FFT, Pulse Position Modulation.
A Pulse Position signal with pulse carrier frequency
and sinusoidal modulating frequency w2
and its spectrum is shown below.
This spectrum can have a high harmonic content
eg (8.0, 1.0, 0.006, 12.56, 1024, 0.0, 256, 750.0, 15.0, 0.08)
As the modulating index m is increased, the spectrum does not contain
a component at the modulating frequency and so cannot be demodulated
by a low pass filter unlike PAM and PWM. In fact a low amplitude
component does occur in the applet but this is an artifact arising from how the
PPM signal is generated.
eg parameters (8.0, 1.0, 0.006, 12.56, 1024, 0.15, 256, 750.0, 15.0, 0.08)
As the modulating index is increased, the spectrum changes differently
from a PAM signal because a different set of lines appears around
different harmonics. In fact a PM spectrum appears around each
harmonic with the modulating index increasing with harmonic number.
The spectra around the higher harmonics therefore spreads out much
faster than the spectra around the lower harmonics as m is increased.
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COPYRIGHT © 2007 Cuthbert Nyack.