Signal Strength Meter Circuit; Agc Circuit; Squelch; If Filter - Kenwood TK-80 Service Manual

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
CIRCUIT DESCRIPTION
Q35
Q30
L75
2 6
1 7
– –
+ +
3 IC2 (1/2) 5 IC2 (2/2)
+
10
VR6
12
11
+
+
AGS
Fig. 6 S-meter and AGC circuits
10.695MHz Part No./
filter name
AM L71-0433-15
SSB-WIDE L71-0457-05
(Option) /KIF-1
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
Q33
Q31
Q38
9
IC1
6
+
8
+
AMB SM
Contorl unit
Selection of each mode
DATA DATA
CW SSB AM
(AFSK) (FSK)
- - -
- - -
✳
-
✳ - - -
OUT/IN
OUT/IN
SSB/SSB-W/AM/CW
AFSK/FSK
D54
D52
L76
D53
CAR Detector
10.695MHz OUT
-
✳
✳