TK-7160
14

■ 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.
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.

Fig. 7 Unlock circuit

IC101
CPU
Q44
SW
Q43
SW
IC401
PLL
Q46
SW
Q45
SW
LD
8RC
8C
8R 8T
8TC
PLL lock
: LD “H”

Fig. 8 Transmitter system

Fig. 9 APC circuit

RF
AMP
Q501
DRIVE
AMP
Q503
FINAL
AMP
Q504
PRE
DRIVE
AMP
Q502
DC
AMP
IC214
ANT
SW
D602
D603,D605
LPF
ANT
POWER
DET
D606
D607
D608
IC651
VR1
APC
CONTROL
D448
PC
IC201
3pin
ANT
IC211MIC
MIC/
IDC
IC213
SW
IC101
CPU
Q444
TX
VCO
Q446
BUFF
Q447
RF
AMP
Q501
RF
AMP
Q502
PRE
DRIVE
AMP
Q503
DRIVE
AMP
Q504
FINAL
AMP
IC402
1/2
DIVIDER
PLL
TCXO
16.8MHz
MIC KEY
INPUT
IC241
AQUQ
IC
IC201
IC201
D/A
CONV.
D/A
CONV.
X401 IC401
RF
AMP
Q431
CIRCUIT DESCRIPTION