Kenwood TK-190 Service Manual page 15

4-5. APC circuit
The APC circuit always monitors the current flowing
through the RF power amplifier (Q1, Q2) and keeps a con-
stant current. The voltage drop at R14, R15, and R16 is
caused by the current flowing through the RF power ampli-
fier and this voltage is applied to the differential amplifier
(IC2 1/2).
IC2 (2/2) compares the output voltage of IC2 (1/2) with
the reference voltage from IC1, and the output of IC2 (2/2)
controls the VGC of the RF power amplifier to make the both
voltages to same voltage.
The change of power high/low is carried out by the
change of the reference voltage. Q4, Q5, and Q8 are turned
on in transmit and the APC circuit is active. (See Figure 6)
5. PLL Frequency Synthesizer
The frequency synthesizer consists of the VCXO (X1),
VCO (L800), PLL IC (IC101) and buffer amplifiers.
The VCXO generates a 16.8MHz reference frequency.
The frequency stability is within ± 5.0ppm (temperature
range of –30 to +60°C).
The output of the VCXO is applied to pin 8 of the PLL IC.
The VCO of TK-190 covers a 7.3MHz frequency spread.
VCO (L800) has 2 internal VCOs. One for the 1st local
oscillator (158.25 – 166.005MHz) and another one for the
2nd local oscillator (129.05MHz). Each output is connected
to a dual PLL IC (IC101).
VCO1 oscillates at 158.705 – 166.005MHz during trans-
mission and it oscillates at 158.205 – 166.55MHz during re-
ception.
VCO2 oscillates at 129.005MHz during both reception
and transmisson. However, the oscillated signal is modu-
lated during transmission.
Each PLL circuit has LPFs and buffer amplifiers.
The output of VCO1 goes through the buffer amplifier,
then the output is switched either for the 1st local oscillator
circuit of the receiver or transmitter.
The output of VCO2 goes through the buffer amplifier.
The output is connected to both the receiver and transmitter
2nd local oscillator circuits.
CIRCUIT DESCRIPTION
6. Power Supply Circuit
minal connected to the TX-RX unit. After passing through
the power switch power supply (SB) is applied to the two
AVR ICs, and AVR circuit.
supplies 5V (5C) to the common circuit. AVR circuit
(Q400,Q402) supplies voltage to the TX circuit. 5R and 5RB
is 5V for reception and output during reception. 5T and 5TB
is 5V for transmission and output during transmission.
Battery
VCO1 BUFF
LPF BUFF
16.8MHz
TCXO
Dual PLL
UL
DT,CLK,LE
CPU
LPF BUFF
MOD/TONE
VCO2 BUFF
Fig. 7 PLL block diagram
Battery +B is supplied via a 3A fuse from the battery ter-
IC401 supplies 5V (5CM) to the control circuit. IC402
Fuse
3A
SW
5V REG
Power
PSW
SW
5V REG
5CC
from CPU
from CPU
Fig. 8 Power supply circuit
TK-190
TX
SW
LOCAL1
5TB/5RB
RX
LOCAL1
TX
LOCAL2
RX
LOCAL2
+B
SB
5CM
5C
5RB
SW
5R
SW
5TB
SW
5T
SW
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