Pioneer tuning fork Service Manual page 49

1 4 . 2 V H S Hi-fi
VHS Hi-fi system employs two additional audio heads with
an azimuth of + 30° or - 30° on the 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. The audio heads with a wide gap can
make a large magnetic field and record signals deeply in
the tape while the video heads with a narrow 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 by video signal recorded
on t h e surface. Although 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 ° .
FM
Y signal -
modulation
Down-
C signal -
conversion
FM de­
Audio -
modulation
8mm
1 5 . Y C R
Fig. 36 and Table 1 show the 8mm video tape format. The
top track is for auxiliary functions. T h e b o t t o m track is
for analog audio (1-channel option). The diagonal tracks
are for video, F M audio (1-ch), P C M audio (2-ch option)
and tracking pilot signals.
a. Standard recording format
The format has been determined t o make mechanism and
ICs compatible t o N T S C and P A L . S E C A M signal will
be converted t o P A L before recording. In addition to the
devices of 1/2 " V C R 8mm VCR has employed metal tape
and achieved a high picture quality.
CH1 video(+6°)
CH audio(+30°)
Mixer
CH2 audio(-30°)
Fig. 3 5 Recording System of VHS Hi-fi- VCR
Pilot signals
C
Fig. 3 7 Frequency Spectrum of 8mm VCR
c
0.629
Video
signal
C signal
629kHz
CH2 video(-6°)
FM audio
(±150kHz)
1.3 1.7 MHz
L R CH
(c)
V H S
wmsm
Video • FM audio
+ TPS
PCM audio + TPS
Audio head
^ T P S ; Tracking Pilot Signal
Fig. 3 6 Track Pattern of 8mm V C Tape
Y
A(L)
Y
A(R)
1.3 1.7 (MHz)
Y A(L)
A u d i o
C
A(R)
signal
Y signal
3.4MHz 4.4MHz
Tape motion
Aux. track for cue
; 10°
CH-1
10°
CH-2
Aux. track for audio
Reference edge of tape
MHz
Head
direction
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