NX-210(G)
12
CIRCUIT DESCRIPTION
1. Overview
The NX-210(G) is a VHF portable transceiver designed
to operate in the frequency range of 136 to 174MHz. The
unit consists of receiver, transmitter, phase-locked loop (PLL)
frequency synthesizer, base band parts, power supply, and
control circuits.
2. Frequency Confi guration
The receiver is a double-conversion superheterodyne us-
ing the fi rst intermediate frequency (IF) of 58.05MHz 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 58.05MHz. This is then mixed with the 57.6MHz
second local oscillator output to produce the 450kHz second
IF. The transmit signal frequency is generated by the PLL
VCO, and modulated by the signal from the DSP. It is then
amplifi ed and fed to the antenna.
x3
57.6MHz
ANT
SW
RF
AMP
MIX
IF AMP
PLL
VCO
Base band circuit
ANT
TX/RX: 136~174MHz
136~174MHz
MCF
CF
450kHz
58.05MHz
19.2MHz
194.05~232.05MHz
PA
AMP
TX
AMP
VC
TCXO
AF
AMP
MIC
AMP
1st MIX
SP
MIC
Fig. 1 Frequency confi guration
Fig. 2 RF and IF circuit
3. Receiver System
3-1. RF Circuit
An incoming RF signal from the antenna terminal is
passed through the antenna switch (D529, D530, D531
and D532) and then the bandpass fi lter (L559, L564). The
bandpass fi lter is adjusted by a variable capacitor. The input
voltage to the variable capacitor is regulated by the voltage
output from the D/A converter (IC801). The signal is ampli-
fied by an RF amplifier (Q522), and passed through the
bandpass fi lter (L546, L553). The resulting signal is applied
to the fi rst mixer (Q517), where it is mixed with the fi rst lo-
cal oscillator signal output from the frequency synthesizer to
produce the fi rst IF (58.05MHz).
3-2. IF Circuit
The fi rst IF signal is passed through a four-pole mono-
lithic crystal fi lter (XF501) to reject adjacent channel signals.
The fi ltered fi rst IF signal is amplifi ed by the fi rst IF amplifi er
(Q515) and then applied to the lF system IC (IC507). The
IF system IC provides a second mixer, AGC amplifi er, and
RSSI (Received Signal Strength Indicator).
The second mixer mixes the first IF signal with the
57.6MHz of second local oscillator output and produces the
second IF signal of 450kHz.
The second IF signal is passed through the ceramic fi lter
(CF501) to reject the adjacent channel signal. The fi ltered
second IF signal is amplifi ed by the AGC amplifi er.
The signal from the AGC amplifi er is input to the ASIC
(IC309) through the ceramic fi lter (CF502) and operational
amplifi er (IC506).
IC103
INAMT
IC809
(2/2)
IC816
SW
SW
IC507
MIX, AGC
EXAMT
IC802
IC805
IC308
ASIC
IC302
DSP
IC814
IC506
IC817
IC801
AMT
VOL
CF502
BPF
IF AMP
Q515
MCF
XF501
BPF
Q506
2nd OSC
X501
19.2MHz
VC
TCXO
x3
CF501
BPF
INT. SP
EXT. SP
RF AMP
Q522
LPF
ANT
ANT
SW
1st MIX
Q517
L562,L563,
L565
BPF
L546,L553
1st PLL OSC (PLL)
BPF
L559,L564
D529,D530
D531,D532