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NXR-901
4-3. 1st-IF circuit
The IF1 signal produced by the 1st-Mixer circuit is
passed to 1st IF circuit.
The 1st IF circuit consists of XF1, Q204.
This signal path is used for analog narrow FM, narrow
digital, very narrow digital and mixed operation mode.
14
CIRCUIT DESCRIPTION
L203
Q201
L210
CN5
IC201
R210
5V
Fig. 14 Front-end circuit
IC205
RF
1st
coupler
mixer
Fig. 15 1st-Mixer circuit
IC202
Electric
ATT
IC205
XF1
1st
mixer
Fig. 16 1st-IF circuit
RF AGC
control
Electric
RF
ATT
coupler
IC202
CN68
IC811
#15
XF1
Q11
Q10
Freq.
doubler
XF1 is 4-pole Monolithic Crystal Filters (MCF). This is a
BPF for removing spurious noise occurring close to the de-
sired signal.
The fi nal 1st IF amplifi er is Q211 to have enough total
gain from the RX antenna to the IF system IC.
The fi ltered 1st IF signal is coupled to the Q202 IF ampli-
fi er to construct the RF AGC loop. The loop works to protect
the MCF from a very large antenna input signal (i.e. -10 to
10dBm).
IC805
#3
IC204
IC204
B/2
A/2
D203
Q202
Q204
3dB
divider
Q211
XF1
1st
mixer
IC205
1st Lo
PLL block
3dB
divider
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