Kenwood TK-190 Service Manual page 17

7-6. Low battery warning
The battery voltage is monitored by the microprocessor
(IC406). When the battery voltage falls below the voltage
set by the Low Battery Warning adjustment, the red LED
flashes to notify the operator that it is time to replace the
battery. If the battery voltage falls even more (approx. 5.8V),
a beep sounds and transmission is stopped.
Low battery warning
The red LED flashes during
transmission.
The red LED flashes and
continuous beep sounds
while PTT pressed.
8. Signalling Circuit
8-1. Encode
The CPU (IC406) transmits the encode data selected by
the program.
• Low-speed data (QT, DQT)
Low-speed data is output from pin 34 of the CPU. The
signal passes through a low-pass filter consisting of IC413
(2/2), and goes to the summing amplifier (IC605 1/2). The
signal is mixed with the audio signal and goes to the VCO
(L800).
• High-speed data (DTMF)
High-speed data is output from pin 35 of the CPU. The
signal passes through a low-pass filter consisting of IC413
(1/2), and provides a TX DTMF tone and a RX DTMF tone
including a beep tone. The TX DTMF tone is passed to the
D/A convertor (IC603) for DTMF deviation adjustment, and
then applied to the audio processor (IC607).
The signal is mixed with the audio signal and goes to the
VCO. The RX DTMF tone is passed the D/A convertor
(IC603) for audio control summing amplifier (IC604 2/2), au-
dio power amplifier and then to the speaker.
HSD
LPF
OUT
IC406
CPU
LSD
LPF
OUT
SUM
Fig. 12 Encode
CIRCUIT DESCRIPTION
Battery condition
The battery voltage is low, but
the transceiver is still usable.
The battery voltage is low and
the transceiver is not usable to
make calls.
RX AUDIO
to AF AMP
SUM
IC603
DAC SUM
(ADJ)
TX AUDIO
MOD VCO2
8-2. Decode
• Low-speed data (QT, DQT)
The demodulated signal from the FM IC (IC300) is ampli-
fied by IC601 (2/2) and passes through a low-pass filter
(IC602) to remove audio components. The signal is input to
pin 28 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 FM IC (IC300) is ampli-
fied by IC601 (2/2) and goes to IC600, the DTMF decoder.
The decoded information is then processed by the CPU.
During transmission and standby, 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.
• High-speed data (2 tone)
The demodulated signal from the FM IC (IC300) is ampli-
fied by IC601 (2/2) and passes through an audio processor
(IC607) and band-pass filter (IC606) to remove a low-speed
data.
The CPU digitizes this signal, performs processing such
as DC restoration, and decode the signal.
IC601
from IC300
(2/2)
FM IC
AMP
DECODE IC
Fig. 13 Decode
TK-190
IC607 IC606
2TONE IN
AF IC BPF
IC602
LSD IN
LPF
IC406
CPU
IC600
CLOCK,DATA,STD
DTMF
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