Circuit Description; Frequency Confi Guration; Receiver System; Rf Circuit - Kenwood NX-320 Series Service Manual

NX-320
1. Overview
The NX-320 is a UHF portable transceiver designed to
operate in the frequency range of 450 to 520MHz (K,K2,K3)
or 400 to 470MHz (K4,K5,K6,E,E2,E3). The unit consists of a
receiver, transmitter, phase-locked loop (PLL) frequency syn-
thesizer, baseband parts, power supply, and control circuits.

3. Receiver System

3-1. RF circuit

An incoming RF signal from the antenna terminal is
passed through the antenna switch (D102, D103, D105 and
D106) and then the band-pass fi lter (L212, L213 and L214).
The band-pass fi lter is adjusted by a variable capacitor. The
input voltage to the variable capacitor is regulated by the
ANT
LPF
L114
L115
L116
12

CIRCUIT DESCRIPTION

ANT
TX/RX:
1st MIX
ANT RF
SW AMP
49.95MHz
16.8MHz
PA TX
AMP AMP
400~470MHz (K4,K5,K6,E,E2,E3)
450~520MHz (K,K2,K3)
Fig. 1 Frequency confi guration
D102,D103
D105,D106 Q202
ANT
BPF
SW
L212 RF AMP
L213
L214
Fig. 2 RF and IF circuit
2. Frequency Confi guration
The receiver is a double-conversion superheterodyne
using the first intermediate frequency (IF) of 49.95MHz
and the second IF of 450kHz. Incoming signals from the
antenna are mixed with the local signal from the PLL circuit
to produce the fi rst IF of 49.95MHz. This is then mixed with
the 50.4MHz 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.
CF
450kHz
MCF
MIX
IF AMP
x3
TCXO
50.4MHz
PLL
VCO
350.05~420.05MHz (K4,K5,K6,E,E2,E3)
400.05~470.05MHz (K,K2,K3)
voltage output from the D/A converter (IC4). The signal is
amplifi ed by an RF amplifi er (Q202), and passed through the
band-pass fi lter (L207, L208 and L209). The resulting signal
is applied to the fi rst mixer (Q201), where it is mixed with
the first local oscillator signal output from the frequency
synthesizer to produce the fi rst IF (49.95MHz).
Q201
1st MIX XF1 Q303
BPF BPF
L209 MCF IF AMP
L208
1st PLL
X401 Q301
L207
OSC (PLL)
TCXO x3
16.8MHz
IC610 IC904
ASIC
DSP
IC603
SP
AF
AMP
MIC
MIC
AMP
IC302
MIX, AGC
BPF
CF1
2nd OSC
IC2 (1/2) IC4 IC901
VOL
CF2
BPF
SP