载波快速捕获与跟踪的双数字锁频环路无缝切换

锁频环广泛应用于载波频率快速同步的场合,为解决大捕获范围和跟踪精度之间的矛盾,通常捕获和跟踪状态时采用带宽不同的频率锁定环路,并根据载波同步情况进行切换.对这种硬切换所导致的跟踪环路的收敛过程、瞬态时间进行分析,并基于二阶锁频环与卡尔曼滤波等效结构,应用卡尔曼滤波算法进行两种状态之间环路增益时变的无缝切换.推导出高动态数字直扩接收机差积鉴频二阶锁频环路无缝切换控制增益,两种切换方式的仿真结果表明无缝切换的效果优于传统的硬切换方式.     

基于NIOSII的多模导航接收机跟踪环路

硬件实现卫星导航接收机时,信号跟踪、数据解调、原始观测量提取、定位解算功能通常由DSP或ARM实现,捕获及通道由FPGA实现。多模卫星导航接收机是未来发展趋势,其通道数目多。为降低外部处理器计算负荷,将数据解调、环路跟踪、原始观测量提取功能由NIOSII实现。跟踪环路不使用float型计算可节约硬件资源。据跟踪环路原理,采用递推方法进行分析,以32位整型计算进行实现。测试表明计算误差小,计算速度高,节约了FPGA资源。     

Fiber optic displacement sensor used in railway turnout contact monitoring system

Railway turnout contact monitoring is very important in high-speed rail operation systems. In order to measure the distance between the sharp rail and the basic rail in a switch system, a wide-range, high-precision fiber Bragg grating (FBG) displacement sensor was designed. Because the distance between the sharp and basic rails is always greater than 14 cm, the measurement range width and accuracy of the proposed sensor system are ensured through the use of a long spring and a beam of constant strength. A differential compensation method is used to eliminate temperature effects. Test results show that the resolution of the proposed sensor is 0.040 mm and the measuring range is 0—170 mm. A field test was also carried out to evaluate the performance of the sensors.     

共缆传输使村屯广播又响起来

1997年7月,辽宁省北宁市王粮乡广播站的广播节目,一不经过调频广播发射机发射,二不用广播专线传输,却神奇地从安装了有线电视农户收音机里传了出来,就连村头的高音喇叭里也传出了乡站自办广播节目的声音。这片希望田野上久违多时的广播声又重新响了起来。前几年,在农村广播大幅度滑坡的情况下,王粮乡从乡到村的广播专用地埋线因日久年深,多处中断,乡广播站的自办节目很难送到各个村屯。为改变这种状况,王粮乡广播站的工作人员在党委、政府的