Analog Modulation

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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.

Contributed by: Carsten Roppel (August 2018)
Open content licensed under CC BY-NC-SA


Modulating signal:

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).


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