NX-200
31
CIRCUIT DESCRIPTION /
电路说明
1. Overview
The NX-200 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
using the first 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 gener-
ated 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 /
图 1 频率构成
1. 概述
NX-200 为 VHF 便携式手持对讲机，设计用于 136 至 174MHz
的频率范围。该设备由接收机，发射机，锁相环 ( P L L ) 频率
合成器，基带部分，电源和控制电路组成。
2. 频率构成
接收机为二次变频超外差方式，使用的第一中频 ( I F ) 为
58.05MHz，第二中频为 450kHz。天线接收到的信号与 PLL 电
路的本振信号混频，从而产生第一个 58.05M H z 的中频。然后
与第二个 57.6M H z 的本地振荡器输出信号混频，进而产生第
二个 450kHz 的中频。发射的信号频率由 PLL VCO 生成，并经
DSP 信号调制。最后，该信号频率经过放大并发送到天线。
