Pioneer tuning fork Service Manual page 39

4 . 1 . 4 Frequency modulation (FM)
By frequency modulation Y-carrier frequency is deviated
in the range between the frequencies assigned to sync tip
and white peak. The reasons why Y-signal requires FM are
as follows:
a) F M can transmit D C signal, compress signal band with,
a n d m a k e a room for C-signal.
b) In tape recording system playback output level increases
in proportion to the signal frequency and decreases
rapidly when the half of the signal wavelength becomes
shorter t h a n the head-gap width. Y-signal is being dis- /*
Type
f p
-
Beta 688kHz
-
Beta Hi-fi 688kHz
Super Beta
-
688kHz
(HiFi)
-
VHS (HiFi) 629kHz
102, 118,
8mm VCR
743kHz
149, 165kHz
Table 5 Frequency Allocation (NTSC)
4.1.5 Automatic chrominance control (ACC)
The level of C-signal is made constant here.
4.1.6 Chroma sideband emphasis (8mm VCR only)
8mm VCR improves the S / N of the reproduced C-signal
by varying the amount of sideband emphasis nonlinearly
in accordance with the color input level.
(3 Hi-fi
Fig. 16 Frequency Allocation
fc fa (fdev) fvt.i
-
3.6MHz
L CH = 1.38, 1.53MHz
R CH = 1.68, 1.83 4.0MHz
( ± 75kHz)
L CH = 1.38, 1.53MHz
R CH = 1.68, 1.83MHz 4.4MHz
( ± 75kHz)
L CH = 1.3MHz
R CH = 1.7MHz 3.4MHz
(± 150kHz)
1.5MHz
4.2MHz
( ± 150kHz)
tributed in the frequency b a n d too broad to be equal­
ized effectively. Y-signal equalization throughout 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 made in transmission
system.
d) F M system makes output signal less affected by the wave
distortion made in the transmission system.
The FMed carrier is then filtered b y High-pass filter (HPF).
(dB)
Fig. 17 Magnetic Recording/Playback
Frequency Characteristic
Deviation
fY(w)
4.8MHz 1.2MHz
5.2MHz 1.2MHz
5.6MHz 1.2MHz
1MHz
4.4MHz
5.4MHz 1.2MHz
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.
•Video bandwidth-
Audio bandwidth
Noise level
Masked by noise
Frequency
37