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3. CIRC UI T D E S CR IPTIO N
3 . 1 T U N E R S E C T I O N
S t e r e o
B P F
F M R F A
C e r o m i c
F M M i x e r
F M I F T F i t t e r
L o c o l 0 S C
C e r q m i c
A M
A M M i x e r
A M I F T
F i L t e r
l F A m p
M E T E R S I G N A L +
S w i t c h i n q
F i g . 1 6
o T u n i n g I n d i c a t o r C i r c u i t
D u r i n g F M o p e r a t i o n s , t u n i n g a s t a t i o n c a u s e s a r i s e i n
t h e v o l t a g e p r e s e n t a t t h e p i n 1 0 o f l C 1 ( K 8 4 4 1 9 C ) . S i n c e
t h i s t u r n s 0 8 O N a n d 0 1 1 O F F , c u r r e n t b e g i n s t o f l o w
f r o m R 6 5 t o D 8 , l i g h t i n g t h e t u n i n g i n d i c a t o r .
N e x t , m o v i n g t h e t u n i n g d i a l p o i n t e r t o a p o i n t n e a r t h e
s t a t i o n , b u t l o w e r o n t h e f r e q u e n c y s c a l e w i l l c a u s e o n e o f
the comparators of lC3 to gate, dropping the potential at
t h e b a s e o f Q 8 a n d t u r n i n g i t O F F . T h i s c a u s e s Q 1 1 t o t u r n
O n a n d t h e t u n i n g i n d i c a t o r w i l l n o t l i g h t . l f t h e p o i n t e r i s
m o v e d n e a r t h e t u n e d p o i n t , b u t h i g h e r o n t h e f r e q u e n c y
scale, the opposite comparator (lC3) will gate, preventing
t h e t u n i n g i n d i c a t o r f o r m l i g h t i n g a s e x p l a i n e d a b o v e .
A d d i t i o n a l l y , i n a f r e q u e n c y a r e a w h e r e n o s t a t i o n s e x i s t ,
o r w h e r e t h e i n c o m i n g s i g n a l i s s o w e a k t h a t t h e S / N r a t i o
i s u n a c c e p t a b l e , 0 8 w i l l b e O F F a n d 0 1 l w i l l b e O N . a n d
t h e t u n i n g i n d i c a t o r w i l l r e m a i n e x t i n g u i s h e d .
T h e a b o v e o p e r a t i o n s a p p l y w h e n F M m u t i n g i s a c t i -
v a t e d , a n d t h e y a r e s y n c h r o n i z e d w i t h m u t i n g o p e r a t i o n s .
D u r i n g A M o p e r a t i o n s . + B i s a p p l i e d t o l C 3 a n d i n d i c a t o r
o p e r a t i o n s a r e i n a c c o r d a n c e w i t h t h e v o l t a g e a t p i n 1 0 o f
K 8 4 4 1 9 C .
F M l F A m p
M P X
0 e c o d e r
C e r o m i c
F i l t e r
F M D e t e c t o r
t
I n d
L C n
R c h
F M o u t
A u t o / l . 4 o n o
S w i t c h
A M F E R
A n t e n n o
L o c a L 0 S C
o Front End
T h e a n t e n n a i n p u t s e c t i o n c o n s i s t s o f a b a n d - p a s s f i l t e r e d
s i n g l e s t a g e R F a m p l i f i e r ( O l ) , a b a s e i n j e c t i o n m i x e r ( 0 2 ) ,
a n d a m o d i f i e d C o l p i t t s l o c a l o s c i l l a t o r c i r c u i t .
o lF Amp, Detector Circuit
T h i s s e c t i o n i s c o n t a i n e d i n t h e F M ( A t t l t ) t F S y s t e m l C
( L A l 1 4 0 ) a n d c o n s i s t s o f t h e F M l F a m p , t w o d o u b l e -
e l e m e n t c e r a m i c f i l t e r s , t h e p r e a m p c o n s i s t i n g o f t r a n s i s t o r
03. Together they form a four-stage differential amplifier.
K B 4 4 1 9 C f u n c t i o n s a s a n l F a m p l i f i e r , l i m i t e r , a n d a s a
quandrature detector.
o F M M u t i n g C i r c u i t
O u t p u t l e v e l i s d e t e c t e d a t t h e m e t e r o u t p u t p i n ( p i n 1 0 )
o f K B 4 4 ' l 9 C b y A N 6 9 1 3 ( l C 3 ) . W h e n a d e t u n e d s t a t u s i s
detected, the signal is passed through AND gates and used
t o a c t i v a t e t h e m u t i n g t r a n s i s t o r ( O 1 0 ) .
o F M M u l t i p l e x C i r c u i t
T h e F M m u l t i p l e x c i r c u i t u s e s a P L L m u l t i p l e x l C
(KP'44248\.
r c a - r L E D D r i v e r
A M I F T A M
D e t e c t o r
F u n c t i o n
S w i t c h
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