Pioneer tuning fork Service Manual page 47

1 1 . 5 PICTURE SEARCH
In S E A R C H mode, heads cross many 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.
To 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
RFSWP
Envelope
Det.
Envelope
Det.
fc) Head-selecting circuit
Top view
T o v i d e o
Processor
RFSWP
To video
processor
TF/F DOC
Fig. 3 2 Picture Search
Noise bars
AGCed
e n v e l o p e
(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, and 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 taken out while they are
high in amplitude. Fig. (c) shows two examples of their
switching circuit block diagrams.
RFSWP
Output of
A & B heads
Head A
Output of
A ' & B' heads
Head A'
Combined
envelope
A / B ' , B/A'
selector
(d) Switching A/B', B/A' heads
Head B
Head B'
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