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While the CH-1 track component is recorded with phase un-
changed, the phase of the CH-2 track component is delayed
90° every line. Fig. 1-10 illustrates the principle of this
phase shift system,
Head travel rotation
WZ
et
[vs
"
ASR
(a) REC tracks
Bf
fers fara [ara oe Pe
oa] AR ALAA |S
A
6
OE IX
Cree
C e e
ora
Signal
JINIZIN
AZ
(b) PB CH-1 track
vas
[aoa [ae aI [ava [west
Crosstalk
ilies
}
(CH-2)
LAS
| A
oe
Cre
re
{c) 2H delay
211 delayed.
i
line out
ae
ZINIZIN
|Z
TA
[THE [eae [THT TS
2H delayed |
fe
crosstalk
| 7 | |
|
A
i
sional
(ony
(d) PB color out
without
crosstalk
Fig. 1-10
Phase shift system
In the figure, (a) indicates the phase shifted recording pat-
tern. Since the CH-1 head pattern is not phase shifted, the
R-Y component
phase becomes
inverted every
line. The
phase of the CH-2 head pattern is delayed every line and
this causes its R-Y component
phase to become
inverted
every two lines.
During playback, when the CH-1 head picks up a portion of
the CH-2 track signal, this becomes the crosstalk component.
Phase shift is not required for the main signal from the CH-1
track, and this output is shown by (b). The dotted arrows
indicate the crosstalk component and, as can be noted, the
phase reverses every 2 lines.
Passing signal (b) through a 2H delay line yields signal (c).
In comparing signals (b) and (c), the main signal phase is
the same every line, but the crosstalk phase reverses. There-
fore, by mixing signals (b) and (c), the crosstalk component
of the adjacent track can be removed to result in the play-
back color signal (d).
In other words, the color signal can be considered in 2H
units. It is recorded
by the phase shift system and during
playback, the signal through a 2H delay line is mixed to
remove crosstalk.
Crosstalk in the playback color signal (d) effectively be-
comes zero, while the main signal is enhanced to improve
S/N. Also, the CH-2 head playback phase is advanced 90°
every
line
(opposite
to recording),
produring
the same
effect. A digital type system is used for phase shifting.
1.5.2
Down Converted Color Subcarrier Frequency
The color subcarrier frequency (Fs) can be expressed as:
Fs =(n—1/4)Fh + 1/625 Fh = 283.75 Fh + 25 Hz (n= 284)
= 4.433619 MHz
A line offset system is used in which the subcarrier phase is
delayed 90° every line. This avoids serious color noise when
the color signal is displayed on a monochrome TV receiver.
25 Hz is added in order to prevent crosscolor.
As indicated in Fig. 1-10, the phase of the color signal R-Y
component
is inverted every horizontal line to compose a
synchronous quadrature modulated signal. Fig. 1-11 shows
this color signal spectrum.
14 Fh
AN
AN
A
:
JN
I
VIR
UK,
Luminance
27}
ENE
EN
TN
signal
"282 Fh
283Fh
—|284Fh
«BSH
286 Fh
t
fi
i
Color signal
(R-Y) main energy —~
N1R-Y) main energy
(B-Y) main eneray
(Fs; subcarrier)
Fig. 1-11
Spectrum of color signal
In the phase shift system, the CH-1 component of the down
converted color signal is distributed at 1/2 Fh intervals
centered on the Fe (down converted color subcarrier) com-
ponent. The CH-2 track component is delayed in phase 90°
every line, deviated by 1/4 Fh, and distributed at 1/2 Fh
intervals centered
on Fc. This spectrum
is shown
in Fig.
1-12,
Fe (Down converted color
subcarrier frequency)
H
(CH+ track
(BY)
'components
(RY)
CH2 track
components
Fig. 1-12
Spectrum of down converted color signal
17
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