Base Band Circuit; Transmit Signal Amplification Circuit; High-Frequency Signal Switch Circuit; Apc Circuit - Kenwood TK-5210 Service Manual

(Q407) adjusts the signal path so that the audio signal is input
to the CODEC through the scrambler board.
The audio signal is input to the CODEC (base band circuit)
through the above path.

4-2. Base Band Circuit

The base band circuit of the transmitter system consists
of the following:
• CODEC (IC406)
• DSP (IC411)
• LPF (IC407)
• Buffer (IC409)
• DAC (IC411)
• Amplifier (IC412)
The audio signal output from the base band circuit is
converted to digital data of a sampling frequency of 48 kHz
and a quantization resolution of 16 bits by the CODEC
(IC406). This digital data is sent to the DSP (IC8), and voice
signals of 300 Hz or lower and frequencies of 3 kHz or higher
are cut off and an audio range 300 Hz to 3 kHz 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 CODEC. In APCO
mode, the audio signal is converted to the C4FM base band
signal and output from the CODEC. The DTMF and MSK base
band signals are also generated by the DSP and output by the
CODEC.
LPF (IC407) removes quantization noise from the base
band signal output from the CODEC.
The buffer (IC409) sets the base band signal level to the
DAC input range.
The DAC (IC411) assigns the base band signal to the VCO
(Q311) and VCXO (X301).
At this time, the level output according to the transmit
carrier is fine-adjusted according to the modulation method
of FM Wide, FM Narrow and APCO.
EXT.MIC
MIC(MAIN)
IC603
MIC(SUB)
N/C
AMP
MSW/CTS
MM
4-6. Temperature Protection Circuit
The temperature protection circuit reduces the APC
voltage when the temperature of Q105 rises, to prevent
thermal destruction of the final amplifier (Q105). The CPU
D101
T/R SW
CIRCUIT DESCRIPTION
D402,D403
DET
MIC
Q410 Q406
AGC-AMP
SW SW
IC405
LPF
Fig. 6 Audio band and Base band circuit
Q101 Q102
Q103
Pre Pre Pre
Drive Amp
Drive Amp Drive Amp
3dB
Attenuator
Fig. 7 Transmitter circuit

4-3. Transmit Signal Amplification Circuit

(From T/R switch to Final amplifier)
The transmit signal passing through the T/R switch
(D101) is amplified to approx. 50 mW by the two transistor
amplification circuits (Q101, Q102). The transmit signal
output from Q102 passes through a 3dB attenuator to
improve high-frequency signal matching is amplified by the
drive amplifier (Q103) and applied to the final amplifier
(Q105). The signal applied to the final amplifier is amplified by
the final amplifier so that the antenna output is 5 W (1 W for
Low Power).

4-4. High-Frequency Signal Switch Circuit

(From Antenna switch to ANT output)
The transmit signal output from the final amplifier (Q105)
passes through the antenna switch (D106, D107) and LPF,
and goes into the SPDT switch (IC102, IC103) which changes
the antenna connector (CN101) and the universal connector
(CN102).
The transmit signal passing through the output change
switch passes through the surge protection HPF and
spurious removing LPF and then goes to the antenna
connector (CN101) or the universal connector (CN102),
specified by the SPDT switch (IC102, IC103).

4-5. APC Circuit

The APC circuit detects the current of the drive amplifier
(Q103) and final amplifier (Q105) during transmission and
controls the output power by controlling the current.
It detects the current using R119 and R120 and applies a
drop voltage between both resistors during transmission to
APC (IC101). It controls the transmission current of the drive
amplifier and final amplifier so that it is constant by
comparing this current with the reference voltage output
from pin 7 of IC104. The reference voltage input to pin 5 of
IC104 is output from the DAC (IC411). High/Low power
output is set according to the DAC output voltage.
Scrambler board
Q407 IC8
SW DSP
IC406 IC407 IC409
CODEC LPF BUFF
SCSW
(IC5) detects the temperature with a thermistor (TH101) to
control the reference voltage to the APC circuit.
IC102,IC103
Q105
SPDT
Final Amp D106,D107
ANT SW
LPF
IC101
R119 R120
APC
APC SW
+B
TK-5210
Q311
IC411
VCO
DAC
IC412 X301
AMP VCXO
CN101
CN102
15