Pioneer tuning fork Service Manual page 36

When recording, the video signal is applied to both A- and
B-heads. In playback, the picked-up signals coming from
A - and B-heads are alternately switched to make one con­
tinuous signal channel as shown in Fig. 10. T o make one
track surely contain one full field information, the tape
wraps the head drum a little longer t h a n 1/2 turn. When
Overlap
Track B
Track A
Switching points
Control track
Viewed f r o m video head
•1V-
CH-1 input
CH-2 input
Switching pulses
CH-1 output
CH-2 output
Added
Fig. 10 Connecting CH1 and CH2 signals
with a Switching Circuit
34
Noise
Overlap
1 frame
1 frame
connecting the two signal, switching noise is generated. To
avoid this, the connection is performed about 7 H before
V-sync appears or at the bottom of the screen where the
A- and B-tracks overlap each other. The heads rotates at
l,800rpm to produce 30 frames (1500rpm, 25 frames in
P A L ) of pictures a second.
Audio track
V-sync
Switching point
Overlap
Fig. 11 Field and Frame
1H
Field A
(track A)
Field B
(track B)
1 frame