Amplitude Modulation, Nonlinear Modulator.
One of the easiest ways to produce an AM signal is by the
product modulator. Here the 2 signals
(1 + m cos(wm t) and
cos(wc t) are multiplied together
to produe an AM signal.
Another method is by using a nonlinear circuit. One
possibility is shown in the applet below where a circuit
with chracteristics vo(t) = vi(t) + m/2 vi(t)2 is used.
The applet below shows how an amplitude modulated signal can
be produced by a nonlinear circuit. vi(t) is in Yellow
and vo(t) in Red and Green. The output has
components at 0, wm,
wc - wm,
wc + wm,
The Green curve shows what happens when the frequencies other
than wc - wm,
wc + wm are removed.
In practice this would be done by a resonant circuit,
coupled resonant circuits or other band pass filter.
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COPYRIGHT © 2008 Cuthbert Nyack.