27
3. 1 .2.
AMPLITUDE MOD UL ATOR
( F ig. 26)
The output signal of the h.f. oscillator is appl ied to the base of transistor 308 via separating ampl ifier 303/304
( Fig. 25). Moreover, via stage 307 two components of the modu l ation voltage are suppl ied to m odu lation
stage 308. The working point of modulation stage 308 is adjusted with potentiometer 63 1 so that d i fference
amplifier 308/309 is symmetrical. One component of the modu lation voltage is suppl ied to th e em itter of
modulation stage 308 via the emitter of transistor 307. The modu lation current i L F , which is determ i ned by
resistor 626, is suppl ied by tra nsistors 308 a nd 309; every transistor supp l ies half the current.
The current which passes through transistor 308 causes mod ification of the transconductance (sh ifting of the
characteristic) and thus modu l ation of the r.f. ampl itude. The modulated r.f.·signal is availab l e at resistor 634 .
The I .f. component across resistor 634 decreas i ng simu l taneously wou ld cause an i nterference signal superimposed
on the modul ated signal especially at low h.f.- and at h igh I.f
.
frequencies.
This phenomenon is compensated for by supp l ying the decreasi ng modu lation frequency in a nti-phase - ava i l able
across resistor 624 - to resistor 634 via resistor 625. Resistor 625 is dimensioned in such a way that the passing
current amou nts to i L F/2 thus compensating for the modu lation current th rough resistor 634.
i n mode wobble (WOB.) this stage is used for blanki ng the fly-back. In normal operation d iode 408 is blocked;
during wobbu lating the diode becomes conductive by a positive blanki ng pu lse, thus interrupting the h .f.-signal
during the fly-back time of the wobble action.
3 0 7
-
7
2 V
628
-
78
v
Fig.
26.
Amplitude modulator
3. 1 . 3.
FREQUENCY MODULATOR
' H F
309
6 7 9 5 3 1 6 3 2
1. 08
- 78V
""'AS219
F requency modu lation is effected by voltage-contro l l ed capacitance diodes 40 1 , 403 and 402//4 1 1 //4 1 2.
The capacitance diodes influence the oscil lating circu it of ranges 75 ... 1 1 0 M H z , 0.4 . . . 0.5 M H z and 1 0.3 . . .
1 1 .1 M H z v i a isolating capacitors 520, 522 a nd 52 1 //539.
The frequency sweep is adjusted with potentiometers 608, 607 and 609. Capacitor 566 raises the h igh cutoff
frequency in the VH F range.
Содержание PM5324
Страница 1: ...HF Generator 100kHz 110MHz PM5324 9452 053 240 1 9499 450 05511 730801 1 01 ...
Страница 15: ...14 Fig 4 Front view Fig 5 Rear view ...
Страница 43: ...Fig 33 Front view with item numbers Fig 34 Bottom view ...
Страница 44: ...44 Fig 35 Top view Fig 36 Left side view ...
Страница 45: ...45 0 0 0 0 1 ji I I MAB225 Fig 37 Scale dri ve n ...
