1. click on "clear"
    2. click on "+"
    3. change the square frequency to 8.0
    4. click on "square"
    5. Note the equation and explain the spectrum.
  4. Spectrum of noise signal
    1. click on "clear"
    2. click on "+"
    3. click on "noise"
    4. Note the equation and explain the spectrum.
  5. Spectrum of impulse
    1. click on "clear"
    2. click on "+"
    3. click on "impulse"
    4. Note the equation and explain the spectrum.
  6. Spectrum of sin(32t)(1+0.5sin(5t))
    1. click on "clear"
    2. click on "+"
    3. change the sin amplitude to 0.5
    4. change the sin frequency to 5.0
    5. click on "sin"
    6. click on "const"
    7. change the sin frequency to 32.0
    8. change the sin amplitude to 1.0
    9. click on "*" (to multiply the current signal by the next function)
    10. click on "sin"
    11. Note the equation and explain the spectrum.
  7. Spectrum of sin when block length != multiple of period
    1. click on "clear"
    2. click on "+"
    3. change the sin frequency to 2.5
    4. click on "sin"
    5. Note the equation and explain the spectrum.
  8. Spectrum of sin when block length != multiple of period * raised cosine
    1. click on "clear"
    2. click on "+"
    3. change the sin frequency to 2.5
    4. click on "sin"
    5. click on "*"
    6. click on 1/2(1-cos) (raised cosine)
    7. Note the equation and explain the spectrum.
  9. Spectrum of sampled triangle*raised cosine
    1. click on "clear"
    2. click on "+"
    3. click on "triangle"
    4. click on "*"
    5. click on 1/2(1-cos) (raised cosine)
    6. change the impulse frequency to 16.0
    7. click on "impulse"
    8. Note the equation and explain the spectrum.
  10. Spectrum of sampled sin
    1. click on "clear"
    2. click on "+"
    3. click on "sin"
    4. click on "*"
    5. change the impulse frequency to 16.0
    6. click on impulse
    7. Note the equation and explain the spectrum.
  11. Spectrum of sampled sin at higher frequency
    1. click on "clear"
    2. click on "+"
    3. change the sin frequency to 5.0
    4. click on "sin"
    5. click on "*"
    6. change the impulse frequency to 16.0
    7. click on impulse
    8. Note the equation and explain the spectrum.