Icom IC-FR3000 Service Manual page 79

• IN CASE OF THE AF SIGNAL FROM THE ANTENNA
CONNECTOR
The AF signals (received signals) from the antenna connec-
tor (RX unit; J1) are applied to the buffer amplifier (IC9),
CTCSS detector (IC29) and AF amplifier (IC6). The ampli-
fied signals are applied to the expander IC (IC25) to adjust
to a level needed. The adjusted signals pass through the
RPT AF mute switch (IC14), and are applied to the limiter
amplifier (IC3).
• IN CASE OF THE 2/5TONE SIGNALS
The 2/5TONE signal from the CPU (IC33, pin 43) are
applied to the mixer amplifier (IC3) via TX signal filter cir-
cuit (IC3).
• IN CASE OF THE DTMF SIGNALS
The DTMF from dialler IC (IC47, pin 14) are applied to the
mixer amplifier (IC3) via the TX signal filter circuit (IC3).
• IN CASE OF THE CTCSS AND DTCS SIGNALS
The CTCSS and DTCS signals from the CPU (IC33, pin 44)
are applied to the TX-tone filter (IC4, pins 12, 14). The fil-
tered signal are applied to the converter IC (TX unit; IC5) to
adjust tone level, and are then mixed with AF signal at the
mixer amplifier IC (TX unit; IC6).
3-2-2 MODULATION CIRCUIT (TX UNIT)
The modulation circuit modulates the VCO oscillating signal
(RF signal) using the AF signals.
The filtered signals from the LOGIC unit are applied to the
D/A converter (IC5, pin 4) to adjust AF level. The adjusted
signals are applied to the mixer amplifier IC (IC6, pin 1) with
the CTCSS/DTCS signals.
The CTCSS/DTCS signals from the CPU (LOGIC unit; IC33,
pin 44) are pass through the TX-tone filter (LOGIC unit; IC4)
and are then applied to the D/A converter (IC5 pin9) to
adjust tone level.
The mixed signals are applied to the TX VCO circuit to mod-
ulate the oscillated signal (TVCO unit; D5). The TVCO out-
put is amplified at the buffer amplifiers (Q1, Q2) and is then
applied to the drive amplifier circuit.
• APC CIRCUIT (PA UNIT)
TX UNIT
YGR
Q1
+9V
SW
TMUTE2
PRI AMP
ATT
LPF
VCC
APC
Q6,Q7
Q5
CTRL
TMUTE2
To IC33; pin 46 (LOGIC UNIT)
To IC33; pin 47 (LOGIC UNIT)
3-2-3 DRIVE AMPLIFIER CIRCUIT (PA UNIT)
The drive amplifier circuit amplifies the VCO oscillating sig-
nal to the level needed at the power amplifier.
The RF signal from the TX unit pass through the attenuater
circuit (R12–R14), the low-pass filter circuit (L1, L13, C3,
C4, ) and is then applied to the YGR amplifier (Q1). The
amplified signal passes through the low-pass filter circuit
(L4, L5, C8, C9, C56, C66), the attenuater circuit (R3–R5)
and is then applied to the pre-drive amplifier IC1.
3-2-4 POWER AMPLIFIER CIRCUIT (PA UNIT)
The power amplifier circuit amplifies the driver signal to an
output power level.
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 is passed through the low-pass filter cir-
cuit (L8–L10, C24–C26, C30–C32) and APC detector (R8,
R9, R25, R26, R29, R30, C88, C89, D2, D4), and are then
applied to the antenna connector.
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.
3-2-5 APC CIRCUIT (PA 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-
IC1
LPF PWR
ATT
Q2
PCON (TX UNIT; IC5)
AMP
IC2
FWSWR
RVSWR
3 - 3
LPF
DET