Kenwood NEXEDGE NX-720, Service Manual, Page: 20 / 127

NX-720
20
ANT
BPF
Q202
RF AMP
Q305
IF AMP
Q201
1st MIX
XF1
MCF
D107,
D110,D111
ANT
SW
TCXO
IC303
MIX,AGC
1st local
OSC (VCO/PLL)
CF1
LPF
L116,L117 L215,L216
BPF
L207,L209
L210,L220
16.8MHz
Q303
x3
2nd OSC
X1
BPF
CF2
IC 507
ASIC
IC 711
(1/2)
IC 502
DSP
IC 711
(2/2)
VOL
IC 712
IC 714
SP
The second mixer mixes the first IF signal with the
50.4MHz of the second local oscillator output and produces
the second IF signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
(CF1) to reject the adjacent channel signal. The fi ltered sec-
ond IF signal is amplifi ed by the AGC amplifi er.
The signal from the AGC amplifi er is input to the ASIC
(IC507) through the ceramic fi lter (CF2).
CIRCUIT DESCRIPTION /
电路说明
3-3. Audio amplifi er circuit
Audio processing (high-pass filter, low-pass filter, de-
emphasized and so on) in FM mode and decoding in NXDN
mode are processed by the DSP (IC502). Audio signals from
the ASIC (IC507), IC502 goes through the amplifi er (IC711).
The signal then goes through the D/A converter (IC712) and
an amplifi er (IC714).
3-4. Squelch Circuit
It amplifies the demodulated noise signal from ASIC
(IC507) after fi ltering through the LPF and HPF circuit. The
amplifi ed signal is then converted to a DC signal by the de-
tection circuit. The converted signal is fed back to IC507.
ASQAPC
ASQDET
IC507
DET
IC705(1/2)
AMP
RECT
AMP
IC705(2/2)
D702
Q702
ASQ
Fig.2 Receiver System /
图 2 接收机系统
Fig. 3 Squelch Circuit /
图 3 静噪电路
第二混频器混合第一中频信号及 50.4M H z 的第二本地振荡
器输出，生成 450kHz 的第二中频信号。
第二中频信号通过陶瓷滤波器 (CF1) 以消除临近信道的信
号。滤波后的信号由 AGC 放大器进行放大。
A G C 放大器的信号通过陶瓷滤波器 ( C F2) 被输入 A S I C
(IC507)。
3-3. 音频放大器电路
FM 模式的音频处理 ( 高通滤波器、低通滤波器、去加重等 )
和 NXDN 模式的解码由 DSP (IC502) 进行处理。ASIC (IC507)
和 I C502 的音频信号通过放大器 ( IC711)。然后信号通过数
模转换器 (IC712) 和放大器 (IC714)。
3-4. 静噪电路
通过 LPF 和 HPF 电路滤波后，该电路放大 ASIC (IC507)
的已解调噪音信号。随后，放大的信号由检测电路转换为 D C
信号。转换的信号被反馈给 IC507。