HOW CAN I BROADEN MY SIN SIGNAL

I need to plot a sin signal and analyse it using a spectrum analzer (periodogram) but i want to broaden the sin signal how is it possible??

[Image Analyst]

Do you mean (1) you want to increase the period (wavelength) of a perfect sine wave? Or (2) are you looking at it's spectrum, which would be a delta function, and wanting to broaden it from a delta function into something wider, like a sinc function (which you'd get by multiplying your sine by a rectangular window in the spatial domain), indicating that there are more frequencies present now than just your original frequency of your original sine wave? Which case is it, #1 or #2?

[raj]

case 2

[raj]

i want my sin signal now to spread among the other frequency bins also

Answer 1

[raj]

sin broadening can be taken as a chirp signal or even considering two sin signals which are very close in there frequencies that they cannot be resolved then we can see there is sin broadening

[Walter Roberson]

chirp signals do not have flat-topped peaks.

Anyhow, you marked the question as Accepted, so you have come up with an answer suitable for your purpose, right?

Answer 2

[Rick Rosson]

Multiply your sine wave by a narrow window function.

[raj]

I have that in mind but I am not allowed to do that

[Walter Roberson]

You could give us a hint as to what you _are_ allowed to use.

[raj]

I want to generate a spectrum where the sin signal of certain frequency component should not look peaky but must spread among other frequency bins

[Walter Roberson]

If that is your only requirement, then why are you not _allowed_ to multiply your sine wave by a narrow window function? What other restriction have been placed on the form of your solution?

[raj]

The peak should be flat so it is naturally spread among many frequency bins

Answer 3

[Image Analyst]

How about using conv() to convolve your perfect sine signal with some crazy kernel?

[raj]

I didnt get you but can you give the code so that I can try it.

Answer 4

[Honglei Chen]

Are you just looking for a sin that does not fall on an exact frequency sampling point so on the graph it seems having some kind of leakage, like the code below does?

fs = 128;
N = 32;
f = 10;
t = (0:N-1)/fs;
x = sin(2*pi*f*t);
Nfft = 128;
plot((0:Nfft-1)/Nfft*fs,abs(fft(x,Nfft)))

This doesn't really broaden your sin signal though.

Answer 5

[Rick Rosson]

Hi Raj,

We are not mind readers, and we are not really interested in pulling teeth to figure out what you need. Please tell us exactly what you are trying to do, why you want to do it a certain way, and what specific constraints or restrictions you are facing.

Also, if you have any MATLAB code that you have started developing, please post it and ask us specific questions related to your code.

Thanks!

Rick

[Walter Roberson]

For example are you looking for the equivalent of a zero-order hold but applied in the frequency domain ?

Answer 6

[raj]

sin broadening can be taken as a chirp signal or even considering two sin signals which are very close in there frequencies that they cannot be resolved then we can see there is sin broadening