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NX-900
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
(Q205,Q204) and is then applied to the IF 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 the 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 l-
tered second IF signal is amplifi ed by the AGC amplifi er.
The signal from the AGC amplifier is input to the A/D
converter (IC510) through the ceramic fi lter (CF203) and op-
erational amplifi er (IC201 and IC704).
CIRCUIT DESCRIPTION
IC715
Q710
AF AMP
/INAMT
IC711
(2/2)
MUTE
SW
Q709
IC717
SW
SW
IC202
MIX, AGC
IC701
IC707
IC704
IC510
DSP
IC201
IC719
AMT
VOL
RF/1st IF Circuit
CF203
BPF
Q203
2nd OSC
X1
19.2MHz
VC
TCXO
x3
Q11
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, etc.) at FM mode and decoding at NXDN mode
are processed by the DSP (IC717). The audio signal from
IC510, IC717 goes through the amplifi er (IC701). The signal
then goes through the mute switch (IC707), amplifi er (IC711),
and electronic volume control (IC719).
While busy, INAMT becomes High, turning the switch
(Q709) on and the Mute switch (Q710) off, and the signal is
fed to the AF Power Amp (IC715). While not busy, INAMT
becomes Low, turning the switch (Q709) off and the Mute
switch (Q710) on (there is no AF output).
3-5. Squelch Circuit
The squelch circuit amplifies the demodulated noise
signal from IC202 after fi ltering through the BPF circuit. The
amplifi ed signal is then converted to a DC signal by the de-
tection circuit. The converted signal is fed back to IC510.
IC202
IC510
IC705 (2/2)
FM_DET
ASQDET
VAGC
RSSI
BPF
Q702
AMP
D703
RECT
IC705 (1/2)
AMP
IC203 (1/2)
AMP
IC203 (2/2)
AMP
Summary of Contents for NEXEDGE NX-900
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