We know from books that if we do a fourier transform on a sinosoid, we get a delta function. I wonder why are we not getting a delta function when we pump a sine wave into a spectrum.

You may have misinterpreted the equation for the Fourier transform of a sinewave. You may have been referring to the Fourier transform of an impulsive signal, not a continuous sinewave.

The Fourier transform of a sine function is as follows:

Sin (2 pi w0 t) = (1/2) i [d(w + w0) – d(w – w0) ]

You may have misinterpreted the equation for the Fourier transform of a sinewave. You may have been referring to the Fourier transform of an impulsive signal, not a continuous sinewave.

The Fourier transform of a sine function is as follows:

Sin (2 pi w0 t) = (1/2) i [d(w + w0) – d(w – w0) ]

Regards -

Edited by: tabbott on Mar 10, 2014 2:17 PM