Kenwood TH-K4AT Service Manual page 13

CTCSS/DCS
The encode signal is generated by the MPU (IC8) and output
from the TONE terminal (pin 41) of the MPU.
The unwanted high-frequency components of the encode
signal output from the MPU are removed with a low-pass filter,
and applied to VCO modulation input (MOD) and TCXO VC
terminal for modulation.
The VCO and TCXO modulation levels are adjusted by VR6
to produce flat modulation characteristics in low and high
ranges.
The decode signal is input to the SIGIN pin (pin 47) of the
MPU after the waveform of the audio signal from the FM IC is
rectified with a CTCSS/DCS filter (IC17). Then the set CTCSS
tone frequency and DCS code are detected by digital signal
processing in the MPU to control muting.
MOD
VCO
Serial Control
Serial control must be enabled from a transceiver menu so
that the REM/TXD pin of the speaker jack (J4) and the PTT
(RXD) pin of the microphone jack (J3) function as TXD and
RXD, respectively, when communicating with a personal
computer.
CIRCUIT DESCRIPTION
X1
TCXO
VC
LPF
VR6
1
MIC
IC16
AMP
6
IC5 MIC
VOL OUT
IC6
HPF
AF AMP
Vin
Fig. 15 CTCSS/DCS and DTMF, VOX
TH-K4AT/K4E
DTMF
The DTMF signal is generated by the MPU (IC8) and is
output from the DTMF/BEEP terminal (pin 40) of the MPU.
The DTMF signal is mixed with an audio signal at the input
side of the AF amplifier (IC6), and is output as a monitor tone.
The DTMF signal is mixed with a modulation signal at the
input side of pre-emphasis in the microphone amplifier (IC16)
and used as a transmit signal.
VOX
The IC5 and Q30 amplify the audio signal captured in the
microphone, and then the signal is converted into the DC
Voltage D24 rectifies.
The DC voltage activates the MPU (IC8), and the VOX starts.
41
Q30 D24 TONE
50
AMP VOX IN SIG IN
IC8
MPU
DTMF/BEEP
40
5MC
IC5
HPF
PTT
MIC
IM
J3
MIC JACK
5MS
SPG
REM/TXD
J4
SPK
SP JACK
AFO
SP
Fig. 16 Serial control
IC17 IC3
47 9
CTCSS/DCS FM
FILTER IC
+
MIC
–
13
PTTE
46
REM
10
IC8
POUT
MPU
IC6
AF AMP
12
TXD
11
RXD
13