Pioneer tuning fork Service Manual page 15

NTSC
SYSTEM
O u r eyes are sensitive to orange and cyan on small spots
and not so sensitive to magenta and green. When a colored
thing becomes small, its color approaches orange or cyan.
The color becomes insensible when a colored spot becomes
smaller. So, a wider frequency range (1.5MHz) has been
allocated to the orange-cyan information t h a n to Green-
Magenta information (0.5MHZ) in NTSC color TV format.
All colors can be made 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
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 ) and ( B - Y ) axes
respectively in the phasor diagram shown in Fig 1. They
are out of phase each other by 90°. E I and E
m a d e by the following equations:
- U axis 180°
Fig. 1 l/Q (NTSC) and V/U (PAL) Quadrature
Components of a Vector
Bright
Dark
Brightness reverses in the n e x t f r a m e .
luminance
signals are
Q
+U axis (PAL) 0°
1/3.58 jus
Fig. 3 Color Carrier Interference Reduced by Interleaving
Ei = 0.74 (E -Ey) - 0.27
r
E = 0.48 (E -Ey) + 0.41
Q r
TV receiver reproduces ( E
R
stead of reproducing E I and EQ with a simplified color cir­
cuit which has only 0 . 5 M H Z bandwidth because it is
practically unnecessary to reproduce Ei and EQ through­
out the frequency range of 1 . 5 M H Z being broadcast.
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.
When a colored program is reproduced on a m o n o c h r o m e
receiver, white dots may 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 an odd number.
fs = fff/2 X 455 = 3.579545
f : Horizontal scanning frequency,
H
Luminance signal
Chrominance signal
I
fp
Odd multiple of fh/2 (455)
Integral multiple of//? (286)
4.5 MHz
Luminance signal
Chrominance signal
Video carrier fp
Chrominance signal
subcarrier/s
Fig. 2 Spectral Distribution of the TV Signal
1st scanning line
2nd scanning line
3rd scanning line
4th scanning line
Bright parts
Brightness reverses on the next line.
(E -E )
B Y
(E ~E )
B Y
- E ) signals in­
- E ) and ( E
Y
Y B
(MHz)
15.734 Hz
Q
fs
Odd multiple of
fh/2 (117)
Sound carrier fa
Dark parts
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