Kenwood NXR-700H Service Manual page 34

NXR-700H
■ Clock shift circuit
NXR-700H control unit has a crystal oscillation circuit
shown below.
X53-4132-71:
14.7456MHz (IC34 and X1)
16.515072MHz (IC37 and X2)
X53-4140-10:
14.7456MHz (IC325 and X301)
25.8048MHz (IC37 and X2)
25MHz (IC719 and X702)
Each oscillation circuit turns on the NPN transistor
"2SC4738(GR)F" and staggers the oscillating frequency
by approximately –70ppm. This may prevent interference
against transmitter and receiver frequencies. Each transis-
tor is turned on and off by the FPU.
■ Flash ROM (Main MPU)
IC702 is a 128M-bit Flash ROM and contains the firm-
ware of the Main MPU.
■ Flash ROM (Modem control MPU)
IC314 is an 8M-bit Flash ROM and contains the fi rmware
of the Modem control MPU, RX DSP, and TX_Vocoder_DSP.
■ SDRAM
IC704 and IC707 are program execution 128M-bit memo-
ry used by the Main MPU.
■ SRAM
IC700 is a memory backed up by a lithium battery (BA300).
The memory size is 16M-bit. It contains data required for
the system backup.
■ Frame synchronizing signal transmitter and
receiver circuit
J702 and J703 are connectors for synchronizing with
other repeaters in NXDN trunking mode. The differential
rectangular wave that conforms to RS-485, 12.5Hz or 25Hz
is input to and output from this connector for synchronizing
multiple repeaters.
In the repeater system, any given repeater outputs a
synchronizing signal and that synchronous signal is input to
other remaining repeaters.
With regards to the output of the synchronous signal, the
frame signal generated by TX_Vocoder_DSP (IC324) is dif-
ferentially output by IC302.
With regards to the input of the synchronous signal,
IC302 receives a differential signal, and is input to the inter-
ruption of the RX DSP (IC323) and TX_Vocoder_DSP (IC324).
■ 12.288MHz clock PLL circuit
The PLL circuit is installed in the control unit (X53-414) for
operating the RX DSP and TX_Vocoder DSP.
The PLL circuit consists of X300 (12.288MHz VCXO),
IC315 (PLL IC), Q300, Q304, Q305, and IC313.
The purpose of this PLL circuit is to synchronize with the
19.2MHz reference signal controlled by the 10MHz OCXO
(deviation+/-0.4ppm) in the transmitter unit (X56-311).
34
CIRCUIT DESCRIPTION /
电路说明
■时钟位移电路
NXR-700H 控制单元具有如下所示的晶体振荡电路。
X53-4132-71:
14.7456MHz(IC34 和 X1)
16.515072MHz(IC37 和 X2)
X53-4140-10:
14.7456MHz(IC325 和 X301)
25.8048MHz(IC37 和 X2)
25MHz(IC719 和 X702)
各振荡电路开启 NPN 晶体管"2SC4738(GR)F" ，使震荡频率
摆动约 -70p p m。这可以防止对发射机和接收机频率的干扰。
各晶体管由 FPU 开启和关闭。
■ Flash ROM( 主 MPU)
IC702 是一个 128M-bit Flash ROM，含有主 MPU 的固件。
■ Flash ROM( 调制解调器控制 MPU)
I C314 是一个 8M - b i t F l a s h R O M，含有调制解调器控制
MPU、RX DSP 和 TX 声码器 DSP 的固件。
■ SDRAM
IC704 和 IC707 是主 MPU 使用的程序执行 128M-bit 存储器。
■ SRAM
IC700 是由锂电池 (BA300) 支持的存储器。
存储器大小为 16M-bit。它含有系统备份所需的数据。
■帧同步信号发射机和接收机电路
J702 和 J703 是在 N X D N 集群模式下与其它中继台同步的连
接器。符合 R S -485、12.5H z 或 25H z 的差分矩形波被输入到
该连接器并从该连接器输出，使多个中继台同步。
在中继台系统中，指定的任意中继台输出同步信号，同步
信号被输入其余中继台。
对于同步信号的输出，T X 声码器 D S P ( I C324) 生成的帧信
号由 IC302 差分输出。
对于同步信号的输入，I C302 接收差分信号，并输入到 R X
DSP(IC323) 和 TX_ 声码器 DSP(IC324) 的中断。
■ 12.288MHz 时钟 PLL 电路
PLL 电路安装在控制单元 (X53-414) 内，用于操作 RX DSP
和 TX 声码器 DSP。
P L L 电 路 由 X300(12.288M H z V C X O )、I C315( P L L I C )、
Q300、Q304、Q305 和 IC313 组成。
该 P L L 电 路 的 用 途 是 与 发 射 机 单 元 ( X56-311) 内 10M H z
OCXO( 频偏 +/-0.4ppm) 控制的 19.2MHz 基准信号同步。