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Could a good soul help me?

I heard that the fourier transform of a periodic signal is a pulse train, but for a sawtooth wave: what is the fundamental frequency of the spectrum?


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You heard wrong. A pulse train is it's own Fourier transform. Also, you'll have to reword what you mean by the fundamental frequency of the spectrum. Since the spectrum of a sampled signal repeats every $2\pi$ radians/sample, one might say that is the fundamental frequency of them all. – AnonSubmitter85 Jun 23 '13 at 9:11

The fundamental frequency is the inverse of the period (if you measure phase in cycles) or $2 \pi$ divided by the period (if you measure in radians). The Fourier expansion is shown here as $\dfrac 2\pi\displaystyle \sum_{k=1}^{\infty}(-1)^{k+1}\frac {\sin(2k\pi f t)}k$

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Thanks, but I think you are explaining the fourier series not the fourier transform. – juanma2268 Jun 3 '13 at 22:12
For a periodic function, they are the same. There is only energy at harmonics of the period. – Ross Millikan Jun 3 '13 at 22:47

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