T h e n the brightness of 3.58MHz dots is inverted line by
line and frame by frame and is m a d e insensible. T o avoid
beating interference between the colour and sound carriers,
the horizontal scanning frequency has been determined at
15,734 ( 1 5 , 7 5 0 - 1 6 ) H z .
The transmitting method of composite chrominance signal
by placing its bands of energy between those of luminance /
PAL SYSTEM
N T S C and P A L employ Q . A . M . system of chrominance
signal. They transmit two chrominance information
simultaneously, employ a synchronized detector, and hue
a n d chrominance saturation are determined by phase
difference a n d relative level between the burst signal and
chrominance signal.
There are, however, some differences between t h e m . P A L
uses simple weighted ( R ' - Y ' ) a n d (B' - Y') color-
difference signals of equal bandwidth to modulate the two /
signal is called " i n t e r l e a v i n g " . T h e luminance and carrier
color signals ( E
Y
, E
C
n) are represented by the following
equations:
E
Y
= 0J0E
R
+ 0.59E
G
+ 0.11E
B
ECN = a(E
R
— Ey) cos oost -h b(E
B
— E
Y
)sin
o)St
a: 0.877, b: 0.493, f
s
: 3.58MHz
q u a d r a t u r e phase (but equal frequency) subcarriers while
N T S C system employs complex I a n d Q signals which have
unequal b a n d widths.
T h e most significant difference is in modulating m e t h o d .
P A L ' s m o d u l a t i o n axis of ( E
R
- Ey) inverts every 1H while
that of N T S C does not. The carrier color signal is represent
ed by the following:
ECP = ± Q(ER — EYJc b(Es — E
Y
)sinwst
Fig.
3
Bandwidth of European 625-line System for
Bands IV/V (Channel Width: 8MHz).
P A L receiver adds and subtracts the direct and lH-delayed
signals. Adder and subtractor put out (B - Y) a n d (R - Y)
signals respectively. The demodulated signal becomes an
average between the two adjacent lines. Thus the resolution
becomes a little lower than that of N T S C in principle, and
the modulating circuit becomes complicated. P A L system,
however, has a higher allowance in phase distortion in the
transmission system.
The P A L system nullifies hue error or the phase error of
color signal. If the transmitted signal is m a g e n t a for sever
al scanning lines a n d is subjected to a phase lag of 0 ° , the
vectors of a pair of received lines will be as E l and E2 in
Fig. 5. The even or odd lines inverted by a transmitter are
reinverted by the receiver and the lower line of the pair leads
from the original phase as E 2 \ W h e n E l and E 2 ' are
integrated and averaged visually or electrically, the phase
error is nullified. If the error is large, the integration be
comes difficult and color moves up and down (Hanover bar
or Venetian blind).
Reiverted lower line of a pair
(reddish magenta)
+ V
Received lower line
Fig. 5 Phase Error Correction with the PAL system
14
K,G
l,L
G
I
L,K
MHz
/ c - 4 . 4 3
0.75
1.25
urn
•1.1
1.6-
Burst
Color subcarrier
Burst
n line
E
R
- E
Y
(n+1) line (n+2) line
Fig. 4 PAL's Transmission Vectors
E'2
Ei
Transmitted original hue magenta
Received upper line of a pair
(bluish magenta)
+ U
E2
