RELM RPU416, User Manual, Page: 10 / 39

RPV516/RPU416 Circuit Description
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D
C
B
A
Title
Number Revision Size
AMP
Q101.102
5T
DRIVE AMP
Q105
FINAL AMP
Q107
ANT SW
D101 LPF
ANT
ANT SW
D102.103
RX
Q106
SW
Q109
SW
5T
IC100
APC
DET
Q103.Q104
B SW
B
APC
5T
TH102
SW
Q110
5T
Q108
SW
Fig. 7-b. APC system
5) ANT switch and LPF
The RF amplifier output signal is passed through a low-pass filter network to filter the second
harmonic components and then applied to a transmit/receive switching circuit before it is passed to
the antenna terminal. The transmit/receive switching circuit is comprised of D101, D102 and D103.
D102 and D103 is turned on (conductive) in transmit mode and off (isolated) in receive mode.
6) APC
The automatic power control (APC) circuit stabilizes the transmitter output power at a predetermined
level by sensing the drain current of the final amplifier Field Effect Transistor (FET). The voltage
comparison circuit compares the voltage obtained from the above drain current with a reference
voltage which is set using the microprocessor. The APC voltage is proportional to the difference
between the sensed voltage and the reference voltage output from IC100 (1/2). This output voltage
controls the gate of the FET power amplifier, which keeps the transmitter output power be varied by
the microprocessor which in turn changes the reference voltage and hence, the output power.
7) Temperature protection circuit
When the thermistor (TH102) reaches about 80
℃
, the protection circuit turns on Q110 to protect
transmitting final amplifier (Q107).
5. Power supply
A 5V reference power supply [5M] for the control circuit is derived from an internal battery. This
reference power supply is used to provide a 5V supply in transmit mode [5T], a 5V supply in receive
mode [5R], and a 5V supply common in both modes [5C] based on the control signal sent from the
microprocessor.
6. Control system
The IC403 CPU operates at 7.37MHz. This oscillator has a circuit that shifts the frequency according
to the EEPROM data.