Philips D2935 - Radio Circuit Architecture; General Block Diagram; Wideband Pre-amplifier Circuit; Aerial Switching Mechanism

CIRCUIT DESCRIPTION
BLOCK DIAGRAMS
GENERAL BLOCKDIAGRAM
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7
)
98,2~ 118. 7MHz
AM- CIRCUIT
WIDESAND PRE- AMP.
(148- SUISTKR)
Fig. 8 PRS 00178
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I
I
I
|
|
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! 0.146 7 30 — MHz
3
!
|
:
| Wide-band pre-amplifier (see Circuit Diagram 1)
!
ade nekeie eae ereemeee anes eeeeeeaseee ee Baie ne ag There are 2 built-in antennas:
Fig. 4 LW-MW > (< 1622 kHz) ferroceptor 1012 (via
FET6121)
SW > (> 1622 kHz) telescopic aerial (via
FET6120)
are automatically changed over by output D
AF QUT (< 1622 kHz) of pP.
DETECTOR
LW and MW: D= high (+5 volts).
6125 is conducting.
Gate 6120 is low via diode 6172.
6126 cuts off.
Gate 6126 high, so that the ferroceptor
is switched on.
SW : D= low
Telescopic antenna is connected via
--— f-o03. to synth. - FET61 20.
8100
TKLOSI
Aerial switch
In the LW-MW tuning range, the user may switch offthe
ferroceptor and use the telescopic aerial which has
Fig. 5 better sensitivity.
(lf a strong transmitter signal occurs in the LW-MW
frequency range, there is a chance of the set becoming
overloaded). 3
PRS.00130
TRADSZ0
ig ile Frequency range
‘ ye The frequency range is controlled with output D
(<< 1622 Kc) of uP.
LW-MW : 6129 is conducting
Feedback via 2195/3208
Frequency range see Fig. 7.
¥ TUNE
220)
Spanien SW : 6129 cuts off
Gate 6128 is high
TUNED OSCILLATOR OSC. 54532kHz PRE.OOL32 Feedback via 2195/3209
Pia ask Fig. 6 Frequency range see Fig. 8.
5115/2175 : 468 kHz tuned-circuit filter.
This filter has been applied to avoid
instability when the set is tuned to a
frequency round 468 kHz.
Input signal on telescopic antenna via 15 pF.
Max. input signal 50 mV.
Gain factor : (output measured after low-pass filter
2169, 5111, 2170, 5112).
AM oscillator (VCO) (Circuit round FET6132)
Frequency range : 55146-84999 kHz
In 2 steps : 55146-66649 kHz
and : 66650-85000 kHz
Change over by means of output F (<< 11.65 Mc) of yu.
0.146 | 30 At the lowest frequency step, capacitor 2204 is switcteed
Fig.
7
in
parallel
with
coil
5122.
CS 987 65
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