Kenwood TK-3160 Service Manual page 9

D4,7
LPF
LPF
D3,9
PLL IC IC1
1/N
PLL DATA
REF OSC
1/M
X1
16.8MHz
Fig. 6 PLL circuit
3) Unlock Detector
If a pulse signal appears at the LD pin of IC1, an unlock
condition occurs, and the DC voltage obtained from C19,
R6, and Q1 causes the voltage applied to the microprocessor
to go high. When the microprocessor detects this condition,
the transmitter is disabled, ignoring the push-to-talk switch
input signal.(See Fig. 7)
IC1
R16
LD
C19
PLL IC
Fig. 7 Unlock detector circuit
4. Transmitter System
1) Microphone Amplifier
The signal from the microphone passes through IC601.
When encoding DTMF, it is turned OFF for muting the
microphone input signal by IC601.
The signal passes through the Audio processor (IC601) for
the maximum deviation adjustment, and goes to the VCXO
modulation input.
CIRCUIT DESCRIPTION
Q6
Q7
TX VCO
RF AMP
Q11
Q9
RF AMP
BUFF AMP
Q5
RX VCO
Q8, 12
T/R SW
RX
TX
5kHz/6.25kHz
PHASE CHARGE
COMPARATOR PUMP
5kHz/6.25kHz
5C
IC805
R6
R7
Q1
UL
CPU
IC601
AGC
MIC
AQUA
LPF
IC805
DTMF/2 TONE
CPU
Fig. 8 Microphone amplifier
2) Drive and Final Amplifier
The signal from the T/R switch (D201 is on) is amplified by
the pre-drive (Q206) and drive amplifier (Q207) to 50mW.
The output of the drive amplifier is amplified by the RF power
amplifier (Q211) to 4.0W (1W when the power is low). The
RF power amplifier consists of two MOS FET stages. The
output of the RF power amplifier is then passed through
the harmonic filter (LPF) and antenna switch (D204 and
D206) and applied to the antenna terminal.
Q205 Q206
From
RF Pre-DRIVE
T/R SW
AMP
AMP
(D201)
VG
+B
R256
R257
R261
PCTV
(IC805)
Fig. 9 Drive and final amplifier and APC circuit
3) APC Circuit
The APC circuit always monitors the current flowing through
the RF power amplifier (Q211) and keeps a constant current.
The voltage drop at R256, R257 and R261 is caused by the
current flowing through the RF power amplifier and this
voltage is applied to the differential amplifier IC201(1/2).
IC201(2/2) compares the output voltage of IC201(1/2) with
the reference voltage from IC805. The output of IC201(2/2)
controls the VG of the RF power amplifier, Drive amplifier
and Pre-Drive amplifier to make both voltages the same.
The change of power high/low is carried out by the change
of the reference voltage.
4) Encode Signalling
(1) QT/DQT
QT,DQT data of the LSDTCXO Line is output from pin 22 of
the CPU. The signal passes through a low-pass CR filter
and goes to the TCXO(X1).
The QT,DQT data of the LSDVCO Line is output from pin
TK-3160
VCO
LSDVCO LPF
X1
LSDTCXO LPF TCXO
D204
Q207 Q211 D206
DRIVE RF
ANT
POWER AMP
AMP SW
VG VG
VDD
IC201 IC201
(1/2) (2/2)
ANT
LPF
9