Philips PM 5326 Instruction Manual page 96

4.1.2 RF sweep part
The
R F
sweep g e n e r a t o r on u n i t 4 i s an e m i t t e r - c o u p l e d m u l t i v i b r a t o r
I C
352, a c t i v a t e d i n i t s 4 r a n g e s by s w i t c h i n g i n t h e c a p a c i t o r s 510
t o 514 c o v e r i n g t h e main a u d i o and v i d e o I F 's. The s i g n a l i s semi-
r e c t a n g u l a r , s e e c h a p t e r 3.3.6.2.
The l i n e a r f u n c t i o n between c o n t r o l v o l t a g e and o u t p u t f r e q u e n c y re-
s u l t s i n a l i n e a r sweep w i t h o u t a d d i t i o n a l components. The c e n t e r £ r e -
q u e n c i e s a r e a d j u s t e d by d . ~ . v o l t a g e s . The main components a r e p o i n t e d
o u t i n t h e f u n c t i o n diagram F i g . 4.1-3.
Extended s w i t c h i n g and a d j u s t m e n t s s e r v e s f o r c o n v e n i e n t o p e r a t i n g t h e
sweep mode: t o g e t h e r w i t h t h e w o b b u l a t i n g r a n g e s t h e c e n t e r f r e q u e n c y ,
t h e w i d t h and marker d i s t a n c e of t h e spectrum i s a u t o m a t i c a l l y s w i t c h e d
o v e r .
The F M o r w o b b u l a t i n g s i g n a l r e s p e c t i v e l y p a s s e s d.c. decoupled v i a 551
t o t h e summing p o i n t .
The power s u p p l y
. -
f o r t h e
R F
sweep g e n e r a t o r i s f i l t e r e d by t h e regu-
l a t i n g power c o n t r o l
I C
351 i n o r d e r t o p r e v e n t m o d u l a t i n g t h e m u l t i v i -
b r a t o r by n o i s e of t h e power s u p p l y . P o t m e t e r 604 a d j u s t s t h e s u p p l y
v o l t a g e .
1
FM
Fig.
L . l - 3
RF sweep; control of multivibrator MC 1 6 5 8 P
The L F sweep generator I C 355/u6, F i g * 4-1-4,
produces time-symmetrical
trangular and square wave signals, the frequency of which is set by
capacitor
533
and overmore can be varied between
3
and 30
Hz
by potmeter
601/a L F FREQUENCY. During the second half period transistor
307
cutts
off the
RF
path via diode 406 and transistor 308 and prevent the markers
of the fixed marker generator getting to the marker modulator 301, 302
of unit
4 .