Kenwood NXR-700H Service Manual

NXR-700H30Unit X53-414 has the mode selection (analog or NXDN)circuit, NXDN mode communication processing circuit, LANinterface circuit, and Compact Flash interface circuit.6-1. X53-413■ RF control MPUThe IC34 RF control MPU is a 16-bit single chip micropro-cessor incorporating 256K bytes of ROM and 20K bytes ofRAM.This MPU controls the Flash ROM, DSP, receiver unit,transmitter unit, and EEPROM of each unit, and the displaycircuit, and has communication I/F with external devices.■ DSPThe DSP circuit is in charge of the filtering of transmittingand receiving signals, and the encoding and decoding ofsub-audible signals (encode: QT, DQT, DTMF, decode: QT,DQT, DTMF).This circuit consists of IC37, IC30, IC31, IC4, IC5, IC9,and IC12.The receiving signal, DET is converted from analog todigital by IC4 with a sampling frequency of 16.128kHz. Thedigitized audio signal is sent to the DSP (IC37) to processthe sub-audible signal and audio signal. The processed digi-tal audio signal is applied to CODEC IC4, and is convertedfrom digital to analog. The analog signal is output frompin16 (AOUTR). The audio signal is then amplified by IC12(A/2), passes through the low-pass filter at IC12 (B/2), is se-lected by the multiplexer IC14 (Y0=Y) and is then input intoan electronic volume IC8.On the other hand, the transmitting audio signal outputfrom IC3 is amplified by IC9 (A/4), applied to pin 3 (AINL)of CODEC IC4, and is then converted from analog to digitalat a sampling frequency of 16.128kHz. The digitized trans-mitting audio signal is AGC-processed, pre-emphasizedand filtered, except for the 300Hz to 3kHz range, by DSPIC37, and is then feed back to CODEC IC4, converted fromdigital to analog, and the analog signal is output from pin15(AOUTL). The transmitting signal from the AOUTL is am-plified by IC9 (B/4), passed through the IC9 (C/4) low-passfilter, and sent to the IC9 (D/4) summing amplifier.IC31 is a counter IC. The clock required for the CODECand DSP is generated by dividing the 16.515072MHz clocksignal supplied by the DSP IC37. CODEC ICIC4: AK4550VTPRX detected signal / RX 检测信号 (AINR) (AOUTR)(AOUTL)(AINL)RDTATX modulation signal / TX 调制信号Local Mic / 本地麦克风23REPEATRXTX1615TDRARX audio amp.RX 音频放大器TX VCO(Modulation circuit)( 调制电路 )300Hz 3kHz[Frequency response][ 频率响应 ]RXTXREPEAT(De-emphasis)( 去加重 )(Pre-emphasis)( 预加重 )(300Hz~3kHz Flat)Fig. 24 An audio signal course and the frequency characteristic / 图 24 音频信号路径和频率特性CIRCUIT DESCRIPTION / 电路说明单元 X53-414 包括模式选择 ( 模拟或 NXDN) 电路、NXDN 模式通信处理电路、LAN 接口电路以及 Compact Flash 接口电路。6-1. X53-413■ RF 控制 MPUIC34 RF 控制 MPU 是一个 16 位单片微处理器，结合了 256K字节的 ROM 和 20K 字节的 RAM。该 MPU 控制 Flash ROM、DSP、接收机单元、发射机单元、各单元的 EEPROM 以及显示电路，并有与外部设备的通信 I/F。■ DSPD S P 电路负责发射和接收信号的过滤，以及亚音信号的编码和解码 ( 编码 : QT、DQT、DTMF，解码 : QT、DQT、DTMF)。该电路由 IC37、IC30、IC31、IC4、IC5、IC9 和 IC12 组成。接收信号、D E T 由 I C4 以 16.128k H z 的取样频率从模拟信号转换为数字信号。数字化的音频信号被发送到 D S P ( I C37)，对亚音信号和音频信号进行处理。经过处理的数字音频信号施加于 C O D E C I C4，从数字转换为模拟。模拟信号从针脚16( A O U T R ) 输出。然后，音频信号由 I C12( A /2) 放大，通过IC12 (B/2) 的低通滤波器，由多路器 IC14(Y0=Y) 进行选择，然后被输入到电子音量 IC8。另一方面，从 I C3 输出的发射音频信号由 I C9( A /4) 放大，施加于 CODEC IC4 的针脚 3(AINL)，然后从模拟信号转换为取样频率为 16.128kHz 的数字信号。除 300Hz 到 3kHz 的范围外，数字化的发射音频信号由 DSP IC37 进行 AGC 处理、预加重和过滤，然后反馈到 CODEC IC4，从数字转换到模拟，模拟信号从针脚 15(AOUTL) 输出。AOUTL 的发射信号由 IC9(B/4) 放大，通过 IC9(C/4) 低通滤波器，然后发送到 IC9(D/4) 加法放大器。I C31 是一个计数器 I C。通过分割 D S P I C37 提供的16.515072MHz 时钟信号，生成 CODEC 和 DSP 所需的时钟。