Plot[2(1+0.3 Sin[500 t])*Sin[20000 t],{t,0,0.03},Frame->True,PlotLabel->"Première onde modulée"]

Plot[2(1+0.8 Sin[800 t])*Sin[30000 t],{t,0,0.02},Frame->True,PlotLabel->"Deuxième onde modulée"]

ParametricPlot[{4(1+0.7 Sin[800 t])*Sin[10000 t],(2Sin[800 t] +3)},{t,0,0.05},Frame->True]