(b) Pilot frequency (NTSC)
A c h
Bch
LPF
46kHz BPF
16kHz BPF
Too fast
(/
3
~ /
4
)
Tracking error
CO Tracking Servo Circuit
Fig. 3 9 Automatic Track Finding(ATF)
d. Flying-erase-head
In the (3 a n d V H S systems one frame erasing is impossible
because the fixed Full-erase-head erases the signal across
the full tape width. This produces noise signal when edit
ing. In 8mm V C R an Erase-head installed between the two
Video-heads on the D r u m can erase signals frame by frame
with the help of the A T F system. This makes noise-free
editing possible.
49
Tape
Video
PCM
Head
Pilot signal
shifts here
(a) When tape is slow.
2 /
H
46.145kHz
16.407kHz
46.259kHz
16.521kHz
A /
A
« / „
A /
B
- 3 /
H
f
H
X integer
/
1
-102.544kHz-(378/
H
)/58«-CH1
/
2
-118.951kHz-(378/
H
)/50-CH2
/
3
=165.210kHz-(378/
H
)/36 - CH3
/
4
=148.689kHz-(378/
H
)/40 - CH4
l
P
/ l
c
- - 1 4 d B
(375/
H
in PAL)
RFSWP
Center pilot is neglected.
( / 1 + / 2 + / 3 )
( / 1 ~ /
4
)
Too slow
Pilot OSC
(A)
Capstan motor
+
Reference pilot to be added
Full-erase head
•Tape
Erased
area
Head
(a) Full erase
Flying-erase head
(b) Flying erase
Fig. 4 0 Erasing Methods
