Fourier
Problem
Problem
Freq4P05
Name_______________________________________
Here is some data that was taken for a signal. Dr. Abner Mallity
expected this signal to be periodic, and he needs to determine the frequency.
Now, either there isn't a periodic signal here, or there is just so much
noise that you can't see it. Here's the signal.
For the record, you
need to know this about the signal.
-
The signal record length
is 500 milliseconds (i.e. one half second).
-
The sampling interval
is 1 millisecond, so there are 500 points.
Dr. Mallity has taken the FFT of the signal, and that's shown below.
(It's a magnitude plot.) (Oh, and he did this in Mathcad, so the
smallest index is 0 - not 1 like in Matlab.)
Dr. Mallity notices
that there is a serious spike in the FFT, so he suspects that there might
be a periodic signal after all. He decides to magnify the horizontal
scale, and gets the plot below.
Answer the following
questions for Dr. Mallity.
-
Is there a periodic signal
embedded in the noise? Why?
-
If there is a periodic
signal, what is the frequency?
-
Is there any evidence
that the possible periodic signal is a sine wave?