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26
3.
DATA
SERVICE
3.1.
C i rc u it desc ription
3. 1.1. HF·OSCILLATOR
( F ig. 25)
The frequency of the h.f.-oscil l ator is determi ned by the resonant ci rcu it, wh ich can be switched separatel y to
the col l ector c i rcuit of transistor 30 1 . I n conjunction with transistor 302 self-excitation occurs at the osc i l l at ion
frequency due to positive feedback. The a m p l i tude may be adjusted with potentiometer 6 1 2.
Transistors 30 1 a nd 302 are coupled via an automatical l y control l ed and reg u l ated current source 305/306.
The ampl itude of the osc i l l ator is stabi l ized via this current source. The requ i red control voltage is obtai n ed by
rectify i ng the output-ampl itude of separating-amp l i fier 303/304 by diodes 406 and 407. D i odes 404 and 405
serve for temperature compensatio n .
T h e begi n- a n d e n d frequencies of every range a r e tuned with adjusta b l e coi l s a n d capacitors; adjusti ng is
fac i l itated by using seri es and parallel capacitors. With triple tuni ng capacitor 599 , five ranges can be c a l ibrated
on two scales; the frequency response of the rema i n i ng fou r ranges is m arked on separate sca les. Both i .f. ranges
0.4 ... 0. 5 M Hz and 1 0.3 . . . 1 1 . 1 M Hz - have separate scales.
-
The sca le, corresponding with the sel ected frequency range, is ind icated by one of the six LED's 491 . . . 496.
-12V
511-613
Fig. 25. HF- Oscillator
769
527
302
" , $ ' " "
- �8 v
- 18 V
C>
6'7
303. 30"
516
-12V
DC
HF
,.0
"06 .
7
MAB2i8
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