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For 3O0Qinput is fed between pins 6 and 8
with pin 5 connected
to earth direct.
8A7.2. Types of Aerial Ultimately the choice of an aerial will depend
u p o n y o r . r i l o . a l s i g n a l s t r e n g t h . Y o u r l o c a l r a d i o d e a l e r s h o u l d
k n o w
w h a t ' s i g n a l s t r e n g t h e x i s t s i n y o u r a r e a , o r i n U K ' t h e
B B C
engineeing informition service provides details of signal strerrgth
uni aouatuga of their transmitters. Stereo reception requires a
much
b e t t e r a e r i a l s y s t e m t h a n d o e s m o n o r e c e p t l o n '
I t i s h a r d l v p o s s i b l e t o u s e t o o g o o d a n a e r i a l a n d c o m m e r c i a l l y
m a d e a e r i a l s a r e a v a i l a b l e w i t h u p t o s i x e l e m e n t s '
F o r b e s t r e s u | t s t h e a e r i a l s h o u l d b e m o U n t e d a s h i g h a s p o s s i
preferably on the roof '
A s i m p l e d i o d e c a n b e m a d e a s s h o w n i n f i g ' 8 A 7 2 1 ' w h e r e t w o
p i e c e s o f w i r e a r e c o n n e c t e d , o n e t o t h e i n n e r , o n e t o t h e o u t e r o f
i h " . o u * t o f o r m a
' T '
a e r i a l , 5 ' a c r o s s t h e t i p s o f i t s
' a r m s ' T h e w i r e
i s t a o e d o r p i n n e d t o a p i e c e o f w o o d .
BA 7.2.7
SimPle diPole aerial
F , i s f i x e d b y t h e m i d p o i n t o f t h e p a s s b a n d o f t h e c e r a m i c f i l t e r
X 1 a n d i s a p p r o x i m a t e l y 1 0 . 7 M H 2 . N o t e t h a t t h e R ' F s i g n a l m i x e s
w i t h t w i c e t h e l o c a l o s c i l l a t o r f r e q u e n c y t o p r o d u c t t h e I F R V l i s
t h e t u n i n g c o n t r o l , a n d R V 2 a n d R V 3 s e t t h e t u n i n g r a n g e a n d
t r a c k i n g : R V 2 d e t e r m i n i n g t h e L . F . a n d R V 3 t h e H F e n d ' N o t e t h a t
t h e A . F . C . a d j u s t m e n t , R V 4 , a l s o c o n t r o l s t h e . v a r i c a p s u p p l y , t h u s i t
i s n e c e s s a r y t o s e t t h e A . F ' C . b e f o r e a d j u s t i n g t h e t r a c k i n g T e m -
p e r a t u r e c o m p e n s a t i o n i s a c h i e v e d b y t h e u s e o f a t h e r m i s t o r ' T H 1 '
T h e l . F . c o i l L ' l i s t u n e d t o t h e l . F . p a s s b a n d b y o b s e r v i n g t h e
w a v e f o r m a t t h e c o l l e c t o r o f T R 2 . T R 3 a m p l i f l e s t h e l F o u t p u t f r o m
t h e m i x e r a n d p r o v i d e s m a t c h i n g t o t h e c e r a m i c f i l t e r , X l
T h e
o u t p u t f r o m X 1 i s f e d i n t o t h e b a l a n c e d c o i n c i d e n c e d e t e c t o r l C 1 ' A
a d j u s t s t h e p h a s e o f t h e s i g n a l i n t h e d e t e c t o r c i r c u i t a n d s h o u l d b e
s e i t o g i v e a s y m e t r i c a l
' S '
c u r v e w i t h a F . M s w e e p s i g n a l a p p l i e d
l c l h a i a l i m i t i n g c i r c u i t b e f o r e t h e d e t e c t o r s t a g e w h i c h p r o v i d e s a
v e r y g o o d d e g r e e o f a . m . r e j e c t i o n . T h e A ' F ' C ' v o l t a g e i s d e r i v e d
f r o m p i n 8 o f t C t v i a R 1 3 , R 1 4 , R 1 5 a n d i s u s e d t o c o n t r o l t h e v o l t a g e
a p o l i e d t o V C 1 . W i t h t h e A . F . C . s w i t c h o u t R V 4 p r o v i d e s t h e
reference voltage.
D e - e m p h a s i s o f S C p S i s f i x e d b y C 1 3 . S h o u l d 7 5 s S d e e m p l r a s i s
b e r e q u i r e d ( N o r t h A m e r i c a ) a 1 2 0 0 p F c a p a c i t o r s h o u l d b e w i r e d
a c r o s s C 1 3 . F o r s t e r e o o p e r a t i o n w i t h a n y d e c o d e r , C 1 3 m u s t b e
disconnected by cutting across the printed circuit at points marked
, X "
T h e s u p p l y r a i l i s s t a b i l i s e d a t 1 2 v o l t s b y t h e z e n e r d i o d e D 2 '
T h e d i a g r a m b e l o w s h o w s a s i m p l e r a d i o a e r i a l t h a t c a n b e m a d e
for use in a car. A piece of brass rod is soldered to the centre
C o n n e c t i o n o f a U H F p | u g a n d b e n t 4 5 o . T h e r o d m U s t b e i n s u
f r o m t h e s k i r t o i t h e p l u g , w h i c h c a n b e d o n e b y f i l l i n g t h e
p l u g b o c l y
w i t h A r a l d i t e o r s i m i l a r e p o x y a d h e s i v e .
BA4
S i z e
T u n i n g r a n g e
Aerial type
Sensitivity
A u d i o o u t P u t
O u t p u t l o a d i m P e d a n c e
Distortion
Power requtrements
Typical Performance
8 5 x 5 0 x 2 0 m m
8 7 . 5 t o 1 0 8 M H z
7 5 O o r 3 0 0 0
5 m V f o r 3 0 d b s i g n a l t o n o i s e ( m o n o )
3 0 0 m V f o r 7 5 K H z d e v i a t i o n . 1 0 0 m V f o r
307o modulation
n o t l e s s t h a n 1 0 K ! l
< 0 . 3 o / o a t l K H z a n d 7 5 K H z d e v i a t i o n
23 to 30v (max. 40mA)
B A 5
C o n n e c t i o n s t o t h e t u n e r , s h o w n n u m b e r e d i n f i g a r e :
Pin 1 + ve powPr 23-30v
2 D e c o u p l i n g ( s e e t e x t )
3 A u d i o o u t p u t
4 S i g n a l a n d P o w e r ( - v e ) e a r t h
5 Aerial centre tap
6 A e r i a l i n P u t
7 Alternative earth
8 A e r i a l i n P u t
BAO
Power suPPlY see section B.6
BA7 Aerials
BA7.1. Connections You may use either a 3000one or a 750one 75(l
i s m o r e c o m m o n i n U . K . b u t 3 0 Q O i s u s e d i n m a n y o t h e r p a r t s o f t h e
w o r l d .
O u r l a y o u t ( s e c t i o n 4 ) s h o w s a 7 5 ! ) a e r i a l .
F o r 7 5 0 : c o n n e c t s c r e e r l t o p i n 5 a n d t h e i n n e r c o r e t o p i n 6 ' N o t e
that Din 5 is connected by the aerial socket to earth'
1 4
BA 7.2.2
SintPle car aerial
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