Pulse Amplitude
Modulation
Cuthbert Nyack
This type of modulation is used as the first step in converting an
analog signal to a discrete signal or in cases where it may be
difficult to change the frequency or phase of the carrier.
In this case the carrier is a pulse train rather than a sine
wave and the spectrum of the carrier consists of several components
at nwc =
2np/T where T is the time between pulses.
The applet below shows
a PAM signal and how it varies with modulating signal amplitude
and frequency. The spectrum of the PAM signal is shown at the top
in black. In this case each component of the carrier's spectrum has
become an AM spectrum. Notice that the spectrum contains a component
at the modulating frequency which makes the PAM signal relatively easy to
demodulate.
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COPYRIGHT © 1996 Cuthbert Nyack.