Transmitter System; Unlock Circuit; Power Amplifier Circuit - Kenwood 762G Service Manual

TK-760G/762G
IC3 : PLL IC
PLL
DATA
16.8MHz

Unlock Circuit

During reception, the 8RC signal goes high, the 8TC sig-
nal goes low, and Q16 turns on. Q18 turns on and a voltage
is applied to the collector (8R). During transmission, the
8RC signal goes low, the 8TC signal goes high and Q29
turns on. Q28 turns on and a voltage is applied to 8T.
The CPU in the control unit monitors the PLL (IC3) LD
signal directly. When the PLL is unlocked during transmis-
sion, the PLL LD signal goes low. The CPU detects this
signal and makes the 8TC signal low. When the 8TC signal
goes low, no voltage is applied to 8T, and no signal is trans-
mitted.
8R
LD
IC3 IC502
PLL CPU
PLL lock
: LD "H"
CONTORL UNIT
Fig. 7 Unlock circuit
MIC IC507(1/2) IC508
AF AMP,
AF AMP
IDC, LPF
NJM2904V
TC35453F
IC502
CPU
MIC KEY
30622M
INPUT
4XXXGP
26
CIRCUIT DESCRIPTION
5kHz/6.25kHz
1/N
Phase Charge
comparator pump
REF
OSC
1/M
5kHz/6.25kHz
Fig. 6
8C
Q18 Q28
8T
SW SW
Q16 Q29
SW SW
8RC
8TC
IC9
SHIFT
REG.
IC6 Q103
D/A VCO
CONVERTER 2SK508NV
M62363FP (K52)
IC1 X1 IC3
SUM AMP VCXO PLL
TA75S01F 16.8MHz MB15A02
Fig. 8 Transmitter system
PLL/VCO
Q103
TX VCO
LPF
D102,104
Q101
RX VCO
D101,103
PLL circuit

Transmitter System

Outline
The transmitter circuit produces and amplifies the de-
sired frequency directly. It FM-modulates the carrier signal
by means of a varicap diode

Power Amplifier Circuit

The transmit output signal from the VCO is amplified to a
specified level of the power module (IC400) by the drive
block (Q22 and Q25). The amplified signal passes through
the transmission/reception selection diode (D16) and goes
to a low-pass filter. The low-pass filter removes unwanted
high-frequency harmonic components, and the resulting sig-
nal is goes the antenna terminal.
Q106 IC8 Q14
BUFFER 1/2 BUFFER
2SC4226 DIVIDER 2SC4649
(R24) UPB1509GV (N,P)
Q9
BUFFER
2SC4215
(Y)
Q9
RF AMP
Q106
BUFF
AMP
Q102,
104,105
T/R SW
Q22 Q25 IC400
POWER AMP
RF AMP RF AMP
M67741H-32 : K,M
2SC3357 2SC2954
M67741L-35 : K2
ANT