1 4 . 2 V H S Hi-fi
VHS Hi-fi system employs two additional audio heads with
an azimuth of + 30° or - 30° o n t h e d r u m as shown in
Fig. 35. After F M audio signals of 1.3MHz a n d 1.7MHz
are recorded deeply, video signals are recorded shallowly
by ± 6 ° video heads. T h e audio heads with a wide gap can
make a large magnetic field a n d record signals deeply in
the tape while the video heads with a n a r r o w gap can n o t
make a large "magnetic field nor record signals deeply. T h e
level of the reproduced audio signal is high enough despite
of spacing loss which is caused b y video signal recorded
on t h e surface. A l t h o u g h the audio carriers' frequency
ranges are included in that of video carrier as shown in
Fig. (a), cross-talk can be suppressed by a large azimuth
difference of ± 3 0 ° a n d ± 6 ° .
Y signal -
C signal -
Audio -
FM
modulation
Down-
conversion
FM de
modulation
CH1 video(+6°)
CH audio(+30°)
Mixer
629kHz
3.4MHz 4.4MHz
FM audio
(±150kHz)
1.3 1.7 MHz
L R CH
(c)
V H S
Fig. 3 5 Recording System of VHS Hi-fi- VCR
1 5 .
8 m m
Y C R
Fig. 36 and Table 1 show the 8mm video tape format. T h e
top track is for auxiliary functions. T h e b o t t o m track is
for analog audio (1-channel option). T h e diagonal tracks
are for video, F M a u d i o (1-ch), P C M audio (2-ch option)
and tracking pilot signals.
a. Standard recording format
The format has been determined t o m a k e mechanism a n d
ICs compatible t o N T S C a n d P A L . S E C A M signal will
be converted t o P A L before recording. In addition t o t h e
devices of 1/2 " V C R 8mm VCR has employed metal tape
and achieved a high picture quality.
Tape motion
Aux. track for cue
^ T P S ; Tracking Pilot Signal
Fig. 3 6 Track Pattern of 8mm V C Tape
MHz
47
c
0.629
A(L)
A(R)
Y
1.3
1.7
(MHz)
Video
signal
A u d i o
signal
Y
C
A(L)
A(R)
Head
direction
CH2 video(-6°)
CH2 audio(-30°)
C signal
Y signal
wmsm
Audio head
Reference edge of tape
Aux. track for audio
Video • FM audio
+ TPS
PCM audio + TPS
Pilot signals
C
Y
Recordin
g
leve
l
Fig. 3 7 Frequency Spectrum of 8mm VCR
; 10°
CH-1
10°
CH-2
