1-8 (No.RA077<Rev.001>)
2.3
CIRCUIT DESCRIPTION
2.3.1 Overview
The NX-1200 series is a VHF Analog FM & Digital Portable transceiver designed to operate in the frequency range of 136 to 174MHz.
The unit consists of a transceiver IC, a transmitter, a digital control unit, and a power supply circuit.
The NX-1300 series is a UHF Analog FM & Digital Portable transceiver designed to operate in the frequency range of 400 to 470MHz.
The unit consists of a transceiver IC, a transmitter, a digital control unit, and a power supply circuit.
2.3.2 Frequency Configuration
The receiver uses the direct conversion system. Incoming signals from the antenna are mixed with the local signal from the PLL circuit
and converted to the baseband signal. The transmit signal frequency is generated by the VCO/PLL, and modulated by the signal from
the MPU/DSP. It is then amplified and fed to the antenna.
Fig.1 Frequency configuration
2.3.3 Receiver System
2.3.3.1
RF Circuit
The receive signal from the antenna switch (D101, D102, D103 and D104) passes through the band-pass filter (D200 and D201) to
remove unwanted signals and amplified by a RF amplifier (Q200). The signal passes through another band-pass filter (D202 and
D203) to remove unwanted signals. Then the signal is amplified again by a RF amplifier (incorporated in Transceiver IC (IC200)) and
fed to the mixer (incorporated in Transceiver IC) and converted to the baseband signal.
2.3.3.2
Baseband Circuit
The baseband signal (I/Q signal) pass through amplifiers IC201 & IC202 and is then sent to the MPU/DSP (IC501).
Fig.2 Receiver System
2.3.3.3
Audio Amplifier Circuit
Audio processing (high-pass filter, low-pass filter, de-emphasized and so on) at Analog FM mode and decoding at Digital mode are
processed by MPU/DSP. The Digital signal from MPU/DSP is converted to audio signal at D/A converter (IC604).
The signal goes to internal speaker through the Class-D amplifier (IC302) or Jack connector for external speaker through the single-
end audio power amplifier (IC300).
Fig.3 Audio amplifier circuit
ANT SW
RF AMP
ANT
FINAL AMP
DRIVE AMP
TRANSCEIVER IC
VCO
PLL
TCXO
MPU/DSP
AF AMP
MIC AMP
SP
MIC
ANT
ANT SW
RF AMP
HPF
VCO
OP AMP
(I/Q)
MPU/DSP
IC200
BPF
BPF
MIXER
IC501
D101
D102
D103
D104
D200
D201
Q200
D202
D203
TRANSCEIVER IC
IC201
IC202
RF AMP
Q4
TRANSCEIVER IC
MPU/DSP
D/A Converter
AUDIO AMP
OP AMP
(I/Q)
IC200
IC201
IC202
IC501
IC604
IC302
IC300
Internal Speaker
External Speaker
AUDIO AMP
