Driver And Final Power Amplifier Circuit; Automatic Power Control Circuit And Transmitter; Rf Power Down Detect; Fan Action Control Circuit - Kenwood TKR-750 Service Manual

3-3. Driver and Final Power Amplifier Circuit

The transmit signal is generated by the TX VCO (A2), am-
plified by Q11, and sent to final unit (X45-373). This amplified
signal is amplified by Q2, Q3, and Q4, and is passed to the
FINAL stage. The RF power amplifier consists of MOS FET.
TX-RX unit (X57-695 A/2)
STT
MO
TX VCO
A2
(X58-479)
FCT
BUFF TCXO
MB
IC1
X3
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/reverse power detector circuits, and switch-
ing transistor Q8. The forward/reverse power detector cir-
cuits detects forward RF power and reverse 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
IC1 (A/2).
The voltage comparator (IC1 B/2) compares the above de-
tected voltage with a reference voltage, set using the micro-
processor 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 IC1. This
output voltage controls the gate voltage for the drive ampli-
fier Q4 and final amplifier Q5, which keeps the transmitter
output power constant.

3-5. RF Power Down Detect

When the transmitter output power has dropped to or be-
low the preset values (High Power : about 20W, Low Power :
about 10W) in "RF Power Down Detect" adjustment, IC604
(CPU : X57-695) detects the drop in power and outputs a
Low-level (default) signal to the AUX out port.

3-6. 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. 35°C, the output from the temperature detection IC2
changes from H to L. This signal is sent to the CPU (IC604)
by Q602 in the TX-RX unit B/2 (control section), and the out-
put from pin 13 (FAS) of IC7 in the TX-RX unit A/2 controlled
by the CPU goes H.
CIRCUIT DESCRIPTION
Final unit (X45-373 A/2)
Q2
Drive AMP
Q11
ATT
Q3
Drive AMP
Fig. 3 Driver and final power amplifier circuit
Q4 Q5
Drive AMP Final AMP
CM COUPLER
TEMP
Vcont
D4
FWD
DET
IC1
DC
SW Q8
AMP
POWER ADJ
REF
PC
AMP
IC1 VR1
This signal turns Q9 in the final unit ON to run the cooling
fan. It has a hysteresis of approx. 2°C by IC2. If fan action is
set to "Continuous", the fan operates continuously, but Q9
stays ON.
X45 A/2
FAN
CN4
FAB
+B
Q9
FAG
IC2
[Fan operation]
OFF
+20°C +30°C +35°C +40°C
Fig. 4 Fan action control circuit
TKR-750
TX ANT
D5
REV
DET
PDT
(to IC604 CPU)
X57 A/2 X57 B/2
IC7 IC604
FAS
13
CPU
Q6
CK,
TMP
DT,
17
STB
TMP
Q602
ON
+50°C
13