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TK-250
CIRCUIT DESCRIPTION
4. TRANSMITTER SYSTEM
4.1 Microphone
amplifier
The signal from the microphone
is high-pass filtered by
IC207
(1/2),
passed through microphone mute circuit (0202),
limited and pre-emphasized
by IC207
(2/2),
before being
passed to the low-pass filter network (IC216).
4.2 Modulator
The output of the low-pass filter network (IC216) is passed
to the DIA converter
(IC206) for maximum deviation adjust-
ment and the summing amplifier (IC201
2/2)
before being
applied to a varactor diode (0504) in the voltage controlled
oscillator (VCO) located in the frequency synthesizer section.
I
~
I
LPFI
IC207
(2/2)
IC216
C257
R263
R268
(1/2)
R252
3
+
1
.....•
6
0
8
'"
Q202
I-
M
'"
li
1!
'"
Cl:
'"
'"
0
I
1
I
H
Cl:
ü
'"
C266
I-
11
.•.....
IC216
!LPF!
T~
(2/2)
5
R279
R~",
«
I
-~I',,"I
I
A
-
6
I
BI
I
II
I
I
~
I
C276
(ADJ)
ILPFI
V02
~L.S.D
0501
0504
Fig. 4 Microphone amplifier, modulator
18
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