TK-7160/7162
13
■ 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 and Q502. The amplified signal goes to the RF
power module (IC502) 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
and IC502 and stabilizes transmission output.
The APC circuit is configured to protect over current of
Q502 and IC502 due to fluctuations of the load at the antenna
end and to stabilize transmission output at voltage and tem-
perature 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
RF POWER
MODULE
IC502
PRE
DRIVE
AMP
Q502
DC
AMP
IC214
ANT
SW
D602
D603
LPF
ANT
POWER
DET
D606
D607
D608
IC651
APC
CONTROL
D448
PC
IC201
pin 3
ANT
IC211MIC
MIC/
IDC
IC213
SW
IC101
CPU
Q444
TX
VCO
Q446
BUFF
Q447
RF
AMP
Q501
RF
AMP
Q502
PRE
DRIVE
AMP
IC502
RF POWER
MODULE
IC402
1/2
DIVIDER
PLL
TCXO
16.8MHz
MIC KEY
INPUT
IC241
AQUA
IC
IC201
IC201
D/A
CONV.
D/A
CONV.
X401
IC401
RF
AMP
Q431
CIRCUIT DESCRIPTION
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