Kenwood TK-760G Service Manual page 26

TK-760G/ ( N
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. 6 Unlock circuit
MIC IC507(1/2) IC508
AF AMP,
AF AMP
IDC, LPF
NJM2904V
TC35453F
IC502
CPU
MIC KEY
30622M
INPUT
4XXXGP
26
) /762G/ ( N )
CIRCUIT DESCRIPTION
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. 7 Transmitter system
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.
APC Circuit
The automatic transmission power control (APC) circuit
detects part of a power module output with a diode (D35,
D36) and applies a voltage to IC15. IC15 compares the APC
control voltage (PC) generated by the D/A converter (IC6)
and DC amplifier (IC7) with the detection output voltage to
control Q31 and Q32, generates DB voltage from B voltage,
and stabilizes transmission output.
The APC circuit is configured to protect over current of
the power module due to fluctuations of the load at the an-
tenna end and to stabilize transmission output at voltage
and temperature variations.
Q22 Q25
RF RF
D16
AMP
AMP
Q33
TEMP
PROTECT
IC7
PC
DC
IC6
AMP
23pin
Fig. 8 APC circuit
Q106 IC8 Q14
BUFFER 1/2 BUFFER
2SC4226 DIVIDER 2SC4649
(R24) UPB1509GV (N,P)
Q9
BUFFER
2SC4215
(Y)
IC400 D34
POWER ANT
LPF
AMP SW
DB
Q32
D35,36
APC POWER
+B
DRIVER DET
Q31
PRI
DRIVER
IC15
APC
CONTROL
Q22 Q25 IC400
RF AMP RF AMP POWER AMP
2SC3357 2SC2954 M67741H-32
ANT
ANT