1 1 . 5 PICTURE S E A R C H
In S E A R C H m o d e , heads cross m a n y tracks and repro
duce many noise bars as shown in Fig. (b).
As mentioned, 2-head VCR produces noise while the A
head is sliding on B-tracks and the B-head is o n A-tracks.
T o suppress the level variation and noise bars Automatic
Gain Control (AGC) circuit smoothes the envelope peaks
as shown in Fig. (b) b o t t o m .
Track width
(a) Double-azimuth head
(b) Picture search
4-head VCR can pick u p B-track signal with the B ' - h e a d
when A-head is on a B-track, a n d A-track signal with the
A ' - h e a d when the B-head is on a A-track. The signals
reproduced by the heads are quickly switched between A-
B ' and B - A ' and are alternately t a k e n out while they are
high in amplitude. Fig. (c) shows two examples of their
switching circuit block diagrams.
RFSWP
O u t p u t of
A ' & B ' heads
To video
processor
Combined
envelope
A / B ' , B / A '
selector
fc) Head-selecting circuit
(d) Switching A/B', B/A' heads
Fig. 3 2 Picture Search
45
Noise bars
AGCed
e n v e l o p e
Top v i e w
RFSWP
Envelope
Det.
Envelope
Det.
RFSWP
TF/F
DOC
T o v i d e o
Processor
O u t p u t of
A & B heads
Head A
Head B
Head A'
Head B'
