38
TK-782
Fig. 7 Unlock circuit /
"
Unlock Circuit
During reception, the TR signal goes high, the KEY signal
goes low, and Q10 turns on. Q11 turns on and a voltage is
applied to the collector (8R). During transmission, the TR
signal goes low, the KEY signal goes high and Q13 turns on.
Q12 turns on and a voltage is applied to 8T.
The CPU in the TX-RX unit (B/2) monitors the PLL (IC300)
LD signal directly. When the PLL is unlocked during trans-
mission, the PLL LD signal goes low. The CPU detects this
signal and makes the KEY signal low. When the KEY signal
goes low, no voltage is applied to 8T, and no signal is trans-
mitted.
"
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
(Q203, Q204). The amplified signal passes through the trans-
mission/reception selection diode (D211) and goes to a low-
pass filter. The low-pass filter removes unwanted high-fre-
quency harmonic components, and the resulting signal is
goes the antenna terminal.
"
APC Circuit
The automatic transmission power control (APC) circuit
detects part of a power module output with a diode (D27,
D30) and applies a voltage to Q21. Q21 compares the APC
control voltage (PC) generated by the D/A converter (IC5) and
DC amplifier (IC6) with the detection output voltage to con-
trol Q19 and Q20, generates DB voltage from B voltage, and
stabilizes transmission output.
Q17 turns the PC signal on or off using 8T so that the
circuit works only during transmission. With stability at low
power in mind, Q29 turns off to optimize the detection volt-
age.
The APC circuit is configured to protect overcurrent of the
power module due to fluctuations of the load at the antenna
end and to stabilize transmission output at voltage and tem-
perature variations.
"
"
"
IC508
SHIFT
REG.
IC511
CPU
Q10
SW
Q11
SW
IC300
PLL
Q13
SW
Q12
SW
LD
TX-RX UNIT (B/2)
TR
8C
8R
8T
KEY
PLL lock
: LD H
CIRCUIT DESCRIPTION /
Fig. 8 APC circuit /
RF
AMP
Q203
RF
AMP
Q204
POWER
AMP
IC400
APC
DRIVER
Q19
DB
+B
VR1
Q20
PRI
DRIVER
DC
AMP
IC6
PC
SW
Q17
ANT
SW
D211
LPF
ANT
Q29
POWER
DET
D27,30
Q21
APC
CONTROL
H/L
SW
H/L
IC7 5pin
25W (High power)
: H
8T
(TX : 8V)
TX :
PC SW ON
D15
PC
IC5
23pin
Summary of Contents for TK-782
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