2-61
In communications PULSE-MODULATION SYSTEMS, the modulating wave must be
SAMPLED at 2.5 times the highest modulating frequency to ensure accuracy.
PULSE-AMPLITUDE MODULATION (pam) is modulation in which the amplitude of each pulse
is controlled by the instantaneous amplitude of the modulation signal at the time of each pulse.
PULSE-DURATION MODULATION (pdm) or PULSE-WIDTH MODULATION (pwm) are
both designations for a type of modulation. The width of each pulse in a train is made proportional to the
instantaneous value of the modulating signal at the instant of the pulse.
PULSE-POSITION MODULATION (ppm) has the advantage of requiring constant transmitter
power. The amplitude and width of the pulses are kept constant. At the same time, the position of each
pulse, in relation to the position of a recurrent reference pulse, is varied by each instantaneous sampled
value of the modulating wave.
