Circuit Description; Overview; Frequency Configuration; Receiver System - Kenwood NX-5400 Service Manual

(6) Attach two spacers to the back side of the orange rubber
seal as indicated below.
Note:
Rubber seal may not attach correctly if the spacer is
brought near by the corner too much.
(7) Reinstall the cover and orange rubber seal using the 4
screws removed in step 2 and 3.
Note:
When installing the rubber orange seal on the chassis,
ensure that you do not damage the rubber seal and that
the contact area of the chassis is dust-free.
2.4

CIRCUIT DESCRIPTION

2.4.1 Overview

The NX-5400 is a 700/800MHz FM & P25 Portable 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 transmitter, a phase-locked loop (PLL) frequency synthesizer, a digital control unit, and a power sup-
ply circuit.

2.4.2 Frequency Configuration

The receiver is a double-conversion super-heterodyne using a 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.
700M:763~775.99375MHz(RX/TX)
ANT
793~805.99375MHz(TX)
800M:806~825MHz(TX)
851~870MHz(RX/TX)
ANT RF
SW AMP
19.2MHz
TCXO
PA TX
AMP
AMP
700M:763~775.99375MHz(RX/TX)
793~805.99375MHz(TX)
800M:806~825MHz(TX)
851~870MHz(RX/TX)

2.4.3 Receiver System

2.4.3.1 RF Circuit
The receive signal from antenna switch (D350, D370 and D371) is amplified by a RF amplifier (700MHz band: Q530, 800MHz band:
Q550) and passes through the band-pass filter (700MHz band: L536, L530, 800MHz band: L556, L550) to remove unwanted signals.
These are controlled with the RF filter switch (IC570 and IC520). 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 (XF670) to reject adjacent channel signals. The filtered first IF
signal is amplified by the first IF amplifier (Q670 and Q660) 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 A/D converter, generates the I and Q data. This data is in the form of SSI (Serial Synchro-
nous Interface), and sent to the DSP (IC702).
Spacer
1st MIX 58.05MHz
MCF
700M:821.05~834.04375MHz
800M:792.95~811.95MHz
TX PLL
VCO
Fig.1 Frequency configuration
Note:
• When the KWD-AE30/ KWD-AE31 is installed, select the
"Secure Cryptographic Module" checkbox in the Product In-
formation of the KPG-D1/KPG-D1N (programming soft-
ware), and then set each parameter.
• If the KWD-AE30/ KWD-AE31 connector is not properly in-
stalled, the TX/RX indicator will blink red or "No SCM" will
appear on the display when the transceiver power is turned
on.
• If the Encryption Key data is not written at the Keyloader, or
the Encryption Key data is zeroized, "Key Fail" will appear
on the display.
• If the KWD-AE30/ KWD-AE31 is installed in other transceiv-
ers, the Encryption Key data will be forced to zeroize.
2nd
VCO
55.8MHz
MIX
IF Circuit
Baseband
Circuit
RX PLL
VCO
SP
AF
AMP
CODEC
MIC
(No.RA016<Rev.001>)1-11