I am trying to make a cos function at 19.8kHz, but the function produced by cos does not look like one, why is that?

%% Time specifications:

   Fs = 80000;                   % samples per second

   dt = 1/Fs;                   % seconds per sample

   StopTime = 0.25;             % seconds

   t = (0:dt:StopTime-dt)';     % seconds

   %%Sine wave:

   Fc = 19800;                     % hertz

   x = cos(2*pi*Fc*t);

This is what I did, and what I got from the plot command. What is the correct way to get a cos graph?

[Stephen23]

"What is the correct way to get a cos graph?"

By generating enough samples. Your sample rate is way too low.

Answer 1

[David Goodmanson]

Hi Justin,

right now you are seriously undersampled on the cosine wave. You have 80000/19800 = 4.04 samples per cycle, so you catch very few points on the wave. If you raise your sampling frequency by a factor of 5 or 10 you will see much better results.