## Spectrum of FSK

The spectrum of the FSK signal is not as easy to derive as that for ASK because the FSK generation process is non-linear. An approximation can be obtained by plotting the spectra for two ASK streams centred on the respective carrier frequencies. Clearly, the overall bandwidth occupied by the FSK signal depends on the separation between the frequencies representing the symbol states. An FSK system using continuous phase transitions will have much lower side-lobe energy than the discontinuous case. |

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