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4-2-3 TRANSMIT AMPLIFIERS (PA-C UNIT)
The transmit signal from the VCO is amplifi ed to the transmit
output level by the transmit amplifi ers.
The transmit signal from the TX/RX switch (D16=ON,
D17=OFF) is amplified by two pre-drive amplifiers (Q703,
Q704), drive amplifi er (Q702) and power amplifi er (Q701) in
sequence to obtain 0.5 W (aprrox.) of transmit output power.
The power-amplified transmit signal is passed through the
antenna switch (D701) and LPF (as a harmonic fi lter; L709,
L710, C742, C744−C748), then applied to the antenna via
the ANT UNIT.
4-2-4 APC CIRCUIT (PA-C UNIT)
The APC (Automatic Power Control) circuit prevents the
transition of the transmit output power level which is caused
by load mismatching or heat effect, etc.
A portion of transmit signal is detected by the transmit power
detector (D702) to produce a DC voltage corresponding to the
transmit output power level. The detected voltage is applied to
the APC amplifi er (IC701, pin 3). The transmit power setting
voltage “APC (T1)” from the D/A converter (MAIN-C UNIT;
IC23, pin 1) is applied to another input terminal (pin 1) as the
reference voltage.
The APC amplifier compares the detected voltage and
reference voltage, and the difference of the voltage “APCV” is
output from pin 4. The voltage “APCV” controls the bias of the
drive (Q702) and power (Q701) amplifi ers to reduce/increase
the gain of these amplifi ers for stable transmit output power.
The transmit power muting is carried out by the TX mute switch
(MAIN-C UNIT; Q46), using the “TMUT” signal from the CPU
(IC22, pin 35).
4 - 3
Power
amp.
APC
amp.
Drive
amp.
+
1
3
4
–
VCC
MAIN-C UNIT
• APC CIRCUIT
to the anntena
“APC (T1)”
“TMUT”
from TX/RX switch
(MAIN-C UNIT; D16, D17)
T5V
Q702
Q703, Q704
IC701
Q701
to the receive circuits
LPF
LPF
LPF
ANT
SW
D702
D701, D704
Transmit
power detecter
Q46
Pre-drive
amplifiers
Summary of Contents for IC-F4029SDR
Page 3: ...SERVICE MANUAL ADDENDUM CONTENTS PARTS LIST 1 BOARD LAYOUTS 7 VOLTAGE DIAGRAM 9 Jul 2006 ...
Page 13: ... iC f4029sdr S 14228MZ C1 Apr 2006 UHF TRANSCEIVER ...
Page 18: ...2 1 SECTION 2 INSIDE VIEWS ...
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Page 41: ...9 1 SECTION 9 BOARD LAYOUTS ...
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Page 43: ...10 1 SECTION 10 BLOCK DIAGRAM ...
Page 44: ...11 1 SECTION 11 VOLTAGE DIAGRAM ...
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Page 48: ...1 1 32 Kamiminami Hirano ku Osaka 547 0003 Japan S 14228MZ C1 2006 Icom Inc ...