Kenwood TK-190 Service Manual page 14

TK-190
4. Transmitter System
4-1. Microphone amplifier
The signal from IC3 (control unit) goes through the mute
switch (Q403).
When the SP-MIC is not attached, the microphone
switching terminal (MSW) on the universal connector be-
comes High, and mute switch (Q403) is turn on. When the
SP-MIC is attached, MSW is connected to GND at inside of
SP-MIC. For this reason, Q403 is turned off, the internal
microphone is muted, and only the input of the external mi-
crophone is supplied to the microphone amplifier of the TX-
RX unit.
The signal from microphone passes through the limiter
circuit in D601, through the high-pass filter, the ALC circuit,
the low-pass filter, the high-pass filter, and pre-emphasis/
IDC circuit in IC607. When encoding DTMF, mute switch
(Q601) is turned off for muting the microphone input signal.
The signal passes through the D/A converter (IC603) for
the maximum deviation adjustment. And enters the sum-
ming amplifier consisting of IC605 (1/2), and is mixed with
the low speed data from the CPU (IC406).
The output signal from the summing amplifier goes to
the VCO2 modulation input.
4-2. Noise cancelling microphone circuit
The two signals from INT MIC (Main & Sub) are input to
the positive (+) input (Sub) and to the negative (–) input
(Main) of the IC3. If the same signal is input to both Main
and Sub, the Main signal is canceled at the output of IC3 (pin
7). In other words, noise words, noise from nearby sources
not directly connected the transceiver enters the Main and
Sub inputs at the same signal and is therefore canceled out.
When a signal is only input to Main and there is no signal
at Sub, the Main signal is output as is, from IC3 (pin 7). In
other words, only the voice audio of the operator in ex-
tremely close proximity to the Main MIC is input to Main so
that the signal is output as is from IC3 (pin 7). Also, when
the "N/C" switch is set to "L", transistor Q14 turns off so Sub
microphone turns off and operation is the same as above.
EXT.
MIC
IC3
Q403
MAIN
N/C
MIC SW
AMP
MIC
SUB
(CONT)
MSW
14
CIRCUIT DESCRIPTION
IC607 2 15
D601
12
LIMIT HPF ALC
IC603 IC605 (1/2)
Q404
D/A
SUM
AMP
I4 O4
LSD
Fig. 5 Microphoen circuit
4-3. Down-mixer
At Q102, a modulated VCO2 signal is mixed with 2nd lo-
cal oscillator signal, 129.005MHz. The difference of the two
signals is used for the transmission signal (29.7 – 37MHz).
The output was filtered through a LPF (Low Pass Filter).
4-4. Drive and Final amplifier
The signal from Down-mixer is amplified by the pre drive
(Q32) and drive amplifier (Q1) to 500mW. The output of the
drive amplifier is amplified by the RF power amplifier (Q1,Q2
in the FINAL unit) to 6W (1W when the power is low).
The RF power amplifier consists of two MOS FET transis-
tor. The output the RF power amplifier is then passed
through the transmit-receive (TX-RX) antenna switching (D2
is on) and the harmonic filter (LPF) and applied to the an-
tenna terminal.
From
T/R SW
(D7)
REF
VOL
(IC1)
Fig. 6 Drive and final amplifier and APC circuits
MM
TONE
Q601
SW
16 18 19
HPF
PRE
COMP LPF HPF IDC
EMP
L800
VCO
Q1,Q2
Q32 Q1 FINAL unit
Pre- RF
DRIVE
DRIVE
POWER
AMP
AMP AMP
R14
VDD VGC
R15
R16
IC2
Q5
(1/2)
SW
6
D2
TX-RX
LPF
ANT
SW
Q8
SW
Q4
SW
IC2
(2/2)