28
TK-690H
(
B
)
6-3. D/A converter
IC512 is used as a conventional semi-fixed-resistor con-
verter. It sets the following :
1) RX sensitivity
2) Transmission power
3) Modulation level
4) Audio power
5) Frequency
6-4. Power supply circuit
D507 is a protection diode for the excess voltage.
1) Turning the transceiver on/off with a power switch. Each
time you press the power switch, the IC501 output is al-
ternated. The output is feed through Q501, Q503 to turn
Q519 on. The power source is always supplied to the
IGN terminal. If 24V DC is supplied to the transceiver by
mistake, Q502 is turned on then Q503 and Q519 are
turned off to protect the transceiver (turned off).
2) Turning the transceiver on with a power switch, then
turning the transceiver off with the Timed Power Off
(TPO) function. POF is controlled by CPU’s TPO function.
POF is to turn the transceiver off. The POF logic signal is
feed through Q507 and Q506 then 8 pin of IC501 to turn
the transceiver off.
3) Turning the transceiver on with IGN SENS, then turning
the transceiver off with TPO function. If IGN is turned on,
Q543 and Q542 are turned on then the IC501 detects the
change. IC501 outputs the signal to turn Q541 off, then
Q503 and Q519 are turned on. When POF is detected by
6 pin of IC501, Q541 is turned on then Q503 and Q519
are turned off.
CIRCUIT DESCRIPTION
D507
AVR
Q506
SW
Q543
SW
Q542
SW
Q544
SW
Q503
SW
Q519
SW
IC501
D-FF
Q501
SW
D501
SW
Q502
SW
Q541
SW
Q507
SW
Q518
SW
IGN
+B
POF
PS
SB
Fig. 8
Power supply circuit
7. Signalling Circuit
7-1. Encode
• QT, DQT
The CPU (IC516) transmits the encode data selected by
the program. The data items are output from CPU pin 34.
The signal from this pin passes though the CR low-pass
filter and goes to the summing amplifier (IC510) in the mi-
crophone amplifier.
• DTMF
The DTMF-encoder (IC511) transmits the encode data.
The encode data is passed to the D/A convertor (IC512) for
DTMF deviation adjustment, and goes to IC505 in the IDC
circuit of the microphone amplifier.
7-2. Decode
• QT, DQT
The demodulated signal from CN502 pin 5 is amplified by
IC521 and passes through a low-pass filter (IC502) to re-
move audio components. The signal is input to pin 25 of the
CPU. The CPU digitizes this signal, and decodes the signal.
• 2 TONE
The demodulated signal from CN502 pin 5 is amplified by
IC504 and passes through a high-pass filter (IC518) and a
band-elimination filter (IC524) to remove QT and DQT.
This signal is amplified by IC521 and inputs pin 91 of the
CPU.
• DTMF
The demodulated signal from CN502 pin 5 is amplified by
IC504 and passes through a high-pass filter (IC518) and
band-elimination filter (IC524) to remove QT and DQT.
This signal inputs pin 1 of the DTMF decoder (IC525).
CN502
DET
5
IC504
AMP
IC521
AMP
IC518
HPF
IC502
LPF
IC524
BEF
IC502
LPF
IC525
DTMF
decoder
IC521
AMP
1
25
91
QT·DQT
2TONE
SD
IC516
CPU
Fig. 9
Decode
Содержание TK-690B
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