Kenwood TK-2160 Service Manual page 9

D3, 5, 7, 8
LPF
LPF
D4, 6, 9, 10
PLL IC IC1
1N
PLL DATA
REF OSC
1M
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 sw itch
input signal. (See Fig. 7)
IC1
R16
LD
C19
PLL IC
Fig. 7 Unlock detector circuit
4. Transmitter System
1) M icrophone Amplifier
The signal from the microphone passes through the IC601.
When encoding DTM F, 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
DOUBLER
Q9 Q11
BUFF AMP RF 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
M IC
AQUA
LPF
IC805
DTM F/2 TONE
CPU
Fig. 8 M icrophone amplifier
2) Drive and Final Amplifier
The signal from the T/R sw itch (D201 is on) is amplified by
the drive amplifier (Q207) to 50mW.
The output of the drive amplifier is amplified by the RF pow er
amplifier (Q211) to 5.0W (1W w hen the pow er is low ). The
RF pow er amplifier consists of tw o M OS FET stages. The
output of the RF pow er amplifier is then passed through
the harmonic filter (LPF) and antenna sw itch (D204 and
D206) and applied to the antenna terminal.
Q206 Q207
From
Pre-DRIVE
DRIVE
T/R SW
AM P
AM P
(D201)
VG VG
+B
R264
R265
R270
IC201
(1/2)
PCTV
(IC805)
Fig. 9 Drive and final amplifier and APC circuit
3) APC Circuit
The APC circuit alw ays monitors the current flow ing through
the RF pow er amplifier (Q211) and keeps a constant current.
The voltage drop at R264, R265 and R270 is caused by the
current flow ing through the RF pow er amplifier and this
voltage is applied to the differential amplifier IC201(1/2).
IC201(2/2) compares the output voltage of IC201(1/2) w ith
the reference voltage from IC805. The output of IC201(2/2)
controls the VG of the RF pow er amplifier, drive amplifier
and pre-drive amplifier to make both voltages the same.
The change of pow er 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-2160
VCO
IC606
BUFFER
LSDVCO LPF
X1
LSDTCXO LPF
TCXO
ANT
D204
Q211 D206
RF
ANT
LPF
POWER AM P
SW
VG
VDD
IC201
(2/2)
9