Kenwood 144MHz FM TRANSCEIVER K2E 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.
X1
TCXO
VC
VR6
MOD
VCO
VOL OUT
IC6
AF AMP
Vin
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
LPF
Q30 D24
50
AMP
1
MIC
IC16
AMP
6
MIC
IC5
HPF
Fig. 15 CTCSS/DCS, DTMF, VOX, Weather alert
MIC JACK
TH-K2AT/K2E/K2ET
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.
Weather Alert (K and K2 types only)
The IC17 apmlifies the detected signal from the FM IC (IC3),
and the MPU (IC8) processes the signal. This signal processing
activates Weather Alert function.
41
IC17
TONE
47
CTCSS/DCS
VOX IN SIG IN
FILTER
IC8
111
MPU
NOAA K, K2 types only
DTMF/BEEP
40
5MC
IC5
HPF
PTT
MIC
IM
J3
5MS
SPG
REM/TXD
J4
SPK
SP JACK
AFO 10
SP
Fig. 16 Serial control
IC3
9
FM
IC
+
MIC
–
13
PTTE
46
REM
TXD
POUT IC8
RXD
MPU
IC6
AF AMP
12
11
13