Kenwood NX-3720HG Service Manual page 16

2.4 CIRCUIT DESCRIPTION
2.4.1 Overview
The NX-3720H/3720 is a VHF Analog FM & Digital Mobile transceiver designed to operate in the frequency range of 136 to 174MHz.
The NX-3820H/3820 is a UHF Analog FM & Digital Mobile transceiver designed to operate in the frequency range of 450 to 520MHz
(K) or 400 to 470MHz (K2, E).
The unit consists of a transceiver IC, a transmitter, a digital control unit, and a power supply circuit.
2.4.2 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 DSP. It is then amplified and fed to the antenna.
ANT
SW
FINAL DRIVE
AMP AMP
2.4.3 Receiver System
2.4.3.1 RF circuit
The receive signal from ANT SW (D205, D206, D207, D208 and D209) passes through the high-pass filter (L303, L304, L313, L315
and L317 (L315 and L317 are the NX-3720H/3720 only.)) to remove unwanted signals and amplified by a RF amplifier (incorporated
in IC302) . The signal is then fed to the mixer (incorporated in IC302) and converted to the baseband signal.
2.4.3.2 Baseband circuit
The baseband signal is then be fed into an ADC (incorporated in IC302), generates the I and Q data. This data is in the form of Serial
Interface, and sent to the MPU/DSP (IC404).
ANT
D205, D206
D207, D208
D209
ANT ANT
LPF SW
2.4.3.3 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. I2S signal from DSP is converted to audio signal at IC607. The signal goes to internal speaker and connector
for external speaker (J2) through the electronic volume control (IC412), pre amplifier (IC608) and audio power amplifier (IC601).
1-16 (No.RA054<Rev.001>)
VCO
TRANSCEIVER
IC
TCXO
19.2MHz
Fig.1 Frequency Configuration
L303,L304
L313,L315
L317
HPF
IC302
RFAMP
Fig.2 RF and Baseband circuit
BASEBAND
CIRCUIT
L308, L309
L310, L311
HPF
MIXER
PLL
VCO
AF
AMP
CODEC
MIC
IC404
Serial
I/F
ADC MPU/DSP
SP