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NX-800/800H
17
CIRCUIT DESCRIPTION
1. Overview
NX-800/800H is a UHF Mobile transceiver designed to
operate in the frequency range of 450 to 520MHz. The unit
consists of receiver, transmitter, phase-locked loop (PLL)
frequency synthesizer, base band parts, power supply, and
control circuits.
2. Frequency Confi guration
The receiver is a double-conversion super heterodyne
using first intermediate frequency (IF) of 58.05MHz and
second IF of 450kHz. Incoming signals from the antenna
are mixed with the local signal from the PLL circuit to pro-
duce the first IF of 58.05MHz. This is then mixed with
the 57.6MHz second local oscillator output to produce the
450kHz second IF. The transmit signal frequency is gener-
ated by the PLL VCO, and modulated by the signal from the
DSP. It is then amplifi ed and fed to the antenna.
x3
57.6MHz
ANT
SW
RF
AMP
MIX
IF AMP
PLL
VCO
Base band Circuit
ANT
TX/RX: 450~520MHz
MCF
CF
450kHz
58.05MHz
19.2MHz
450~520MHz
391.95~
461.95MHz
PA
AMP
TX
AMP
VCTCXO
AF
AMP
MIC
AMP
1st MIX
SP
MIC
Fig. 1 Frequency confi guration
Fig. 2
3. Receiver System
3-1. RF circuit
The front-end circuit consists of former BPF (D212,
D213), RF amplifier Q210, and latter BPF (D207, D208,
D209 and D210).
The BPF covers frequency ranges 450 to 520MHz.
The latter BPF (D207, D208, D209 and D210) attenuates
the unwanted signals, and sends only the necessary signal
to the fi rst mixer.
3-2. First Mixer
The signal from the BPF is heterodyned with the fi rst lo-
cal oscillator signal from the PLL frequency synthesizer cir-
cuit at the fi rst mixer DBM (IC204) to become a 58.05MHz
fi rst intermediate frequency (IF) signal.
The fi rst IF signal is fed through a monolithic crystal fi lter
(XF202) to further remove spurious signals.
RF AMP
Q210
Buff AMP
Q208
BPF
ANT
IF AMP
Q205
IF AMP
Q204
RX
VCO
Buff AMP
Q10
Buff AMP
Q9
BPF
1st MIX DBM
IC204
D212,D213
BPF
D207~
D210
MCF
XF202
FM SYSTEM IC
IC202
–118dBm
–120.5dBm –104dBm–114.5dBm –112.5dBm
0dBm0dBm