Kenwood TK-5210G Service Manual page 20

TK-5210
3-6. Squelch Circuit
It amplifies the demodulated noise signal from FM IC
(IC204) after fi ltering through BPF circuit. Then, the ampli-
fi ed signal is converted to DC signal by the detection circuit.
The converted signal is fed to the ASIC (IC10).
4. Transmitter System
4-1. Audio Band Circuit
The signal from the microphone passes through the
mute switch (Q506) and AGC circuit (IC516, D511, D512,
Q504, Q505), and goes to the summing amplifi er (IC513),
then is fed into ASIC (IC10) and converted from analogto
digital. The digitalized signal undergoes AGC processing,
pre-emphasizing, fi ltering, vocording (in APCO mode), and
returns to the ASIC (IC10). The signal is converted from digi-
tal to analog signal is amplifi ed by ASIC (IC10). Then the sig-
nal adjusted to appropriate level passes through the buffer
(IC512) and DAC (IC502), and goes to the VCO and VCXO in
PLL section.
20
( G )
CIRCUIT DESCRIPTION
EXT. MIC
INT. MIC Q508 Q506
SW SW
Q507 SW
CTS0_univ MM
IC512 IC502
LPF DAC
Fig. 6 Audio band and Base band circuit
IC204
FM IC
4-2. Base Band Circuit
The audio signal output from the base band circuit is con-
verted to digital data of a sampling frequency of 48kHz.
This digital data is sent to the DSP (IC3), and voice sig-
nals 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 re-
quired, and is then output from the ASIC (IC10). In Digital
mode, the audio signal is converted to the C4FM base band
signal and output from the IC10. The DTMF and MSK base
band signals are also generated by the DSP and output by
the IC10.
LPF (IC512) works as smoothing fi lter. The DAC (IC502)
assigns the base band signal to the VCO and VCXO (X301).
At this time, the level output according to the transmit car-
rier is fi ne-adjusted according to each modulation method.
Optional Scrambler Board
IC516 IC515 IC513
AMP SW
AGC
D511,D512
Q504,Q505
/SCSW
IC500 X301
AMP VCXO
VCO
Q502 D500
Noise
DET
AMP
Fig. 5 Squelch circuit
IC3
DSP
IC10
AMP
ASIC
IC10
ASIC