This Demonstration shows a tone-modulated sine wave in the time domain and in the frequency domain. Available analog modulation types are amplitude modulation (AM), double-sideband suppressed-carrier modulation (DSB-SC), and frequency and phase modulation (FM and PM). The frequency of the modulating tone is . The AM spectrum is composed of a spectral line at the carrier frequency and two lines at above and below the carrier. The DSB-SC spectrum has no carrier. FM and PM have identical spectra, composed of spectral lines apart. The modulation index μ or β describes how much the carrier signal varies around its unmodulated level. The bandwidth of FM and PM is much higher compared to AM.
AM: , modulation index:
FM: , modulation index:
PM: , modulation index:
The spectrum is calculated from 4096 samples of by means of the discrete Fourier transform (DFT).