Pulse modulation
consists of switching
the carrier on and off
as required.
Fig.1 shows a continuous
wave carrier (CW).
Fig.2 shows the carrier
being switched on for a
short time to produce a
pulse of R.F.
This is the principle of
Radar; a short pulse is
transmitted and then an
echo listened for.
Fig.3 shows a long pulse
and three short ones.
This generates the
letter B in Morse Code.
Fig.4 shows Pulse Width
Modulation (PWM).
The width of the pulse
is determined by the
amplitude of the
modulating signal at
that instant.
Fig. 5 shows Pulse
Position Modulation
(PPM).
Here the width and
amplitude of the pulse
are constant but its
position is determined
by the amplitude of the
modulating signal.
PULSE CODE MODULATION is
where the amplitude of
the modulation is
measured at regular
intervals and a binary
number generated to
represent that
amplitude.
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