Akai VS-2EGN

9-2 VIDEO MODULATOR
BIAS
CIRCUIT
VIDEO/AUDIO
INPUT
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Fig. 7-118 Video Modulator
In Fig. 7-118 the modulating circuit is enclosed in a
broken line. This circuit is a balanced modulator. If the
voltage applied from the bias circuit and the video input
signal voltage are at the same level, the RF carrier output
BIAS becomes zero. If they differ, the carrier output is pro-
VOLTAGE portional to the level difference.
In Fig. 7-119, the degree of modulation (M) is Tene
As the bias voltage changes, the degree of modulation
changes. (The degree of modulation can be changed by
: changing VR1).
Fig. 7-119 jn Fig. 7-118, C14 is for matching the impedance viewed
from the input side. The pi(m) type attenuator (R9-11)
is for adjusting the RF output level, and serves as a buf-
fer for the modulator,
9-3 CARRIER OSCILLATOR
K)
cSt
c L
OO
Fig. 7-121 Carrier OSC equivalent circuit
Fig. 7-120 Carrier Oscillator circuit
1 ‘ ; 3
Fig. 7-120 shows the carrier OSC circuit. Fig. 7-121 is 2m LG” © TePresentsa variable capacitor, and it can
the equivalent circuit. Fig. 7-121 shows a collector tun- change the channel by changing its position in the fre-
ing type OSC circuit. Oscillation frequency (fc) is fo= quency spectrum.
Service Manual VS-2EGN
82