Icom IC-FR4000 Service Manual page 11

3-2-4 POWER AMPLIFIER CIRCUIT
(50PA OR 25PA UNIT)
The power amplifier circuit amplifies the driver signal to an
output power level.
• IC-FR4000 (50PA UNIT)
The RF signal from the pre-drive amplifier (IC1) is applied to
the power amplifier (Q2) to obtain 50 W of RF power.
The amplified signal from the power amplifier (Q2) is passed
through the low-pass filter circuit (L8–L10, C24–C26, C27,
C29–C32) and APC detector (D2, D4, R8, R9, R25, R26,
R29, R30, C88, C89), and are then applied to the TX anten-
na connector (CHASSIS unit; J1).
Control voltage for the pre-drive amplifier (IC1, pin 2) comes
from the APC amplifier (IC6, IC7, D10) to obtain stable out-
put power. The transmit mute switch (Q3, Q5, Q8, Q9, D11)
controls YGR amplifier and pre-drive amplifier when transmit
mute is necessary.
• IC-FR4100 (25PA UNIT)
The amplified signal from the power amplifier (IC2) is
passed through the low-pass filter circuit (L6, L7, L20, L21,
C1–C3, C98, C99, C117) and APC detector (D2, D4, R7,
R8, R20, R21, R25, R26, R73, C78, C79), and is then
applied to the TX antenna connector (CHASSIS unit; J1).
Control voltage for the pre-drive (Q4) and power amplifier
(IC2) comes from the APC amplifier (IC1, Q9, Q10) to obtain
stable output power. The transmit mute switch (Q7, Q8) con-
trols the pre-drive (Q4) and power amplifier (IC2) when
transmit mute is necessary.
• POWER AMPLIFER AND APC CIRCUIT (50PA UNIT)
TX UNIT
YGR
Q1
+9V
Q5
SW
TMUTE2
• POWER AMPLIFER AND APC CIRCUIT (25PA UNIT)
DRIVE
TX UNIT
AMP
Q4
+9V
SW
Q7, Q8
TMUTE2
PRE AMP
LPF ATT
VCC
APC
Q6,Q7
CTRL
To IC33; pin 46 (LOGIC UNIT)
To IC33; pin 47 (LOGIC UNIT)
POWER AMP
LPF ATT
VCC
APC
CTRL
Q11, Q12
To IC33; pin 46 (LOGIC UNIT)
To IC33; pin 47 (LOGIC UNIT)
3-2-5 APC CIRCUIT (50PA OR 25PA UNIT)
• IC-FR4000 (50PA UNIT)
The APC circuit protects the power amplifier from a mis-
matched output load and stabilizes the output power.
The APC detector circuit detects forward signals and reflec-
tion signals at D2 and D4 respectively. The combined volt-
age become minimum level when the antenna impedance is
matched at 50 Ω, and the voltage is increased when it is
mismatched.
The detected voltage is applied to the APC amplifier (IC2,
pin 3), and the power setting "PCON" signal from the D/A
converter (TX unit; IC5), controlled by the CPU (LOGIC unit;
IC33), is applied to APC amplifier (IC2, pin 1) for reference.
When antenna impedance is mismatched, the detected volt-
age exceeds the power setting voltage. Then the output volt-
age of the APC amplifier (IC2, pin 4) controls the input cur-
rent of the drive amplifier (IC1, pin 2) to reduce the output
power.
• IC-FR4100 (25PA UNIT)
The APC detector circuit detects forward signals and reflec-
tion signals at D2 and D4 respectively. The combined volt-
age become minimum level when the antenna impedance is
matched at 50 Ω, and the voltage is increased when it is
mismatched.
The detected voltage is applied to the APC amplifier (IC1 pin
3), and the power setting "PCON" signal from the D/A con-
verter (TX unit; IC5), controlled by the CPU (LOGIC unit;
IC33), is applied to the the APC amplifier (IC1 pin 1) for ref-
erence. When antenna impedance is mismatched, the
detected voltage exceeds the power setting voltage. Then
the output voltage of the APC amplifier IC (IC1, pin 4) con-
trols the input current of the power amplifier IC (IC2, pin 2)
to reduce the output power.
IC1
PWR
LPF ATT
Q2
PCON (TX UNIT; IC5)
AMP
IC2
FWSWR
RVSWR
IC2
LPF
DET
PCON
(TX UNIT; IC5)
AMP
IC1
FWSWR
RVSWR
3 - 4
LPF
DET