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® Frequency Synthesizer Section (LW)
The
LW
section
employs
a
direct
frequency
dividing
method.
So that the reception frequency is incremented in
1 kHz, the frequency
of the phase comparator
is 1 kHz.
This is produced by dividing 4.5 MHz
(the output of X2),
which is a clock frequency of IC7, into 1/4500.
Since the reception frequency range is 153 ~ 281 kHz and
the intermediate frequency is selected at 450 kHz, the fre-
quency of the local oscillator (VCO) is 603 ~ 731 kHz. This
output
is output from pin 12 of IC5
and enters pin 9 of
IC7.
IF
the
frequency
dividing
ratio
of the
programmable
counter
jin IC7 is set to 603 ~ 731, the output frequency
is 1 kHz.
This
is compared
in phase with a reference fre-
quency
of 1 kHz
by the phase comparator
and is output
from
pin 11 of IC7. The output signal is converted into a
DC voltage signal by the loop filter consisting of Q22 and
Q23, which
in turn controls the tuning circuit as a tuning
voltage.
<-] => Celery 4
LW
TUNING
VOLTAGE
Loop Filter
12
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