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NX-800/800H
18
3-3. IF circuit
The fi rst IF signal is passed through a four-pole mono-
lithic crystal fi lter (XF202) to reject adjacent channel signal.
The fi ltered fi rst IF signal is amplifi ed by the fi rst IF amplifi er
(Q204, Q205) and then applied to the lF system IC (IC202).
The IF system IC provides a second mixer, AGC amplifi er,
and RSSI (Received Signal Strength Indicator).
The second mixer mixes the first IF signal with the
57.6MHz of second local oscillator output and produces the
second IF signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
(CF201, CF202) to reject the adjacent channel signal. The
fi ltered second IF signal is amplifi ed by AGC amplifi er.
The signal from AGC amplifi er is input to AD converter
(IC510) through ceramic fi lter (CF203) and operational ampli-
fi er (IC201 and IC704).
CIRCUIT DESCRIPTION
IC715Q710
AF AMP
INAMT
IC711
(2/2)
MUTE
SW
Q709IC502
SW
SW
IC202
MIX. AGC
IC701 IC707IC704
IC510
DSP
IC201
IC712
AMT
VOL
RF Circuit (Front end)
CF203
BPF
Q203
2nd OSC
X1
19.2MHz
VC
TCXO
x3
CF201
CF202
BPF
INT. SP
EXT. SP
ANT
Fig. 3
Fig. 4
3-4. Audio amplifi er circuit
Audio processing (high-pass filter, low-pass filter, de-
emphasized and so on) at FM mode and decoding at NXDN
mode are processed by DSP. Audio signal from IC510,
IC502 goes through the amplifi er (IC701). The signal then
goes through mute switch (IC707), amplifier (IC711), and
electronic volume control (IC712).
While busy, INAMT becomes High, turn switch (Q709)
on and Mute switch (Q710) off, and signal is fed to AF Pow-
er Amp (IC715). While Non-busy, INAMT is become Low,
turn switch (Q709) off and Mute switch (Q710) on, then
there is not AF output.
3-5. Squelch Circuit
It amplifies the demodulated noise signal from IC202
after fi ltering through BPF circuit. Then, the amplifi ed signal
is converted to DC signal by the detection circuit. The con-
verted signal is fed back to IC510.
IC202 IC510
IC705 (2/2)
FMDET
ASQDET
VAGC
RSSI
BPF
Q702
AMP
D703
RECT
IC705 (1/2)
AMP
IC203 (1/2)
AMP
IC203 (2/2)
AMP