(No.RA032<Rev.001>)1-17
2.4
CIRCUIT DESCRIPTION
2.4.1 Overview
The NX-5900 is a 700/800MHz Analog FM & Digital Mobile transceiver designed to operate in the frequency range of 763 to
775.99375MHz, 793 to 805.99375MHz (700M) and 806 to 825MHz, 851 to 870MHz (800M). The unit consists of a receiver, a trans-
mitter, a phase-locked loop (PLL) frequency synthesizer, a digital control unit, and a power supply circuit.
2.4.2 Frequency Configuration
The receiver is a double-conversion super-heterodyne using first intermediate frequency (IF) of 58.05MHz and second IF of 2.25MHz.
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 55.8MHz second local oscillator output to produce the 2.25MHz 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.
Fig.1 Frequency configuration
2.4.3 Receiver System
2.4.3.1
RF circuit
The receive signal from antenna SW (D305, D306, D308, D310, and D311) is amplified by a RF amplifier (700MHz band: Q501,
800MHz band: Q502) and passes through the band-pass filter (700MHz band: L521, L510, 800MHz band: L522, L511) to remove
unwanted signals. These are controlled with the RF filter switch (IC501 and IC502).The signal is then fed to the 1st mixer (IC500).
2.4.3.2
IF circuit
The first IF signal is passed through a four-pole monolithic crystal filter (XF600) to reject adjacent channel signal. The filtered first IF
signal is amplified by the first IF amplifier (Q604 and Q603) and then applied to the IF system IC (IC600). The IF system IC provides
a second mixer, second PLL, AGC and A/D converter.
The second mixer mixes the first IF signal with the 55.8MHz of second local oscillator output and produces the second IF signal of
2.25MHz.
The second IF signal is then be fed into an ADC, generates the I and Q data. This data is in the form of SSI (Serial Synchronous
Interface), and sent to the DSP (IC706).
2.4.3.3
Audio amplifier circuit
Audio processing (high-pass filter, low-pass filter, de-emphasized and so on) at Analog FM mode and decoding at Digital mode are
processed by DSP. SSI signal from DSP is converted to audio signal at IC902. The signal goes to internal speaker and connector for
external speaker (J900) through the amplifier (IC903), electronic volume control (IC719) and audio amplifier (IC911).
Fig.2 RF and IF circuit
700M:763 775.99375MHz(RX/TX)
793
805.99375MHz(TX)
800M:806 825MHz(TX)
851
870MHz(RX/TX))
700M:763 775.99375MHz(RX/TX)
793
805.99375MHz(TX)
800M:806 825MHz(TX)
851
870MHz(RX/TX)
700M:821 834.04375MHz:
811.95MHz:
800M:792.95
ANT
ANT
SW
PA
AMP
TX
AMP
TCXO
19.2MHz
AMP
RF
1st MIX
58.05MHz
MCF
TX
VCO
PLL
RX
VCO
2nd
VCO
55.8MHz
MIX
IF Circuit
Baseband
Circuit
CODEC
AF
AMP
SP
MIC
ANT
LPF
D305,306
D308,310
D311
SW
ANT
SW
IC501
L521
BPF
L522
BPF
Q501
RF AMP
Q502
RF AMP
L510
BPF
L511
BPF
IC502
SW
IC500
RX VCO/PLL
XF600
BPF
MCF
Q604
IFAMP
IFAMP
Q603
2nd
VCO
Q600
SSI
IF IC
IC600
Internal Speaker
External Speaker
J900
IC911
IC719
VOL
IC903
IC902
CODEC
DSP
IC706
Summary of Contents for NX-5900
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