TM-471A
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 Q500, 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 har-
monic components, 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 (Q504) output with a diode
(D606, D607) and applies a voltage to IC501. IC501 com-
pares the APC control voltage (PC) generated by the D/A con-
verter (IC161) and DC amplifier (IC203) with the detection
output voltage. IC501 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. (See Fig. 9.)
RF
AMP
Q500
DRIVE
AMP2
Q503
DRIVE
AMP1
Q502
FINAL
AMP
Q504
PRE
DRIVE
AMP
Q501
DC
AMP
IC203
ANT
SW
D601~D605
LPF
ANT
POWER
DET
D606
D607
IC501
APC
CONTROL
D409
IC161
(PC/TVO)
VR601
(PC)
Fig. 9
APC circuit
Fig. 8
Transmitter system
CIRCUIT DESCRIPTION
Q500
RF AMP
RF AMP
Q501
PRE
DRIVE AMP
Q503
ANT
DRIVE
AMP 2
Q502
DRIVE
AMP 1
Q504
FINAL
AMP
Q411
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
