Kenwood TK-5810 Service Manual page 27

4-2. Base Band Circuit
The audio signal output from the base band circuit is
converted by ASIC (IC708) to digital data of a sampling fre-
quency of 48 kHz. This digital data is sent to the DSP (IC701)
and voice signals of 300Hz or lower and frequencies of
3kHz or higher are cut off and an audio range 300Hz to 3kHz
is extracted. The audio signal is then pre-emphasized in
FM mode and synthesized with the signals, such as QT and
DQT, as required, and is then output from the ASIC (IC708).
In P25 mode, the audio signal is converted to the 4-Level
FSK base band signal and output from the ASIC (IC708).
The DTMF, 2tone and MSK base band signals are also gen-
erated by the DSP (IC701) and output by the ASIC (IC708).
LPF (IC514) works as smoothing fi lter. The DAC (IC517)
assigns the base band signal to the VCO and VCXO (X400).
At this time, the level output according to the transmit car-
rier is fi ne-adjusted according to each modulation method.
4-3. Drive Amplifier Circuit (From T/R switch to
Power module)
The transmit signal passing through the T/R switch (D420)
is amplifi ed by the two drive amplifi ers (Q150 and Q151).
The transmit signal from the drive amplifi er (Q151) passes
through a 3dB attenuator and is fed to the power module.
TX
(CN1)
4-5. Final Amplifi er Circuit (From Power module to
Antenna output): TK-5810H(BG)
The transmit signal from the TX terminal (CN1) of the fi -
nal unit (X45-380) is amplifi ed by the power module (IC1).
The signal amplifi ed by the power module is divided into
two signal, and further is amplifi ed by the fi nal amplifi er (Q1
and Q2). The each signal from Q1 and Q2 is combined.
The combined signal passes through the antenna switch
(D5, D6, D7, D8, D15 and D16), CM coupler and low-pass
fi lter, then it is fed to the antenna.
CM coupler is a line for detecting forward wave and re-
fl ected wave.
CIRCUIT DESCRIPTION
FINAL UNIT (X45-379)
COUPLER
+B
IC2 D5
POWER FWD
MODULE DET
8T
IC1
APC
VR1
PC
Fig. 9 Final amplifi er circuit: TK-5810(BG)
TK-5810
8T
D420
T/R
SW
Drive AMP Drive AMP
Q150 Q151
Fig. 8 Drive amplifi er circuit
4-4. Final Amplifi er Circuit (From Power module to
Antenna output): TK-5810(BG)
The transmit signal from the TX terminal (CN1) of the fi -
nal unit (X45-379) is amplifi ed by the power module (IC2).
The signal amplified by the power module passes
through the CM coupler, antenna switch (D1, D12, D3 and
D11) and low-pass fi lter, then it is fed to the antenna.
CM coupler is a line for detecting forward RF power and
refl ected RF power.
Forward RF power is detected by D5, and is converted
into DC voltage. The converted DC voltage is fed to the APC
comparator (IC1), and is compared with the PC voltage, then
is output from the OUT-B terminal (pin 7) of IC1 as an APC
voltage. The APC voltage controls the gate voltage of the
power module (IC2), and keeps transmission output stable.
If an abnormal antenna load is connected, refl ected RF
power is detected by D6, and output voltage (DC voltage) is
fed to the APC comparator (IC1). The transmission output
is reduced more as this DC voltage rises.
D1,D3,D11,D12 LPF
CM ANT
SW
D6
8T
REFL
DET
Forward wave is detected by D2, and is converted into
DC voltage. The converted DC voltage is fed to the APC
comparator (IC2), and is compared with the PC voltage,
then is output from the OUT-B terminal (pin 7) of IC2 as an
APC voltage. The APC voltage controls the gate voltage of
the power module (IC1) and fi nal amplifi er (Q1 and Q2), and
keeps transmission output stable.
If an abnormal antenna load is connected, refl ected wave
is detected by D3, and output voltage (DC voltage) is fed to
the APC comparator (IC2). The transmission output is re-
duced more as this DC voltage rises.
BG /5810H BG
( ) (
3dB POWER
Attenuator MODULE
ANT
)
27