Kenwood TK-8102 Service Manual page 18

TK-8102
■ Unlock Circuit
During reception, the 8RC signal goes high, the 8TC signal
goes low, and Q34 turns on. Q33 turns on and a voltage is
applied to the collector (8R). During transmission, the 8RC
signal goes low, the 8TC signal goes high and Q36 turns on.
Q35 turns on and a voltage is applied to 8T.
The CPU in the control unit monitors the PLL (IC401) LD
signal directly. When the PLL is unlocked during transmis-
sion, the PLL LD signal goes low. The CPU detects this sig-
nal and makes the 8TC signal low. When the 8TC signal goes
low, no voltage is applied to 8T, and no signal is transmitted.
Q33
8R
SW
Q34
SW
8RC
Fig. 7 Unlock circuit
MIC IC201
MIC/IDC
NJM2100V
MIC KEY
INPUT
IC161
D/A
CONVERTER 2SK508NV
M62363FP
X401 IC401
TCXO
16.8MHz
18
CIRCUIT DESCRIPTION
8C
Q35
8T
SW
Q36
SW
8TC
LD
IC101 IC401
CPU PLL
PLL lock
: LD "H"
IC202 IC203
Splatter
SUM AMP
FILTER
NJM2902V
NJM2904V
IC161
IC101
CPU D/A
30622MAA CONVERTER
-B87GP M62363FP
Q406 Q410
RF AMP
VCO BUFFER
2SC5108 2SC5108
(K52) (Y)
Q404
RF AMP
PLL
2SC4649
MB15A02
(N,P)
Fig. 8 Transmitter system
Q500 Q501
RF RF
D409
AMP AMP
IC203
PC
DC
IC161
AMP
3pin
Transmitter System
■ Outline
The transmitter circuit produces and amplifies the desired
frequency directly. It FM-modulates the carrier signal by
means of a varicap diode.
■ Power Amplifier Circuit
The transmit output signal from the VCO passes through
the transmission/reception selection diode (D409) and ampli-
fied by Q500, Q501 and Q502. The amplified signal goes to
the power amplifier (IC502) through a low-pass filter. The
low-pass filter removes unwanted high-frequency harmonic
components, and the resulting signal is goes the antenna ter-
minal.
■ APC Circuit
The automatic transmission power control (APC) circuit
detects the power amplifier (IC502) output with a diode
(D606, D607) and applies a voltage to IC501. IC501 com-
pares the APC control voltage (PC) generated by the D/A con-
verter (IC161) and DC amplifier (IC203) with the detection
output voltage. IC501 generates the voltage to control IC502
and stabilizes transmission output.
The APC circuit is configured to protect over current of
IC502 due to fluctuations of the load at the antenna end and
to stabilize transmission output at voltage and temperature
variations.
IC161 IC203
D/A
BUFFER
CONVERTER
NJM2902V
M62363FP
Q411 Q500 Q501
RF AMP
RF AMP
2SC5108
2SC3357
(Y) (Y)
Q502 IC502 D604,D605
RF POWER
AMP
MODULE
Vg
+B
IC501
APC
CONTROL
Fig. 9 APC circuit
Q502 IC502
POWER AMP
RF AMP
RA30H4452M-31 : M,M2
2SC3357
RA30H4047M-31 : M3
ANT
D602
ANT
LPF
SW
POWER
D606
DET
D607
ANT