Pioneer tuning fork Service Manual page 34

1.3.3 Playback characteristic of video-head
In recording and playback, high frequency signal compo­
nents are decreased by spacing loss, core loss, thickness
loss, etc. as seen in Fig. 6. To minimize the loss the head-
gap width should be 1/3 or shorter than the shortest signal /
Thickness loss
+6dB/OCT
(a) Tape head frequency response
2. Video Tape
2 . 1 Structure
There are several kinds of tapes classified by uses; broad­
casting, professional and home uses. Their dimensions and
magnetic materials are different each other. H o m e tapes
are made of G O 2 and CR-FEIOS. Coated metal tape for
8mm video high density recording is now available, and
vacuum-evaporation tape is under development. The coat­
ed tape is basically the same as the audio tape. The back-
coated tape shown in Fig. 7 has a carbon layer on the re­
verse side for minimizing electric resistance and charge and /
2 . 2 Performance of Video Tapes
The following performance is required to video tapes:
a) Low tape-width variation
b) Hard-wearing
c) Less dropouts
d) Optimum friction coefficient
e) High mechanical strength
32
Spacing loss
Core loss
Gap loss
5MHz
Frequency
Fig. 6 High Frequency Compensation by Preamplifier
Magnetic layer
Coating layer
Base
• Coating
Fig. 7 Cross-section of Video Tapes
wavelength. T o make the playback frequency characteris­
tic flat, compensation is made with a resonant circuit con­
sisting of head coils and capacitors and resistors in the
input stage of pre-amplifier.
5MHz
(b) Compensating
for improving winding characteristic. Some have a bind­
ing layer between the magnetic material and base. Vacuum-
evaporation tape is made by evaporating a high retentive
material and depositing it on a base in a vacuum cham­
ber. After that a protective layer of 100A thick is formed
for protecting the material against wear and corrosion.
Pollyester of high Young's modulus and good tempera­
ture characteristic is popularly employed for the base.
Tape
C o - F e 0
7 2 3
Bs (Gauss) 1800
1500
Br (Gauss)
He (Oe) 680
Thickness of
5
magnetic layer
Entire
20
thickness (/^m)
Use 1/2"
Table 4 Specifications of Tapes
- Protector
- Evaporation-deposited
magnetic layer
-Base
Coating
Evaporation-
Metal
deposited
2 0 0 0
2300
*
1500
2.5 0.15-0.2
13 13
8 m m 8 m m