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NXR-700H
Unit X53-414 has the mode selection (analog or NXDN)
circuit, NXDN mode communication processing circuit, LAN
interface circuit, and Compact Flash interface circuit.
6-1. X53-413
■ RF control MPU
The IC34 RF control MPU is a 16-bit single chip micropro-
cessor incorporating 256K bytes of ROM and 20K bytes of
RAM.
This MPU controls the Flash ROM, DSP, receiver unit,
transmitter unit, and EEPROM of each unit, and the display
circuit, and has communication I/F with external devices.
■ DSP
The DSP circuit is in charge of the fi ltering of transmitting
and receiving signals, and the encoding and decoding of
sub-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 to
digital by IC4 with a sampling frequency of 16.128kHz. The
digitized audio signal is sent to the DSP (IC37) to process
the sub-audible signal and audio signal. The processed digi-
tal audio signal is applied to CODEC IC4, and is converted
from digital to analog. The analog signal is output from
pin16 (AOUTR). The audio signal is then amplifi ed by IC12
(A/2), passes through the low-pass fi lter at IC12 (B/2), is se-
lected by the multiplexer IC14 (Y0=Y) and is then input into
an electronic volume IC8.
On the other hand, the transmitting audio signal output
from IC3 is amplifi ed by IC9 (A/4), applied to pin 3 (AINL)
of CODEC IC4, and is then converted from analog to digital
at a sampling frequency of 16.128kHz. The digitized trans-
mitting audio signal is AGC-processed, pre-emphasized
and fi ltered, except for the 300Hz to 3kHz range, by DSP
IC37, and is then feed back to CODEC IC4, converted from
digital to analog, and the analog signal is output from pin15
(AOUTL). The transmitting signal from the AOUTL is am-
plifi ed by IC9 (B/4), passed through the IC9 (C/4) low-pass
fi lter, and sent to the IC9 (D/4) summing amplifi er.
IC31 is a counter IC. The clock required for the CODEC
and DSP is generated by dividing the 16.515072MHz clock
signal supplied by the DSP IC37.
RX detected signal / RX 检测信号
TX modulation signal / TX 调制信号
Fig. 24 An audio signal course and the frequency characteristic / 图 24 音频信号路径和频率特性
30
CIRCUIT DESCRIPTION /
(AINR)
RD
Local Mic / 本地麦克风
(AINL)
TA
[Frequency response]
[ 频率响应 ]
REPEAT
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 MPU
IC34 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。
■ DSP
D 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。
CODEC IC
IC4: AK4550VTP
2
16
RX
(AOUTR)
REPEAT
3
15
TX
(AOUTL)
TD
300Hz
3kHz
RX
(De-emphasis)
( 去加重 )
TX
(Pre-emphasis)
( 预加重 )
(300Hz~3kHz Flat)
RA
RX audio amp.
RX 音频放大器
TX VCO
(Modulation circuit)
( 调制电路 )
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