NTSC
SYSTEM
O u r eyes are sensitive to orange and cyan on small spots
and not so sensitive to magenta and green. W h e n a colored
thing becomes small, its color approaches orange or cyan.
T h e color becomes insensible when a colored spot becomes
smaller. So, a wider frequency range (1.5MHz) has been
allocated t o the orange-cyan information t h a n to Green-
Magenta information (0.5MHZ) in N T S C color TV format.
All colors can be m a d e by mixing red (R), blue (B) and
green (G) light. They can also be m a d e of ( R - Y ) and
( B - Y ) signals.*
*R, G, B and Y stand for red, green, blue and luminance
signals. Y-signal is made up of 0.3R + 0.59G + 0.1 IB and
produces monochrome pictures.
Color signal is carried by I and Q signals, which are on
the axes advanced by 33° from ( R - Y ) a n d ( B - Y ) axes
respectively in the phasor diagram shown in Fig 1. They
are out of phase each other by 9 0 ° .
E I
and E
Q
signals are
m a d e by the following equations:
Ei = 0.74 (E
r
-Ey) - 0.27 (E
B
-E
Y
)
E
Q
= 0.48 (E
r
-Ey) + 0.41 (E
B
~E
Y
)
TV receiver reproduces ( E
R
- E
Y
) and ( E
B
-
E
Y
)
signals in
stead of reproducing
E I
and E
Q
with a simplified color cir
cuit which has only 0
. 5 M H Z
b a n d w i d t h because it is
practically unnecessary t o reproduce Ei and E
Q
t h r o u g h
out the frequency range of 1
. 5 M H Z
being b r o a d c a s t .
T o m a k e the broadcast signal compatible to m o n o c h r o m e
and color TV receivers, chrominance signal is being
inserted into the vacant spaces of luminance signal in the
frequency spectrum as shown in Fig. 2.
W h e n a colored p r o g r a m is reproduced on a m o n o c h r o m e
receiver, white dots m a y appear due to the beating between
picture carrier and color carrier as shown in Fig. 3. These
dots have been minimized by determining the chrominance
subcarrier frequency at a half of the horizontal scanning
frequency multiplied by a n odd n u m b e r .
fs = fff/2 X 455 = 3.579545 (MHz)
f
H
: Horizontal scanning frequency, 15.734 Hz
+ U axis (PAL) 0°
Fig. 1 l/Q (NTSC) and V / U (PAL) Quadrature
Components of a Vector
Fig. 2 Spectral Distribution of the TV Signal
Brightness reverses in the n e x t f r a m e .
Fig. 3 Color Carrier Interference Reduced by Interleaving
13
- U axis 180°
Luminance signal
Chrominance signal
Odd multiple of
fh
/2 (117)
Odd multiple of
fh/2
(455)
Integral multiple of//? (286)
4.5 MHz
Luminance signal
Chrominance signal
Video carrier
fp
Chrominance signal
subcarrier/s
Sound carrier
fa
fp
fs
Q
I
Bright
Dark
1/3.58
jus
1st scanning line
2nd scanning line
3rd scanning line
4th scanning line
Bright parts
Dark parts
Brightness reverses on the next line.
