AM and FDM Modulation Demo

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AM and FDM Modulation Demo#

Build an AM signal from a message and a carrier, and watch it in both the time domain and the frequency domain. Single AM mode goes with Lesson 28. FDM mode stacks three channels onto one spectrum and goes with Lesson 29.

Interactive demo · AM / FDM Modulation · Lessons 28–29 Open full-screen ↗

Things to Try#

  • Sweep the modulation index. Hold the message amplitude \(A_m\) steady and change the DC bias \(B\) (labelled b in the demo). Watch the gauge move through under-modulated, 100%-modulated, and over-modulated, and watch what happens to the envelope each time.

  • Find the sidebands. Switch to the Frequency Domain tab and change the message frequency \(f_m\). The sidebands sit at \(f_c \pm f_m\).

  • Check the efficiency. Note the efficiency readout at \(\alpha = 1\), then lower \(\alpha\) and see how much of the transmitted power is left for the message.

  • Share the spectrum (Lesson 29). In FDM mode, move two carrier frequencies toward each other until their channels overlap in the combined spectrum.

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