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Wire and Wireless Communication Applications Chap. 8
m B (t)—are needed to drive the circuits that create the red, green, and blue light.
Furthermore, a compatible color TV transmission system is needed such that black-andwhite
TV sets will receive the luminance video signal, m y (t), which corresponds to the gray
scale of the scene. This compatibility between color and black-and-white transmission is
accomplished by using a multiplexing technique analogous to that of FM stereo, except that
three signals are involved in the problem instead of two.
The National Television System Committee (NTSC) compatible color TV system that
was developed in the United States and adopted for U.S. transmissions in 1954 will be discussed.
This technique is illustrated in Fig. 8–34. To accomplish compatible transmission,
the waveforms that correspond to the intensity of the red, green, and blue components of
the scene—m R (t), m G (t), and m B (t), respectively—are linearly combined to synthesize the
equivalent black-and-white signal, m y (t), and two other independent video signals, called the
in-phase and quadrature components, m i (t) and m q (t). (The names of these components arise
Color camera
Red filter
Camera
Green filter
Camera
Blue filter
Camera
m R (t)
m G (t)
m B (t)
Matrix
M
cos(v c t + 33°)
3.58 MHz oscillator
m y (m)
m q (m)
m i (m)
90°
phase shift
Sync
Electronic
switch
Sync
generator
Blanking
Baseband
composite video
(5-MHz bandwidth)
m c (m)
To TV
transmitter
baseband
modulation
input
Sync
Sync
waveform
Front
porch
3.58-MHz burst
(8 cycles minimum)
Back porch
10.5 msec
Blanking
63.5 msec
Horizontal sweep interval
10.5 msec
t
Figure 8–34 Generation of the composite NTSC baseband video signal.
[Technically, m q (t) is low-pass filtered to an 0.5-MHz bandwidth and m i (t)
is low-pass filtered to a 1.5-MHz bandwidth.]