Kenwood TK-8102H Service Manual page 11

ANT
L36,38,48,49
D801~
D25,26,28
D804
ANT
SW
IC3
D/A
Wide/Narrow Changeover Circuit
The Wide port (pin 92) and Narrow port (pin 91) of the
CPU is used to switch between ceramic filters. When the
Wide port is high, the ceramic filter SW diodes (D13, D15)
cause CF1 to turn on to receive a Wide signal.
When the Narrow port is high, the ceramic filter SW diodes
(D13, D15) cause CF2 to turn on to receive a Narrow signal.
IF_IN
CF1
(Wide)
CF2
(Narrow)
D13
Narrow
IC6 91pin
Fig. 3 Wide/Narrow changeover circuit
CIRCUIT DESCRIPTION
L30,32
Q26 D21,22 Q21
RF AMP MIX
BPF BPF
TV
1st local
CPU
OSC (VCO/PLL)
Fig. 2 Receiver system
IC5
IF System
MIX_O
R73
Wide
IC6 92pin
R77
D15
CF1 (Wide)
CF2 (Narrow)
XF1 Q19
MCF IF AMP
IC5
IF system
X1 Q6
TCXO X3 multiply
AF Signal System
The detection signal from IF IC (IC5) goes to D/A con-
verter (IC3) to adjust the gain and is output to AF filter (IC10)
for characterizing the signal. The AF signal output from IC10
and the DTMF signal, BEEP signal are summed and the re-
sulting signal goes to the D/A converter (IC3). The AFO out-
put level is adjusted by the D/A converter. The signal output
from the D/A converter is input to the audio power amplifier
(IC101). The AF signal from IC101 switches between the
internal speaker and speaker jack (J1) output.
IC5 IC3
DEO
D/A
IF IC
CONV.
FIg. 4 AF signal system
Squelch Circuit
The detection output from the FM IF IC (IC5) passes
through a noise amplifier (Q18) to detect noise. A voltage is
applied to the CPU (IC6). The CPU controls squelch accord-
ing to the voltage (SQIN) level. The signal from the RSSI pin
of IC5 is monitored. The electric field strength of the re-
ceive signal can be known before the SQIN voltage is input
to the CPU, and the scan stop speed is improved.
IC5
AF
IF
SYSTEM
RSSI
Fig. 5 Squelch circuit
TK-8102H
IC3
D/A CONVERTER
DEO
IC10 IC3 IC101
AF D/A
AF PA
Filter CONV.
Q18
NOISE AMP D18 IC6
SQIN
DET
CPU
RSSI
SP
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