I know that all periodic continuous time signal have discrete spectral representations, but are all discrete spectral representations periodic in continuous time?
Also, can all periodic signals be represented by a fourier series?
I know that all periodic continuous time signal have discrete spectral representations, but are all discrete spectral representations periodic in continuous time?
Also, can all periodic signals be represented by a fourier series?
Nope! Consider:
$$\cos(t)+\cos(\pi t) $$
It's Fourier transform is certainly discrete, but the signal isn't periodic because $\pi$ is irrational. No integer multiple of periods is going to get you back to where you started.