Grf-1300a user manual and teaching materials, Unmodulated state) to an am wave (modulated state), Ω) and (ω – GW Instek GRF-1300A User Manual
Page 64: Ω) are included. one is higher than ω
GRF-1300A User Manual and Teaching Materials
(unmodulated state) to an AM wave (modulated state).
Figure 5-1. A
diagram showing
how an
unmodulated
carrier signal
undergoes the
process of
modulation.
Figure 5-2. AM
waveform in the
time domain and
the frequency
domain
m
U
Ω
t
t
t
cm
U
( )
AM
U
t
cm
U
c
−
ω
ω
ω Ω
c
ω + Ω
2
a
m
Ucm
2
a
m
Ucm
2. AM Wave Spectrum
Expand formula (4.3) to get the following formula:
1
1
( )
cos
cos(
)
cos(
)
2
2
AM
cm
c
a
cm
c
a
cm
c
u t
U
t
m U
t
m U
t
−
=
ω +
ω + Ω +
ω Ω
As can be seen here, a
single modulated audio signal consists of three high frequency
components. In addition to the carrier, two new frequency
components (ω
c
+Ω) and (ω
c
- Ω) are included. One is higher than
ω
c
, known as the upper sideband, and the other is lower than ω
c
,
known as the lower sideband. Its spectrum is shown in Figure 5-
3.
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