TK-385
10
Fig. 13 Decode
IC13
AF IC
IC4
AMP
IC11
LPF
LSD
IN
AF RDT
IN
IC19
CPU
21
23
7-2. Decode
●
Low-speed data (QT,DQT)
The demodulated signal from the IF IC (IC12) is amplified
by IC4 (2/2) and passes through a low-pass filter (IC11) to
remove audio components. The signal is input to pin 95 of the
CPU.
The CPU digitizes this signal, performs processing such as
DC restoration, and decodes the signal.
●
FFSK
The FFSK input signal from the IF IC is amplified by IC4
(1/ 2) and goes to pin 5 of IC13. The signal is demodulated by
FFSK demodulator in IC13. The demodulated data goes to
the CPU for processing.
8. Power Supply Circuit
BB is supplied via a 3A fuse from the battery terminal
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 IC9 supplies 5V
(5C) to common circuits. IC6 supplies to the TX circuit, the RX
circuit and common circuits of needless save mode. During
transmission, 5TC becomes Low and Q3 is turned ON to supply
5V (5T) to the TX circuit. During reception, 5RC becomes Low
and Q2 is turned ON to supply 5V (5R) to the RX Circuit.
Fig. 14 Power supply circuit
Display unit
Q2
5RC
5TC
5R
5T
5CNS
IC6
IC9
IC5
Q3
RF power amp (IC100)
+B
F1
SB
ON/OFF
VOL
5M
5C
CIRCUIT DESCRIPTION
7. Signalling Circuit
7-1. Encode
●
Low-speed data (QT,DQT)
Low-speed data is output from pin 1 of the CPU. The signal
passes through a low-pass CR filter, and goes to the summing
amplifier (IC7 1/2). The signal is mixed with the audio signal
and goes to the VCO (A1) and VCXO (X1) modulation input
after passing through the D/A converter (IC8) for BAL
adjustment.
●
High-speed data (DTMF)
High-speed data is output from pin 2 of the CPU. The signal
passes through a low-pass filter consisting of IC10, and
provides a TX HSD tone and a RX HSD tone TX HSD deviation
making an adjustment by microprocessor is passed through
the D/A convertor (IC8), and then applied to the audio processor
(IC13).
The signal is mixed with the audio signal and goes to the
VCO and VCXO, the RX HSD tone is passed a summing
amplifier (IC7 2/2), the D/A converter (IC8) for audio control,
audio power amplifier and then to the speaker.
●
FFSK
ESN utilizes 1200bps FFSK signal. FFSK signal is output
from pin 6 of IC13. The signal passes through the D/A converter
(IC8) for the FFSK deviation adjustment. and is routed to the
VCO. When encoding FFSK, the microphone input signal is
muted.
Fig. 12 Encode
SUM
SUM
IC7(1/2)
SUM
R166
R162
C175
C169
R137
1
LSD
OUT
HSD
OUT
IC19
CPU
O5
O2
O3
O6
I2
I5
IC8
D/A (ADJ)
VCO
MD
A1
RX Audio
MIC IN
IC13
2
LPF
IC10
I6
I3
VCXO
X1
MB
AF
AMP
IC7 (2/2)
O1 BUFF
AMP
IC1
