Kenwood TK-7160 Service Manual page 14

TK-7160
■ Unlock Circuit
During reception, the 8RC signal goes high, the 8TC signal
goes low, and Q44 turns on. Q43 turns on and a voltage is
applied to the collector (8R). During transmission, the 8RC
signal goes low, the 8TC signal goes high and Q46 turns on.
Q45 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.
Q43
8R
SW
Q44
SW
8RC
Fig. 7 Unlock circuit
MIC IC211
MIC/
IDC
MIC KEY
INPUT
IC201
D/A
CONV.
TCXO
16.8MHz
X401
14
CIRCUIT DESCRIPTION
8C
Q45
8T
SW
Q46
SW
8TC
LD
IC101 IC401
CPU PLL
PLL lock
: LD "H"
IC213 IC241
AQUQ
SW
IC
D/A
CPU
CONV.
IC101 IC201
Q444 Q446 IC402
1/2
TX
BUFF
DIVIDER
VCO
RF
PLL
AMP
IC401 Q431
Fig. 8 Transmitter system
Q501 Q502
PRE
RF
D448 DRIVE
AMP
AMP
IC214
PC
DC
IC201
AMP
3pin
Fig. 9 APC circuit
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 (D448) and ampli-
fied by 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 harmonic com-
ponents, and the resulting signal is goes the antenna termi-
nal.
■ APC Circuit
The automatic transmission power control (APC) circuit
detects part of a final amplifier output with a diode (D606,
D607 and D608) and applies a voltage to IC651. IC651 com-
pares the APC control voltage (PC) generated by the D/A con-
verter (IC201) and DC amplifier (IC214) with the detection
output voltage. IC651 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.
Q447 Q501 Q502
PRE
RF RF
DRIVE
AMP AMP
AMP
D602
Q503 Q504 D603,D605
DRIVE FINAL ANT
SW
AMP AMP
D606
D607
IC651
D608
VR1
APC
CONTROL
ANT
Q503 Q504
DRIVE FINAL
AMP AMP
ANT
LPF
POWER
DET