Transmitter Circuit; Apc Circuit - Kenwood TM-V71A Service Manual

TM-V71A/V71E
MIC AMP
IC802
MIC
1/2
Q801
MUTE

3-2. Transmitter Circuit

The VHF VCO output is amplifi ed by RF amplifi er (Q644)
and driver amplifi er (Q131). It is further amplifi ed to the fi nal
output by power module (IC131). The output signal passes
through antenna switch (D134, D135) and a low-pass fi lter,
and is then fed to the antenna.
The UHF VCO output is amplifi ed by RF amplifi er (Q161)
and driver amplifi er (Q162). It is further amplifi ed to the fi nal
output by power module (IC161). The signal passes through
antenna switch (D164, D165), and a low-pass and high-pass
fi lter, and is then fed to the antenna.
6
CIRCUIT DESCRIPTION
ALC AMP
IC802 IC803
IC806
1/2 1/2
Cross
Point
SW
ALC
DTMF
1750Hz
Fig. 5 Modulation circuit
LOCAL
AMP RF AMP
VCO
Q7 Q644
A
LOCAL
AMP RF AMP
VCO
Q72 Q161
B
Fig. 6 Transmitter circuit
IC131 LPF
Power
AMP
VHF
IC161 LPF HPF
Power
AMP
UHF
VSF
to MPU
Fig. 7 APC circuit
PRE-EMPHASIS MOD AMP
IC803
Q805 Q808
2/2
TONE/DCS

3-3. APC Circuit

The Automatic transmission Power Control (APC) circuit
has a differential amplifier (IC187) that compares the DC
voltage generated by detecting part of the transmission
output using diodes (D191, D192) with the reference
voltage output from the D/A IC (IC667). The output signal is
switched by IC186 and is fed to the power module of each
VHF/UHF to keep transmission output constant.
DRIVE
IC131 LPF
AMP
Power
Q131
AMP
VHF
DRIVE
IC161 LPF
AMP
Power
Q162
AMP
UHF
ANT
Reverse
OP AMP
Forward IC187
D192
Analog SW
IC186
D191
FWR REF REV REF
D/A
IC667
IC804
IC807
E VR TCXO (A)
X1
TCXO (B)
X66
VCO (A)
VCO (B)
ANT
HPF
APC V
APC U