Kenwood FM Transceiver TK-481 Service Manual page 20

7-2. Decode
• Low-speed data (QT,DQT,LTR)
The demodulated signal from the IF IC (IC9) is amplified
by IC8 (1/2) and passes through a low-pass filter (IC10) to
remove audio components. The signal is input to pin 23 of
the CPU.
The CPU digitizes this signal, performs processing such
as DC restoration, and decodes the signal.
• High-speed data (DTMF)
The DTMF input signal from the IF IC is amplified by IC8
(1/2) and goes to IC13, the DTMF decoder. The decoded in-
formation is then processed by the CPU. During transmis-
sion and standby, the DTMF IC is set to the power down
mode when the PD terminal is High. When the line is busy,
the PD terminal becomes Low, the power down mode is
canceled and decoding is carried out.
• MSK
The MSK input signal from the IF IC is amplified by IC8 (1/
2) and goes to pin 5 of IC12. The signal is demodulated by
MSK demodulator in IC12. The demodulated data goes to
the CPU for processing.
IC8 IC10
AMP LPF
IC13
DTMF
DECODE
IC12
OSC1
XOUT
PD
Fig. 13 Decode
8. Power Supply Circuit
Battery +B is supplied via a 3A fuse from the battery ter-
minal connected to the TX-RX unit. After passing through
the power switch, power supply (SB) is applied to the three
AVRs. IC5 supplies 5V (5M) to the control circuit, and IC7
supplies 5V (5C) to common circuits. IC6 supplies to the TX
circuit and the RX circuit. During transmission, 5TC be-
comes Low and Q2 is turned ON to supply 5V (5T) to the TX
circuit. During reception, 5RC becomes Low and Q1 is
turned ON to supply 5V (5R) to the RX circuit.
CIRCUIT DESCRIPTION
23 LSD
IN
IC15
CPU
DCK,SD,STD
7
IC19
TK-480/481
F1
+B
SB
ON/OFF
VOL
Display unit
Fig. 14 Power supply circuit
9. Optional Board Terminal
Terminals for mounting the option board are provided at
the bottom edge of the TX-RX unit. The table below shows
the correspondence between the board and terminals.
R422, R32, R250, R259, R147, R276, R421 may have to be
removed depending on the type of option board being used.
Name
SB Battery (7.5V)
GND Ground
TXD Serial data
RXD Serial data
SQ Busy: high
LOK Link acquired : low (TX mode)
DI/ANI Modulation (ANI) input
DEO Detect output
TXAI/MUTE Modulation output from board or mic mute: low
TXAO Modulation input to board
RXAI Received signal input to board
RXAO Received signal output from board
D1 Binary 1
D2 Binary 2
OPT Scramble, Emergency: low
PTTIN PTT switch signal input to board (TX: low)
5CNS Battery (5V)
DI9 9600 bps data output
RXEMAO Received signal output from board (after de-emphasis)
RXEMAI Received signal input to board (after de-emphasis)
PTTOUT PTT switch signal output from board (TX: low)
MONI Busy: low
LAMP Busy: low
AAC Audio Amp Control signal output from board (Busy: high)
Audio Beep Beep signal output from board
AUX TXD Serial data
AUX RXD/EXTSW Serial data/Option switch port
Table 1 Terminal name and function
RF power amp (IC30)
IC5
5M
IC7 5C
Q2
IC6 5T
5TC
5R
Q1
5RC
Function
19