FP520 Service Manual
Page 7 of 64
Receiver Front End
Signals from the antenna through the receiving/transmission (RX/TX) switch (D600
,
D601
,
D602
,
D603), which
passed the band-pass filter (BPF) consisting of two levels of LC to eliminate the unnecessary signals, then sent to
the low noise amplifier (LNA) consisting of Q703 and its peripheral components for enlargement.
After passing the band-pass filter (BPF) consisting of three levels of LC to further eliminate the unnecessary
out-of-band signals, the output of LNA is then sent to the first frequency mixer (Q702).
The First Frequency Mixer
The signal from LNA is mixed with the first local oscillator signal from the frequency synthesizer to generate the first
intermediate-frequency signal (51.65MHz).
IF Circuit
The first intermediate-frequency signal eliminates the signals from the adjacent channels or other signals through
the crystal filter. (Z1)
The first intermediate-frequency signal from the crystal filter, being amplified by the first intermediate-frequency (IF)
amplifier (Q701), then sent to IF processing IC ( IC700
,
GT3136).
IF IC consists of the second frequency mixer, IF amplifier, amplitude limiter, frequency detector, noise amplifier,
audio low pass filter.
The 12.8MHz signal from X300, being amplified by Q300 and its peripheral circuit, becomes the second local
oscillation signal (51.2MHz). The second local oscillation signal (51.2MHz) mixes with the first
intermediate-frequency signal (51.65MHz) in IC700 to generate the second intermediate-frequency signal. The
second intermediate-frequency signal amplified in IC700 with its amplitude being limited, being filtered by the FD1
ceramic filter
(
450kHz
)
, is demodulated by IC700 to generate the audio signal.
Squelch Circuit
The signal demodulated by IC700 is sent to its own noise amplifier for amplification, and the amplified signal is sent
to Q700 for further amplification and to D701 for detection; the produced direct current is then sent to MCU squelch
control circuit, and its voltage is inversely proportional to the input signal.
3.4 Principle of Transmitter (TX)
BT
SW
D402
AMP
Q602,Q603
DRIVE AMP
Q601
FINAL AMP
Q600
ANT SW
D600,D601
LPF
D602
RX
VCO
APC
IC600
DET
SW
Q604,Q605
APC
R620,R621,R622
ANT
5T
5T
Summary of Contents for FP520
Page 1: ... 键入文档副标题 gh 选取日期 在此处键入文档的摘要 摘要通常是对文档内容的简短总结 在此处键入文档的摘要 摘要 通常是对文档内容的简短总结 ...
Page 44: ...FP520 Service Manual Page 43 of 64 Figure 1 FP520 01 Mainboard Schematic Diagram 136 174MHz ...
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Page 54: ...FP520 Service Manual Page 53 of 64 Figure 4 FP520 02 Mainboard Schematic Diagram 400 470MHz ...
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Page 64: ...FP520 Service Manual Page 63 of 64 Figure 7 KBC 51 7 4V Electrical Schematic Diagram ...