XIEGU X108G, Service Manual

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The demodulation of AM mode is accomplished by D2
and its peripheral circuit.
The demodulated SSB, CW and AM audio signals are
input to the U13 audio switcher then switch in
different modes and output.
3.1.7 Audio unit
The audio switcher U13 input an audio signal, this
signal is amplified by the active filter amplifier U7, then
amplified and output by an audio power amplifier U9
(LM386) to drive speaker.
3.1.8 Pulse noise blanking processor NB
Receiving an IF signal which is output by a mixer enters
the NB amplification/control unit after Q22 buffering,
this part is composed of U3, Q27, D47, Q29, Q34, Q30,
Q28 and Q6. When the pulse interference signal
strength exceeds the threshold, this circuit starts to
work, Q6 controls the IF preamplifier Q21 to be shutoff
to bring the noise elimination.
3.2 Transmitting circuit
3.2.1 Microphone amplifying circuit
The microphone amplifying circuit is located on the
power board, and consists of U15B and U17B. U15B
(SSM2167) has voice amplification and voice
compression function, and the compression ratio is
switched by U15B.
3.2.2 Modulator circuit
The microphone amplified signal enters the modulator
U6 via the audio switch U27 to do SSB modulation. AM
modulator circuit consists of U6, Q10, D3, D8 and so on,
to restore carrier and modulate.
3.2.3 Transmit 1 IF amplified / filtered circuit
The output signal of the debugger U6 is amplified by
Q25 and then enters the IFCF (XMD1, XMD2, XF1) for
filtering, then amplified by Q3 for the second time, and
output to the transmitting mixer by T8.
The CW_TXE signal is the transmit control enable signal
in the CW mode.
3.2.4 Transmitted mixer
T8 outputs a transmitting 1 IF signal which is sent to
the transmit mixer U10 (AD831) for mixing, then
output a final transmitting small signal by the 16 pin.
3.2.5 Transmit small signal filter/output switching
U10 outputs a small signal and this small signal is
filtered through the BPF module (XGM1 - XGM5), and
then output transmitting final small signal by a electric
switcher which is composed of D28 and D9, the
interface is P2 (U.FL socket).
R99
2.7k
R89
2.7k
C82
100nF
C106
100nF
L30
100uH
L37
100uH
C87
100nF
C100
100nF
+9R
+9T
P1
U.FL 插座
P2
U.FL 插座
D27
MA2Z077
D28
MA2Z077
C73
100nF
L22
100uH
R131
2.7k
D9
MA2Z077
1
TP15
NC
1
TP16
NC
AF_AM
R142
1k
R14
1k
1 2
3
D2
1SS372
R144
100k
C28
4.7nF
R143
68k
+9
R5
15k
C17
470nF
C165
2.2nF