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TX·7430
4. PLL tuned circuit
26
I
r-
sc
A
block diagram of the tuned of the
PLL
is
shown
in
the
above
diagram.
Operation during AM reception
The reception frequency
is
applied to the
p
ro gr arn
ma
ble
d
iv id e r
wnere
it is
divi
ded
t
o lI
N and
outpur
as
fv
.
This
is
applied
to the phase
cornpar
aror
w
here
it is
cornparated
w
ith frequenc
y
reference fr (9k H z fo r
G/W
model
s a
nd
10kHz for D rn
od el l . If
fr and fv d
iffer .
E
o
equal t
o
the
difference in
Ireq uency
is
output.Since
err
or
o
u t p u r
E
o
is
a pulse waveforrn
.
it is passed
t
hr ough the
low
pass
filter
t
o change it into
oe
volt age Vd , which is applied
to the variable capacitor diode in the front en
d
to change
the reception frequenc
y .
Thi
s
continues unt il
fv
and fr are
the
sarne
and Eo·O
.
Operation du r in g FM reception
The pulse
swallow
method is
used in the
pr
escaler
of thi
s
unit
.
In th
is
t
ype o
f
prescaler .
a
supple rne nt
ary number
5. Auto search tuning circuit
TONED
INDICATOR
Q103
8
+B
FM IF&AM
cc
w
SY
STEM
-.J
07
03
-.J
12
22N
0
TO
P
OCC
STEREO
r-
f-
DECODER
06
u
Q
1 13
D10 7
NOI SE
1""1
DETECTOR
(chan
ged
acc
ordirng
to the program code input) and the
divided rec ept
ion
frequency from the
presca
ler are
combined in the c
ontro!
c
ounter
an
d
the
presca
ler'
s
divi
sion Iac
ro r
is swit ch ed
1/16
o
r 1/!7
ac
co rd ing
to
ex
ternal
co
n tro l
(I/!6
w
he n th
e
PSC
t
erminal is
"H
"
and
1/17
w
he n
it
is
"
L " ).
The
st
at ion
osc
illat
o
r frequenc
y is
app
lied
t
o
the
program
m
able
d
iv ider .
but the pr ograrnm
abl e
d
ivider
has an upper
frequenc
y
limit
o
f only 30MHz.
so
the pulse
swallow-type
pr
escaler
i
which can
be
used up to ISOMHz.is
insert ed
for
divi
sion
t
o
1/Np;
The sign a l is applied to the
programmab le
divider and
divided
t
o
l
/N
.
T
h e result
is
c
om pared w
it h a 25kHz
frequ
e n c y re
fere n c e in the phase
derector
and
error
is outpur a
s Eo
until a rnatch
is
ob t a ined a
s
in AM
operat ion
.
During FM
recept
ion . this is
oper
a
ted
b
y
the IF leve
l
derec
ti
on
a
nd zero
cr
oss
detecti
on
ci
rc u it s
in
cl ud ed
in
the FM
I
F & A
M
systern
IC
o
f Q
I03
a
nd
by
th
e
no
isc co
m po ne nt d
ete ct io n
circ u it
o
f
Q
113
.
Wh
e
n a sta ti
o
n is tu
n ed
,
th
e
o
u tp u r o
f a
ll
ou
t
p
u ts go
t
o th
e low
level
so
Q703
goes
fr
om o
n
to
o
ff,
ca
us ing
p
in 22
of t
he
con
tro lle r
IC
t
o go to th e h
igh leve
l
(0
co
mp
let
e
3U
to sea rc
h
t
unin
g.
During AM recepti
on.
this is operared
by
the IF level derec
tion included in
th e
FM IF & AM system
JC o
f
Q
I03. When a
station is tumed
.
Q703 go es to off,
causing p
in 22
o
f th
e
co ntr oll er
JC
t
o go to th
e
hi
gh
l
evel to
co m p le te a ut
o
search tu
ni ng.
-11
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