Table of Contents
Advertisement
NX-220
1. Overview
The NX-220 is a VHF portable transceiver designed to
operate in the frequency range of 136 to 174MHz. The unit
consists of a receiver, transmitter, phase-locked loop (PLL)
frequency synthesizer, 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). The band-
pass fi lter is adjusted by a variable capacitor. The input volt-
age to the variable capacitor is regulated by the voltage out-
ANT
LPF
L114
L115
L116
12
CIRCUIT DESCRIPTION
ANT
TX/RX: 136~174MHz
1st MIX
ANT
RF
SW
AMP
49.95MHz
16.8MHz
185.95~
223.95MHz
PA
TX
AMP
AMP
136~174MHz
Fig. 1 Frequency confi guration
D102,D103
D105,D106
Q202
ANT
BPF
SW
L212
RF AMP
L213
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
put 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 L211). The resulting signal is applied
to the fi rst mixer (Q201), where it is mixed with the fi rst lo-
cal oscillator signal output from the frequency synthesizer to
produce the fi rst IF (49.95MHz).
Q201
1st MIX
XF1
Q303
BPF
BPF
L211
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
Advertisement
Table of Contents
