Control Unit / Interface Circuit; Power Prime Amplifier; Low Pass Filter; Microprocessor Unit - XIEGU X108G Service Manual

3.2.6 Power prime amplifier

P2 outputs a transmitting small signal, this small signal
is connected to the socket P4B on the power supply
board by IPEX wire, and it is prime amplified by Q5B
(2SC5551), then output by the T6B.
3.2.7 Power amplifier units
Power amplifier units are composed of Q4B 、 Q3B 、
Q1B 、 Q2B. Q1B and Q2B
amplifier ， Push-pull amplifier are made up of 2pcs
RD16HHF1 ， stable output around 18W power signal.
T2B is final stage output transformer.
The bias voltages of each level power tubes are all
generated and supplied by a pedestal generator which
consists of Q7B and U6B.

3.2.8 Low pass filter

The 6 stage, 5th order elliptic low-pass filter which is
composed of relay and magnetic winding is responsible
for filtering and removing the spurious and harmonic
signals which are generated by the power amplifier,
and U3B, U4B and U9B control the band switching.
are final stage power
3.2.9 Power/Standing wave detector
The power/SW detector is composed of T1B, T7B, D1B,
D2B etc. It detects the output of antenna port and
reflected power, U5B buffs and amplify the tested
output signal, then sent to the microcontroller for
processing and display the power and SW value.
3.2.10 Automatic power control circuit
The forward power detection value and the setting
power value are sent into the U22A at the same time
to process automatic power control, and output VALC
voltage to control the amplification of the Q3, so as to
achieve the purpose of automatic power control.

3.3 Control unit / Interface circuit

3.3.1 Microprocessor unit

Microprocessor U17 controls the whole work of
the machine. Its I/O signal is mainly divided into
switching signals and digital signals.
Microprocessor comes with AD/DA converter. The
inside detection signal, such as S table, forward power
and back power, are input to inside the processor to
read by a special ADC port.
The microprocessor expands the I2C memory U8
store the related data information.
3.3.2 External interface circuit unit
X108G has the following external interfaces: AUX,
KEYER, ACC, SPK, Micro-USB.
Micro-USB is the real USB connector and it connects to
the processor U17.
Key interface KEYER is common interface for
manual/automatic key, connects to processor U17.
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