This visualiser was generated by Claude (Anthropic) as part of the Wireless 101 course materials. Every sample of the modulated signal, its envelope, the envelope-detector output, the sideband frequencies and the power efficiency are computed live from the formulas printed at the foot of the page — the signal is evaluated point by point, never sketched. Three kinds of number appear, each labelled where it is used: computed (everything the plots, the spectrum and the readouts show), published figure (none — the only constant here is 2π), and illustrative (the on-screen frequencies are a few hertz so the fast carrier and the slow envelope are both visible; the animation rate is for the eye). It does not measure anything and it does not call out to a server.
Standard AM (double-sideband, full carrier): s(t) = A₊[1 + m cos(2πfₘt)] cos(2πfₗt), with sidebands at fₗ ± fₘ and transmission efficiency η = m²/(2 + m²). Course source: M3-L2 amplitude modulation. The modulation index is written m throughout this course.
Build a standard AM signal, watch its envelope carry the message, recover the message with an envelope detector, and read the spectrum and the power efficiency. Raise the modulation index m for a deeper envelope — but push it past 1 and the envelope goes negative, the detector clips, and the message comes back distorted. Every curve and number is read off the computed samples, never drawn by hand.
A message tone multiplies a carrier to make the AM signal; its spectrum is a carrier line with a sideband each side; an envelope detector rectifies and smooths the signal to recover the message. Every thumbnail is computed from the same samples as the full-size panels — nothing here is an icon. Hover a block to highlight the panel and the knobs that feed it.
The thin blue curve is s(t) = A₊[1 + m cos(2πfₘt)]cos(2πfₗt), evaluated sample by sample. The dashed red curves are the envelope ±A₊[1 + m cos(2πfₘt)]; the thin green curve is the message the envelope traces. When m > 1 the upper and lower envelopes cross the axis and each other — that crossing is overmodulation.
An envelope detector outputs |envelope| and then removes the DC level. For m ≤ 1 the envelope never goes negative, so the recovered message (green) matches the original tone. For m > 1 the rectifier folds the negative dips back up, and the recovered message is clipped and distorted — compare the two curves.
The AM signal has three lines: the carrier at fₗ with amplitude A₊, and two sidebands at fₗ ± fₘ, each with amplitude m A₊/2. The carrier carries no information yet holds most of the power — that is what the efficiency readout measures.