4 . 1 . 4 Frequency modulation (FM)
By frequency modulation Y-carrier frequency is deviated
in t h e range between the frequencies assigned to sync tip
and white peak. The reasons why Y-signal requires F M are
as follows:
a) F M can transmit D C signal, compress signal band with,
a n d m a k e a r o o m for C-signal.
b) In tape recording system playback output level increases
in proportion to t h e signal frequency a n d decreases
rapidly when the half of the signal wavelength becomes
shorter t h a n the head-gap width. Y-signal is being dis- /*
tributed in the frequency b a n d t o o b r o a d t o be equal
ized effectively. Y-signal equalization t h r o u g h o u t the
. wide frequency range becomes unnecessary by F M .
c) Frequency-demodulated signal level is not affected by
the level fluctuation of F M signal m a d e in transmission
system.
d) F M system makes output signal less affected by the wave
distortion m a d e in the transmission system.
The FMed carrier is then filtered b y High-pass filter ( H P F ) .
Noise level
Type
f p
fc
fa (fdev)
fvt.i
fY(w)
Deviation
Beta
-
688kHz
-
3.6MHz
4.8MHz
1.2MHz
Beta Hi-fi
-
688kHz
L CH = 1.38, 1.53MHz
R CH = 1.68, 1.83
( ± 75kHz)
4.0MHz
5.2MHz
1.2MHz
Super Beta
(HiFi)
-
688kHz
L CH = 1.38, 1.53MHz
R CH = 1.68, 1.83MHz
( ± 75kHz)
4.4MHz
5.6MHz
1.2MHz
VHS (HiFi)
-
629kHz
L CH = 1.3MHz
R CH = 1.7MHz
(± 150kHz)
3.4MHz
4.4MHz
1MHz
8mm VCR
102, 118,
149, 165kHz
743kHz
1.5MHz
( ± 150kHz)
4.2MHz
5.4MHz
1.2MHz
Table 5 Frequency Allocation (NTSC)
4 . 1 . 5 Automatic chrominance control (ACC)
T h e level of C-signal is m a d e constant here.
4 . 1 . 6 Chroma sideband emphasis (8mm VCR only)
8 m m VCR improves the S / N of the reproduced C-signal
by varying the a m o u n t of sideband emphasis nonlinearly
in accordance with the color input level.
4
. 1 . 7
Burst emphasis
Burst emphasis circuit amplifies only the burst signal. This
improves the S / N of the color burst signal.
Color burst signal: A noncontinuous signal bearing a refer
ence phase for the 3.58MHz (4.43MHz P A L ) oscillator.
Color information is in the phase difference between the
reference signal and the modulated carrier.
Refer to Fig. 3, p-17.
37
(3 Hi-fi
Fig. 16 Frequency Allocation
(dB)
Relativ
e
Outpu
t
•Video bandwidth-
Audio bandwidth
Masked by noise
Fig. 17 Magnetic Recording/Playback
Frequency Characteristic
Frequency
