NX-800
18
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 first mixer.
1. Overview
NX-800 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 syn-
thesizer, base band parts, power supply, and control circuits.
2. Frequency Configuration
The receiver is a double-conversion super heterodyne
using first intermediate frequency (IF) of 58.05MHz and sec-
ond IF of 450kHz. Incoming signals from the antenna are
mixed with the local signal from the PLL circuit to produce
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
generated by the PLL VCO, and modulated by the signal from
the DSP. It is then amplified and fed to the antenna.
CIRCUIT DESCRIPTION

Fig. 1 Frequency configuration

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

3-2. First Mixer

The signal from the BPF is heterodyned with the first local
oscillator signal from the PLL frequency synthesizer circuit at
the first mixer DBM (IC204) to become a 58.05MHz first
intermediate frequency(IF) signal.
The first IF signal is fed through a monolithic crystal
filter(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

Fig. 2