A
Fourier Series Problem
Problem
Freq4P00BInt
This is a guided problem to help you with basic Fourier Series concepts.
If you click here you can get
a calculator that allows you to enter Fourier coefficients and see the
resulting signal. Use that calculator for the questions below, as
needed.
In this problem, we assume that the Fourier Series is given by:
Problems
P1
The Fourier Series for a triangle wave - shown below - has components
that are given by:
-
ak =
8A/(p2k2)
as long as k is odd
-
ak =
0 for even k.
-
bk =
0 for all k because the function is even, so there are no sine terms in
the expansion.
-
What is the fundamental
cosine component when the amplitude is 10v?
P2
What is the value of the third harmonic?
P3
What is the value of the sine term in the third harmonic?
Now, compute the first five coefficients (for harmonics 1,3,5,7,9) for
a triangle wave with an amplitude of one, and with even symmetry (cosine
expansion), and insert your computed values into the simulator. Then
run the simulator and observe the quality of the triangle wave.
Next, do the same for a square wave. Use the same simulator, or you
can use the special square wave calculator. Click
here for the square wave simulator. Then answer this question.
P4
Is the quality better for the triangle wave with harmonics 1,3,5,7 &
9, or for the square wave with the same harmonics?
Now, consider what happens when the triangle signal is shifted in
time so that the positive-going zero crossing occurs at the time origin
as shown in the figure below.

P5
Answer the following questions.
-
What is the fundamental
cosine component when the amplitude is 10v?
-
What is the fundamental
sine component when the amplitude is 10v?
P6
You should be able to address these issues.
-
When the time origin shifts,
the size of the component at each harmonic stays the same.
-
However, when the signal
is odd, you will only have sine components.
-
When the signal is even,
you will have only cosine components.
-
The magnitude of the component
will be the same, but the sign can be different.
-
You can use the simulator
to check what hapens.