Kenwood TK-8108H Service Manual page 16

TK-8108H
■ 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
NJM2904V
MIC KEY
30622MAA
INPUT
IC161 Q406
D/A VCO
CONVERTER 2SK508NV
M62363FP (K52)
X401 IC401
TCXO PLL
16.8MHz MB15A02
16
CIRCUIT DESCRIPTION
8C
Q35
8T
SW
Q36
SW
8TC
LD
IC101 IC401
CPU PLL
PLL lock
: LD "H"
IC202
IC203
Splatter
SUM AMP
FILTER CONVERTER
NJM2902V
M62363FP
IC161
IC101
CPU D/A
CONVERTER
-B83GP M62363FP
Q410 Q411
BUFFER RF AMP
2SC5108 2SC5108
(Y) (Y)
Q404
RF AMP
2SC4649
(N,P)
Fig. 8 Transmitter system
Q500 Q501
PRE
RF
D409 DRIVE
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, Q502 and Q503. The amplified signal
goes to the final amplifier (Q504) through a low-pass filter.
The low-pass filter removes unwanted high-frequency har-
monic components, and the resulting signal is goes the an-
tenna terminal.
■ APC Circuit
The automatic transmission power control (APC) circuit
detects part of a final amplifier (Q504) 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 Q502,
Q503 and Q504 and stabilizes transmission output.
The APC circuit is configured to protect over current of
Q502, Q503 and Q504 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
NJM2902V
Q500 Q501
RF AMP PRE
DRIVE AMP
2SC5110
(O) 2SC3356(R24)
D601,D602
Q502 Q503 Q504 D604,D605
DRIVE DRIVE FINAL
AMP1 AMP2 AMP
IC501
VR1
APC
CONTROL
Fig. 9 APC circuit
Q502 Q503
DRIVE DRIVE
AMP 1 AMP 2
2SK2596 PD55008TR
ANT
ANT
LPF
SW
POWER
D606
DET
D607
ANT
Q504
FINAL AMP
RD60HUF1
-01