Kenwood TH-K2AT Service Manual page 13

CTCSS/ DCS
The encode signal is generated by the M PU (IC8) and output
from the TONE terminal (pin 41) of the M PU.
The unw anted high-frequency components of the encode
signal output from the M PU are removed w ith a low -pass filter,
and applied to VCO modulation input (M OD) 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
M PU after the w aveform of the audio signal from the FM IC is
rectified w ith a CTCSS/DCS filter (IC17). Then the set CTCSS
tone frequency and DCS code are detected by digital signal
processing in the M PU to control muting.
X1
TCXO
VC
VR6
M OD
VCO
VOL OUT
IC6
AF AM P
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, w hen communicating w ith a personal
computer.
CIRCUIT DESCRIPTION
LPF
Q30 D24
50
AM P
1
M IC
IC16
AM P
6
M IC
IC5
HPF
Fig. 15 CTCSS/ DCS, DTM F, VOX, Weather alert
M IC JACK
TH-K2AT/K2E/K2ET
DTM F
The DTM F signal is generated by the M PU (IC8) and is
output from the DTM F/BEEP terminal (pin 40) of the M PU.
The DTM F signal is mixed w ith an audio signal at the input
side of the AF amplifier (IC6), and is output as a monitor tone.
The DTM F signal is mixed w ith 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 M PU (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 M PU (IC8) processes the signal. This signal processing
activates Weather Alert function.
41
TONE IC17
47
CTCSS/DCS
VOX IN SIG IN
FILTER
IC8
111
M PU
NOAA K, K2 types only
DTM F/BEEP
40
5M C
IC5
HPF
PTT
M IC
IM
J3
5M S
SPG
REM /TXD
J4
SPK
SP JACK
AFO
10
SP
Fig. 16 Serial control
IC3
9
FM
IC
+
M IC
–
13
PTTE
46
REM
TXD
IC8
POUT
RXD
M PU
IC6
AF AM P
12
11
13