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# What is negative frequency

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#### yalanand

##### Junior Member level 2
hi can any one please explain to me the concept of negative frequency ?.

There is no negative frequency in reality... I guess that you mean on negative frequencu that you get from Furier transformations... Well these frequencies are from nature of Furier, because it is symetrical around y axis...

yes i am referring to frequency got from fourier trasforms...

That is pure mathematics...

Negative frequency

Think about phasors. In trigonometric Fourier series (an and bn) you don't need negative frequencies because the result is given by a sum of sines and cosines.

In exponential Fourier series(cn) the need for negative frequencies yields from the fact that for describing a real function with complex exponentials, it necessary two phasors, one turning clockwise and the other anti clockwise, thus the result is the proyection the phasors on the axis.

Tip: the phasors have same angular rate, same magnitude and opposite phase, that's the trick

It take me some time to write and remember, but here it is...

as u r talkin abt the negetive freq in Fourier transform...as it is said it is a mathematical outcome....why it comes is , when u look at the fourier transform of the signal...it will be represented in the exponentials. just imagine...wat if u change the sign of the exponentials, ie., amkin the freq negative? all u r goin to get is the repleca of the positive value of the same freq....just do this u will understand it better...
hope it helps u....

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