Upper-cylinder
Video-head
Rotary
transformer •
FG-pattern-
Magnet'
Lower-drums of aluminum alloy are processed in a weather
chamber in the accuracy of submicron order. The Lower-
d r u m has a rail to guide the t a p e helically. T h e angle a n d
linearity of the rail determines t h e tape track p a t t e r n . T h e
heads are m o u n t e d on the d r u m or disc so t h a t their faces
protrude out of the drum face by 30/im to 50/mi. The align
ment of the heads have precisely been m a d e in factory.
Driving-motor (generally 3-phase) and Rotation-senser (FG
& P G ) are also very accurate t o minimize jitter or time-
base error. Video signal is highly affected by jitter. R o t a r y
head is superior t h a n stationary head in minimizing jitter.
Core
B-ch coil
- Lower-
cylinder
A-ch coil
Coil
Rotary core
Fig. 3 Rotary Transformer (Electric signal coupler)
Fig. 2 Drum (cylinder)
1 . 3 Video Head
1.3.1 Material
The requirements to video head material are the same as
those to audio head material. M n - Z n ferrite a m o n g mag
netic oxides, and permalloy and sendust a m o n g nonoxides
are suitable for the head. H o m e VCRs employ hard-
wearing and highly permeable M n - Z n ferrite. Sendust and
a m o r p h o u s heads of high saturation flux density will be
employed in the near future. The characteristics of sen
dust and ferrite heads obtainable when a metal tape is
played back are shown in Fig. 4.
1.3.2 Structure of video-head
The structure of Video head is simple. Its coil has tens of
turns. T h e n a r r o w p o r t i o n of the head-top is protected by
glass as seen in Fig. 5. T h e head is fixed on a head-base
and is m o u n t e d on the U p p e r - d r u m or Rotary-disc in be
tween the d r u m s . The head deals with the signals of short
wavelength having a very narrow g a p . The length and
width of the head-gap determine the recording/playback
performance.
Fig. 4 Playback Characteristics of Sendust and Ferrite
Head
Core
Coil
Coil
31
1.2 Drum ( c y l i n d e r ) S c a n n e r
T h e Scanner consists of a stationary Lower-drum, a rotary
U p p e r - d r u m equipped with two R E C / P B - v i d e o - h e a d s
diametrically opposite each other, a Drum-motor for turn
ing the U p p e r - d r u m , a n d a Rotary-transformer for elec
trically coupling the heads with signal processor. In /5
V C R s , U p p e r - d r u m is also stationary and the heads are
m o u n t e d o n a Rotary-disc inserted between the drums. In
8 m m VCR, U p p e r - d r u m rotates. The rotary heads and
d r u m driving mechanism are the most important for pick
ing up recorded information correctly. The Upper- and -
Shaft
Grounding-brush
Hall
element
PG magnet
Coil
Gap
Stationary
core
P
B
outpu
t (mV
)
Sendust head
Ferrite head
Metal tape
5.8m/s
35/zm w i d t h
(MHz)
Gap
Glass
Gap
Core
(b) Video head
(a) Audio head
Fig. 5 Audio and Video Heads
