Kenwood NX-5900 Service Manual page 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.
ANT
700M:763 775.99375MHz(RX/TX)
793
800M:806 825MHz(TX)
851
ANT
SW
PA
AMP
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).
ANT D305,306
D308,310
D311
ANT
LPF
SW
805.99375MHz(TX)
870MHz(RX/TX))
58.05MHz
1st MIX
RF
MCF
AMP
19.2MHz
700M:821 834.04375MHz:
800M:792.95 811.95MHz:
TCXO
PLL
TX TX
AMP VCO
700M:763 775.99375MHz(RX/TX)
793 805.99375MHz(TX)
800M:806 825MHz(TX)
851 870MHz(RX/TX)
Fig.1 Frequency configuration
L521 Q501 L510
IC501
BPF
RF AMP
SW
L522 Q502 L511
BPF
RF AMP
DSP CODEC
IC706 IC902
Fig.2 RF and IF circuit
2nd
VCO
55.8MHz
MIX
IF Circuit
Baseband
Circuit
RX
VCO
IC502
BPF
IC500
XF600
SW
BPF
RX VCO/PLL
VOL
IC903 IC719 IC911
SP
AF
AMP
CODEC
MIC
Q604 Q603
BPF
MCF IFAMP IFAMP
Internal Speaker
External Speaker
J900
(No.RA032<Rev.001>)1-17
2nd Q600
VCO
SSI
IF IC
IC600