T o find out the polarity of the m o d u l a t i o n axis of
(ER-EY), burst signal phase is shifted by 90° every line.
If t h e chrominance subcarrier frequency (Fc) is made a half
of t h e horizontal scanning frequency multiplied by an odd
n u m b e r as in N T S C system, the (R - Y) component will
be in phase between the adjacent scanning lines, and ver
tical stripes will appear. The chrominance carrier frequen
cy, therefore, is determined by t h e following equation: /
fc = (284-1/4) X f
H
+ (f
H
/625) = 4.4336 MHz
Provided: f
H
= 15,625 Hz
Thus the color carrier energy is interleaved in luminance
signal spectrum fo/4 out of p h a s e from it. T o m a k e the
dots invisible in 625-line system, 25Hz (fu/625) is a d d e d .
Fig. 6 shows the waveforms of N T S C and P A L video sig
nals during the field blanking period.
1st field
Pedestal level
_Equalizing _
pulses
Vertical retrace blanking period
End of the last (bottom)
horizontal scanning
line in the 2nd field
Beginning of the 1st (top),
line of the 1st field
Video carrier null level
End of the 1st field
Beginning of the
2nd field
Video carrier null level
Picture information
A.
NTSC
SIGNAL IN THE
1st
AND 2 N D FIELDS
Field sync
datum line
a-
Burst blanking : 1st Field
Burst blanking : 2nd Field
Burst blanking : 3rd Field
Burst blanking :
4TH
Field
Burst phase
135° ('NTSC-lines')
Burst phase
225° ('PAL-lines')
Fig. 6 Video signal waveforms during the field blanking period
S E C A M
SYSTEM
In the S E C A M system the sub-carrier is frequency
m o d u l a t e d by (R - Y) on one line a n d (B - Y) on the next
instead of being m o d u l a t e d by the two color difference
signals simultaneously. Details are omitted here because
we are not manufacturing video equipment of this type at
the m o m e n t .
15
Black level
White level
2nd field
Equalizing
pulses
Vertical sync
pulses
Horizontal sync
pulses
4th Field
1st Field
2nd Field
3rd Field
b. 625-line PAL video signal
