Kenwood TKR-850 Service Manual page 20

TKR-850
3-3. Driver and Final Power Amplifier Circuit
The transmit signal is generated by the TX VCO (A2),
amplified by Q11, and sent to final unit (X45-363). This am-
plified signal is amplified by Q1, Q2, Q3, and Q4, and is
passed to the FINAL stage. The RF power amplifier consists
of MOS FET.
TX-RX unit (X57-627 A/2)
STT
MO
TX VCO
A2
(X58-481)
FCT
BUFF
MB
IC1
16.8MHz
3-4. Automatic Power Control, Circuit and Transmitter
The automatic power control (APC) circuit stabilizes the
transmitter output power at a pre-determined level, and con-
sists of forward/reflected power detector circuits, and
switching transistor Q8. The forward/reflected power de-
tector circuits detects forward RF power and reflected RF
power to DC voltage, and consists of a CM coupling type
detection circuit formed by a strip line, RF detector D4/D5,
and DC amplifier IC3 (A/2).
The voltage comparator (IC3 B/2) compares the above
detected voltage with a reference voltage, set using the mi-
croprocessor and IC6 located in the TX-RX unit. An APC
voltage proportional to the difference between the sensed
voltage and the reference voltage appears at the output of
IC3. This output voltage controls the gate voltage for the
drive amplifier Q4 and final amplifier Q5, which keeps the
transmitter output power constant.
3-5. Fan Action Control Circuit
If fan action is set to "Temperature", the cooling fan is
turned ON or OFF according to temperature.
If the ambient temperature of the final unit exceeds
approx. 40°C, the output from pin 6 of the temperature de-
tection IC1 changes from L to H. This signal is sent to the
CPU (IC604) by Q602 in the TX-RX unit B/2 (control section),
and the output from pin 13 (FAS) of IC7 in the TX-RX unit A/
2 controlled by the CPU goes H.
This signal turns Q9 in the final unit ON to run the cooling
fan. It has a hysteresis of approx. 5°C by IC2. If fan action is
set to "Continuous", the fan operates continuously, but Q9
stays ON.
20
CIRCUIT DESCRIPTION
Final unit (X45-363 A/2)
Q11
ATT
TCXO
X3
Fig. 3 Driver and final power amplifier circuit
Q1 Q3 Q4
Drive AMP Drive AMP Drive AMP
Q2
Vcont
Drive AMP
IC3
DC
AMP
REF
PC
AMP
IC3
FAN
CN4
FAB
FAG
[Fan operation]
OFF
+20°C
Fig. 4 Fan action control circuit
Q5
Final AMP
CM COUPLER
TEMP
D4 D5
REF FWD
DET DET
Q8
SW
POWER ADJ
VR1
X45 A/2 X57 A/2
IC7
+B
BU4094BCF
Q9
FAS
13
Q6
IC1
TK11050M
VTH
6
OUT
+30°C +40°C
TX ANT
X57 B/2
IC604
CPU
CK,
TEMP
DT,
17
STB
Q602
ON
+50°C