TM-271A/271E
4
■
Unlock Circuit
During reception, the 8RC signal goes high, the 8TC signal
goes low, and Q34 turns on. Q33 turns on and a voltage is
applied to 8R. During transmission, the 8RC signal goes low,
the 8TC signal goes high and Q36 turns on. Q35 turns on and
a voltage is applied to 8T.
The CPU monitors the PLL (IC401) LD signal directly.
When the PLL is unlocked during transmission, 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 transmitted. (See Fig. 7.)
IC101
CPU
Q34
SW
Q33
SW
IC401
PLL
Q36
SW
Q35
SW
LD
8RC
8C
8R
8T
8TC
PLL lock
: LD “H”
Fig. 7
Unlock 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 (D409) 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 transmitted through the
antenna terminal. (See Fig. 8.)
■
APC Circuit
The automatic transmission power control (APC) circuit
detects part of a final amplifier output with a diode (D606,
D607) and applies a voltage to IC501. IC501 compares the
APC control voltage (PC) generated by the D/A converter
(IC161) and DC amplifier (IC203) with the detection output
voltage. IC501 generates the voltage to control Q503 and
Q504 and stabilizes transmission output.
The APC circuit is configured to protect over current of
Q503 and Q504 due to fluctuations of the load at the antenna
end and to stabilize transmission output at voltage and tem-
perature variations. (See Fig. 9.)
RF
AMP
Q501
DRIVE
AMP
Q503
FINAL
AMP
Q504
PRE
DRIVE
AMP
Q502
DC
AMP
IC203
ANT
SW
D602,D603
D605
LPF
ANT
POWER
DET
D606
D607
IC501
VR601
APC
CONTROL
D409
IC161
(PC/TVO)
(PC)
Q411
RF AMP
Q501
RF AMP
Q502
PRE
DRIVE AMP
Q503
ANT
DRIVE
AMP
Q504
FINAL
AMP
IC402
1/2
DIVIDER
IC161
Q406
D/A
CONVERTER
D/A
CONVERTER
D/A
CONVERTER
X401
TCXO
16.8MHz
VCO
IC401
PLL
Q410
BUFFER
Q404
RF AMP
IC203
BUFFER
IC101
IC161
MIC KEY
INPUT
CPU
IC161
IC203
SUM
AMP
IC202
IC201
MIC
MIC/IDC
SPLATTER
FILTER
Fig. 9
APC circuit
Fig. 8
Transmitter system
CIRCUIT DESCRIPTION
