How to get Magnitude Spectrum of a Cosine Wave

Question

Upesh 2014-8-29

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/152720-how-to-get-magnitude-spectrum-of-a-cosine-wave

回答： Salaheddin Hosseinzadeh 2014-9-11

im trying to get magnitude spectrum of a cosine wave x(t)=cos(2*pi*fo*t),0<t<T; where fo=2000hz and sampling frequency Fs=32kHz.Also,samples need be generated at the rate of Fs over a time interval T. (signal length T has to be chosen such that there are 1024 samples of the simulated analog signal).

im not getting the correct spike...

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Salaheddin Hosseinzadeh 2014-8-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/152720-how-to-get-magnitude-spectrum-of-a-cosine-wave#answer_150159

Hi Upsesh,

This can be solved by properly using fft (Fast Fourier Transform)

I wrote a fftplot function wich plots the magnitude and returns the coeffs, I'll attach it here, have a look at it and you'll learn how to use FFT. I'll also attach a PDF file regarding how to use FFT.

Hope this helps.

Good Luck!

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Upesh 2014-8-29

thanks for the help..really appreciated.

请先登录，再进行评论。

Answer 2

Salaheddin Hosseinzadeh 2014-9-11

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/152720-how-to-get-magnitude-spectrum-of-a-cosine-wave#answer_151408

在 MATLAB Online 中打开

Hi Lizy,

Please do us a favor

1- edit your code so that we can read it. As it's really hard to follow, make it something like this

    sample = 1000;
    fs = 500;

2- Why don't you use, the files I attached in my previous answer? (the one above). If you don't like my code at least you can use MATLAB's imbedded fft function which take the Fourier transform of your signal?!

Please try the files provided, in the accepted answer or try fft and if you still had problem let us know.

doc fft

Good Luck

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

Answer 3

Lizy 2014-9-9

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/152720-how-to-get-magnitude-spectrum-of-a-cosine-wave#answer_151120

Hi, I need help to plot magnitude spectrum.. I've tried the following codes but it seems not working.. pls help ... thanks in advance ..

sample= 10000; % contains 10000 points -- sampling frequency f = 500; t = linspace(-f,f,sample+1); % frequency vector -500Hz<= f<500Hz t = t(1:end-1)

figure S2f = exp((-j*4*pi*f)./(2+j*2*pi*f)^2)+((1./200*pi)*(sin(inf)-sin(400*pi))); S2f_mag = abs(S2f); plot(S2f_mag) % plot magnitude spectrum title('Magnitude Spectrum S2(f)') hold on