Philips Pm 5326 Bedienungsanleitung Seite 97

t o
unit 5,
RF
OUT
,
7
generator
LF sweep
1 .
%'--
generator
(1670
Fi 9.
L.1
-
L
LF s w e e p generator : blanking circuitry
The s i n u s o i d a l wobbulating v o l t a g e of 50 H z
i s
d e r i v e d from t h e mains
t r a n s f o r m e r , f i l t e r e d by 682/527 and 621/528 and f e d t o t h e phase
s h i f t i n g s t a g e 306.
A s
i n t h i s mode of o p e r a t i o n t h e r e t r a c e
i s
n o t
blanked, t h e sweep and r e t r a c e c u r v e s can be i d e n t i c a l l y covered on
t h e o s c i l l o s c o p e by t h e LF PHASE potmeter 601/b.
The peak v a l u e of t h e t r i a n g e l
i s
s e t by 652/U6, t h e amplitude of t h e
sinewave i s a d j u s t e d t o t h a t v a l u e by 623 and 683/U6.
For X-deflection of an i n d i c a t o r b u f f e r 356 s e r v e s t o a d a p t t h e wob-
b u l a t i n g s i g n a l t o t h e MOD/SWEEP O U T o u t p u t . For
AM
t h e modulating s i g -
n a l
i s
a p p l i e d t o t h a t o u t p u t . T r a n s i s t o r 308 s e r v e s f o r b u f f e r i n g t h e
MOD I N e x t e r n a l modulating i n p u t .
4.1.3
Frequency marker part
The modulator for the frequency marker
301, 302, 303
is a transistor
coupled differential amplifier. The current via differential stage
303
is modulated by the
RF
signal ofthe VCO. The active stage
301
controls
the current in the rhythm of the RF sweep signal. By this means side
muencies are generated which are decoupled by the band pass filter
amplifier I C
3 5 7 / ~ 6
and looped via
608
and
609
to the Y-channel of
the wobbulating indicator. The bandwidth of the filter is switched over
due to the chosen sweep range. The accuracy and stability of the
travelling marker are those of the RF frequency, see fig.
3.3-14.
The fixed marker generator, multivibrator
309/310
and
10:1/10:1
divider
357
of unit
4
produce frequencies of
1
MHz
with a duty cycle of
5:1,
100 kHz
and 10 kHz. Gates
358
pass the relevant side frequencies via
305
(blanking
stage for retrace) and separating stage
304,
additionally controling
the current of the frequency marker modulator, whereby the RF frequency is
designed as carrier, which is amplitude modulated by the fixed marker
frequency and some of its side frequencies, see fig.
3.3-15,
middle.
When tuning the RF marker, the side frequencies are travelling in fixed
distance. So a travelling fixed marker spectrum origines. The distance
of the marker is adjusted by potmeter
677.
The u n i t 8 , mounted t o t h e d i s p l a y and time base c i r c u i t r i e s , u n i t s 3
and 2 , s e r v e s f o r convenient a d j u s t i n g t h e c a r r i e r frequency when
o p e r a t i n g t h e i n s t r u m e n t i n t h e sweep ranges.
A t
b e a t frequency of t h e RF g e n e r a t o r and t h e sweep o s c i l l a t o r t h e L E D
i n d i c a t o r M A R K E R a t t h e f r o n t p l a t e
i s
dimmed and f l i c k e r s , e f f e c t e d by
i n t e r l a c i n g t h e cathode p a t h of t h e i n d i c a t o r v i a I C 351.