Page 130 - Intro to Space Sciences Spacecraft Applications

Communications

BASERAND 117
(INFORMATION)
SIGNAL

CARRIER
WAVE

AMPLITUDE
MODIILATED
SIGNAL

Figure 5-6. Amplitude modulation. The amplitude of the carrier wave is
changed in a way to represent the information to be transmitted.

CARRIER
WAVE

FREQUENCY
MODIIIATED
SIGNAL

Figure 5-7. Frequency modulation. The frequency of the carrier wave is
changed in a way to represent the information to be transmitted.

Phase Modulation (PM)

Information can also be impressed upon a carrier signal by using the
baseband signal to modify the phase of the carrier wave, called phase
modulation. The rate at which the carrier phase is changed, and/or the
location along the wave at which the change occurs, can be used to repre-
sent the baseband signal.
An example of a PM signal is shown in Figure 5-8. Notice, in this case,
that both the amplitude and frequency of the signal remain constant and
that only the phase changes, as indicated by the arrows in the figure. Phase