PT3600 Service Manual
4
APC
SW
APC
CONTROL
APC FROM MCU
CURRENT
SENSING
POWER SUPPLY
Figure 3.3 APC Circuit Diagram
R525, R523 and R524 are used to test the power amplification
current. IC502A is the sampling amplifier for the power
amplification current. IC502B is the power comparator amplifier.
If the Tx output power is too high, the power amplification
current and IC502A output will increase; IC502B output voltage
will decrease, so the offset voltage added to Q501 and Q502 will
also decrease, which causes the Tx output power to be lowered,
and vice versa. Thus the Tx output power can keep stable under
different working conditions.
MCU can set the power through changing the voltage input to
IC502B.
Tx voice signal processing
MIC signal passes through the internal/external MIC switch
circuit and is sent to pin 11 of U8 (RDA1846) for carrier
modulation.
3.4 Frequency Synthesizer
The 12.8MHz reference frequency signal provided by X603 is
divided by the internal reference frequency divider of U8
(RDA1846), and is then sent to the internal phase comparator of
U8, where the signal is compared with the signal divided by the
fractional frequency divider of internal VCO. Then the output
signal is used to control the internal VCO, enabling the frequency
to reach the set value.
3.5 Voice Alert Circuit
The radio is provided with voice alert function, which is
especially useful at night or in dark environment.
IC305 is a Flash voice memory chip, which is stored with
voices of channel indication etc. Once the channel selector knob is
switched, the speaker will announce the current channel number.
You can press the preprogrammed “Channel Annunciation” button
to repeat the current channel number.
If Channel Annunciation function is enabled, the speaker will
annunciate the current channel number once the “Channel
Annunciation” button is pressed under standby mode. You can
switch the voice type by pressing and holding the “Channel
Annunciation” button while restarting the radio. Do it repeatedly
to switch the voice type in the order of “Chinese Male-English
Male-Chinese Female-English Female-No Alert”.
3.6 Power Supply
The radio uses 7.4V, 1300mAh Li-Poly battery. The Tx power
amplification circuit (Q501 and Q502) and the Rx audio power
amplifier (U1) directly adopt the battery for power supply. Power
of other circuits is supplied by 3.3V regulated voltage.
Q636, Q639: 3V low dropout, micro-power regulators, which
supply 3V power with large current for the radio together with
Q637.
Q637: 3T switch, which is controlled by MCU.
3T: Supplies power for front end of Tx.
U8: 3C power supply, and supplies power for RD1846.
3.7 MCU Unit
MCU
R8C/2A/2C
7.
3M
Hz
RE
S
E
T
EEPROM
3M
3M
3M
ENCODER
KEYS
KEYAD MODE PTT
SHIFT QTOUT PABC
DTAT CLK LE 3RC
TXD
RXD
AFCO APC MUTE
3TC
QTIN
SQL BATT
W558C
CFA
WDATA WSCLK
G/
R
L
E
D
RD
A
1
84
6
Figure 3.4 MCU Unit Diagram
MCU unit controls the operation of each unit of the radio so
that all functions can be realized.
Communicate with external PC.
Access the status data of the radio.
Control the transmission and reception of RDA1846.
Obtain status parameters of current channel.
Control status of LED indicator.
Control power supply for each unit.
Check the actions of each functional key.
Generate CTCSS signal.
Generate DCS signal.
Generate power control signal.
Perform CTCSS decoding.
Perform DCS decoding.
Test and control the squelch.
Control content of voice alert.
