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TK-80
3-3. Signal strength meter circuit
In all mode, the signal strength meter circuit comprises
operational amplifier IC2. The signal level detected is input to
pin 3 of IC2 (1/2) and amplified by about 8dB by IC2 (2/2), then
goes to IC5 of the control unit (Fig. 6).
3-4. AGC circuit
The time constant for the signal envelope detected by IC1
is changed in each mode by the analog switch. The effective
value, not the peak value, is used in AM mode (Fig. 6).
3-5. Squelch
The squelch volume voltage is input to A/D input pin 78 of
the CPU IC5. The signal strength meter voltage made by
squelch volume voltage and the TX-RX unit is compare pro-
cessed in the CPU, controlling the ABK signal.
3-6. IF filter
There are two internal 10.695MHz IF filters and two op-
tional, so a total of four can be installed.
8V
SSB, AM, CW
2nd IF IN
RXC
14
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CIRCUIT DESCRIPTION
Q35
Q30
2
6
–
1
–
+
+
5
3
IC2 (1/2)
IC2 (2/2)
+
VR6
12
AGS
Fig. 6 S-meter and AGC circuits
manuals search engine
10.695MHz
Part No./
filter
AM
L71-0433-15
SSB-WIDE L71-0457-05
(Option)
SSB
L71-0249-05
CW
L71-0283-15
(Option)
/YK-107C
represents the initial set value
✳ represents selections which can be used when the op-
tional filter is attached
DATA (AFSK): SSB+DATA display
DATA (FSK): DATA display
Also, filter selection and DATA key settings are switched
in the following dealer mode menu.
CH.02: CW FILTER
CH.03: DATA (AFSK)-SSB WIDE FILTER
CH.15: DATA (FSK)-IF FILTER FOR
CH.14: DATA MODE
D55
Q31
L75
Q38
7
10
9
IC1
6
+
11
8
+
+
+
AMB
SM
Contorl unit
Selection of each mode
name
CW
SSB
AM
-
-
-
-
-
/KIF-1
-
✳
-
-
OUT/IN
OUT/IN
SSB/SSB-W/AM/CW
AFSK/FSK
D54
Q33
L76
CAR
10.695MHz
DATA DATA
(AFSK) (FSK)
-
-
✳
✳
-
✳
D52
D53
Detector
OUT
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