TKR-750
13
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.
TEMP
Final unit (X45-373 A/2)
PC
POWER ADJ
Vcont
TX ANT
ATT
TCXO
FCT
X3
16.8MHz
BUFF
IC1
MB
MO
TX-RX unit (X57-695 A/2)
CM COUPLER
REF
AMP
DC
AMP
VR1
SW
STT
Q11
Q2
Drive AMP
Q4
Drive AMP
Q5
Final AMP
IC1
IC1
Q8
D4
D5
Q3
Drive AMP
TX VCO
A2
(X58-479)
FWD
DET
REV
DET
PDT
(to IC604 CPU)
Fig. 3
Driver and final power amplifier circuit
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.
FAG
FAB
CN4
Q9
TMP
FAS
IC2
13
Q6
IC7
CK,
DT,
STB
CPU
IC604
TMP
17
Q602
+B
X45 A/2
X57 A/2
X57 B/2
FAN
OFF
ON
+20
°
C
+30
°
C +35
°
C +40
°
C
+50
°
C
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.
[Fan operation]
Fig. 4
Fan action control circuit
CIRCUIT DESCRIPTION