Yaesu FT-902DM, Instruction Manual

Page: 37 / 55

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J
M EM O R Y
U NIT
( P B- 1 7 8 7 0 )
The
V FO s i gn a l d e l i v e re d t o p i n
4
o f
PB- 1 7 8 70
i s
a m p l i fi e d b y 0 2 8 0 9 ( 3 S K40M ) a n d 0
2 8
1
0
( 2 SC
7 8 5 ) ,
a n d
fe d
t o
c
ou n
t
e
r ga te 0 2 8 1 3
(
S N 7 4
LSOON
). A
c l oc k s i g n a l
g
e n
e
r
a
t
or 0 2 8 1
1
(
M S
M
5 5 6 2 )
p
ro d
u
c e s
5 0 H z
c
l o c
k
pu lses from a c ry s t a l
fre q u e n c y o f
3 2 7 6 . 8
k H z . Th e p u l se s
w h i c h
passed
t h rough t h e
ga
t e a re
fe d
t o
a
si x d i gi t d ecad e
c o u n te r Q 2 8 1 5
(TC503 2P) , w h i c h
c o u n t s t h e
V FO
fre q u e n c y . Th e
BCD
o u tpu t fro m
02 8 1 s
i s
fe d
t
h r o u
g
h 0 2 8 2 2 - 0 2 8 2 6
(
a l
l
M C l 404 2 B) t o
u p / d o w n
c ou n t
e
r 0 2 8 2 7 - 0 2 8 3 1 ( SN 7 4 LS 1 92N ) .
w h i c h p re se ts t h e V FO fre q u e n c y .
The
5
.
0
- 5 . 5
M H z
s i
g
n a l ge nerated b y 02 8 0 1
( J F I 03 3 8 ) i s fe d
t h rou gh
b
u
ff
er
/
a m p l i
fi
e r 0 2 8 0 2
( J F l 03 3 ) a n d Q 2 8 0 3
(
2 S
C7
8
5
) t o pulse sh a p e r
0 2 8 0 4
( 2SC78 5 ) .
LOI z'"H
0 2 0
JJ PA 54 H
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c - I
I
L S I
COUNTER
U N I T P B - 2 0 8 6 A
( NO
30• . I
_J L
- -
�
- - - - - - - - - - - - - - - - - - - - - - - - - - -
-35-
Th e
s w i t c h i n g
p u l se ge n erated by Q 2 8 0 4 is a l s o
fed
t o
0 2 8 2 7 ,
where t h e
signal is
d i v i d e d t o
1 / 5 000 t o 1 / 5 5 000 i n accordance w i t h t h e pro­
gra m p re s e t by 0 2 8 2 7 - 0 2 8 3 1 . Th e ou t p u t from
0 2 8 3 1 ( a p p rox i m a tely
1 00
Hz )
i s fe d t h rough a
on e- s h o t m u l t ivi bra t o r Q2 8 3 2 ( SN 7 4 LS I 23 N ) t o
t h e
p h a se n)m p arator 0 2 8 2 1 ( M C404 4 P ) w h e re
t h e p h ;ise o f t h e
1 00
Hz
signal is c o m p a red
w i t h
t h e
p
h
a s e o f t h e
I
0 0
H z
sign al
wh
ic h i s d e l i v e re d
from 0 2 s 1 1
·
The
DC
o u
t
p u
t
from Q 2 8 2 1 passes
t
hr
o
u g
h
a l o
w
p ;i ss f i l t e r
,
o p e r a
ti
o n a l a m p l i f
i
e r Q 2 8 2 0 ( LM 308 ) ,
t o re m ov e t h e
I
0 0
Hz
r i p p l e
.
Th i s
D C
v o l t ;i g e
i s
a p p l i e d t o v;irn c t or
d i o d e s
D 2 8 0 6 - D 2 8 0 7
( M V -
1 04 ) .
thus l o
c
k i n
g
t h e
VCO freq u e n c y .
W h e n t h e
M
( m e m o ry )
swi tch
i s p u s h e d
,
the
c o u n t e r o u t pu t from
0 2 8 1 5 is
l
a
t
c
h e d a n d
t
h
e
VCO fre q u e n c y i s
l ocked .