共查询到20条相似文献,搜索用时 31 毫秒
1.
Calculations of mediumwave skywave field strengths within 100 km of an AM broadcast station using a 186 degree tower are presented. The analysis is novel in that the high vertical elevation angle radiation from the tower is calculated using a method of moments technique. The results show that skywave field strengths are several times stronger than predicted when using the FCC tower radiation formula, and that within 100 km the 10 percent time skywave field strength can in some cases be of comparable amplitude to the groundwave signal amplitude. An analysis of the resulting signal envelope amplitude and phase fading statistics is also presented. 相似文献
2.
硫系玻璃作为优良的消色差和消热差红外材料,是红外光学系统中关键光学元件的理想候选材料,文中利用硫系玻璃实现中波红外光学系统无热化设计。首先分析了温度变化对红外光学系统的影响;其次分析了常用硫系玻璃的各方面特性,并总结了硫系玻璃的优点;最后利用硫系玻璃,镜筒材料选择最常用的铝合金材料,设计了一个工作于中波红外的二次成像全球面无热化成像系统。设计结果表明:在0~100 ℃温度范围内,光学系统的成像质量优异,具有良好的无热化能力。使用硫系玻璃可实现低成本高性能中波红外光学系统。 相似文献
3.
Interference from the daytime skywave signal of one broadcasting station to the groundwave signal of a co-channel station located several hundred kilometers away has been observed in certain parts of the world. The need for a better of skywave propagation at daytime, the Radiocommunications Sector of the International Telecommunications Union (ITU-R, formerly known as the International Radio Consultative Committee, CCIR) adopted Question 215/3 at its 1993 Radio Assembly. This paper is in direct response to this Question. Daytime measurements of more than 30 paths are believed to be skywave and have been studied for detailed information of these paths. The purpose of this paper is twofold: to discuss daytime skywave propagation in a qualitative manner and to present a simple procedure for estimating daytime skywave field strength and interference levels 相似文献
4.
A novel eigen-decomposition technique for estimating the delays of Loran-C skywave components is presented. This provides the basis for a new generation of receivers which implement adaptive skywave interference monitoring, enhancing reliability and positioning accuracy. Performance of the new technique is demonstrated using off-air data 相似文献
5.
6.
High resolution techniques for Loran-C skywave delay estimation 总被引:1,自引:0,他引:1
Two high-resolution estimation techniques are applied to the problem of estimating the delays of the skywave components of signals input to Loran-C receivers. Their performance is evaluated and compared with that of a Fourier-based spectral-division technique. Simulation results show that the high-resolution algorithms improve the accuracy of the estimates significantly and estimate the skywave delay successfully in situations in which the Fourier-based method fails 相似文献
7.
针对增强型罗兰(eLORAN)系统在信号处理中的核心问题——周期识别,该文提出一种应对强天波干扰及低信噪比(SNR)等恶劣环境的联合算法。该方法首先在改进窗函数的基础上利用频谱相除技术估计信号特征参数,并根据大数理论的思想实现了天地波识别;其次,提出天地波时延差及幅度比的自适应2阶网格搜索匹配算法,在节省计算量的同时准确重构并去除天波;最后利用伪地波信号准确实现周期识别。仿真结果分析表明,该算法能够成功地克服现有技术中的一些弊端,实现小时延差及大强度天波干扰下的天波识别及分离,同时结合频谱相除技术的稳定性极大提高周期识别的正确率,进而为后续解调解码等流程提供保障。 相似文献
8.
The ground-loss profile along the path of a skywave for a sectionally homogeneous ground is investigated by means of the compensation theorem. A recurrence procedure, which is suitable for numerical work, has been satisfactorily tested against recent experimental results concerning m.f. skywave propagation over a path in South-East England, extending to 300 wavelengths from the shore. 相似文献
9.
A nonexhaustive chronological summary of the advances made in MF skywave propagation studies is presented with emphasis on progress made in the United States. A qualitative analysis of the documented methods for calculating skywave field strengths and a quantitative comparison of selected methods with measured data are also included. Methods compared include the FCC clear-channel curves (the method for ITU Region 2), the Cairo North-South curve (the official method for the Asian part of Region 3), and the J.C.H. Wang (1985) method (the proposed modified FCC method). Field-strength values calculated by using these methods are compared with data collected in different parts of the world 相似文献
10.
用于罗兰C接收机天波识别的IFFT频谱相除技术探讨 总被引:2,自引:0,他引:2
罗兰C无线电导航接收机所接收的是带有天波干扰的地波信号。为了有效的将天波分离,给出了一种简单但是有效的IFFT的频谱相除技术,应用于罗兰c接收机中采样点的适应性调节,并给出了一种会影响到整体性能的全面、综合的参数分析。仿真结果表明,运算能够在极高噪声环境下成功运行。 相似文献
11.
12.
13.
Details are given of an error monitoring technique applicable to any digital communication system. An example application of the technique to a live skywave HF link using parallel-tone modems is described. The performance of the scheme is presented and discussed for this channel.<> 相似文献
14.
低纬地区天波雷达系统时间可用度研究 总被引:1,自引:0,他引:1
讨论了天波雷达三个与时间有关的“可用度”的区别。强调这种新体制雷达传播媒质电离层是不均匀、各向异位、色散随机介质,雷达传播信道是非线性时变信道,以及天波雷达工作环境的十分复杂性。给出了低纬度地区天波雷达的信道可用度研究方法和实例。研究了给定一定设备能力的天波雷达系统探测不同目标的时间可用度的计算方法和实例,并指出环境噪声对可用度的影响。 相似文献
15.
本文介绍了一种用于弱环境辐射下红外中、短波双波段的红外图像融合方法。该方法先采用单尺度Retinex(SingleScaleRetinex,SSR)方法处理短波图像,分别对处理后的短波图像和中波图像采用均值滤波和双边滤波得到细节层和背景层,再利用基于SpectralResidual(SR)显著性和引导滤波的权重映射,对短波图像和中波图像的细节层和背景层进行加权融合,得到融合图像。经过实验仿真,并与基于小波、拉普拉斯金字塔的多种算法做了比较,该方法在各场景下的主观与客观评价均表现良好。 相似文献
16.
17.
为了减少中小功率中波发射台站建台建设成本,可以采用多频共塔的发射方式,主要介绍了双频共塔天调网络的设计与调试。 相似文献
18.
The performance of a vehicle-mounted loop antenna for near-vertical incidence skywave applications is optimised by using a genetic algorithm in conjunction with the method of moments. Optimum loop current distribution is crucial to performance and this is achieved by appropriate reactive loading 相似文献
19.
20.
论述了天波超视距雷达及多输入多输出体制近年来的发展和研究状况.同时,从分布式天波超视距雷达所面临的任务需求和技术体制等方面展开分析,给出了雷达系统架构以及2种配置方式,并就其资源配置和信息融合进行了设计.最后,根据技术难点和成熟度提出了分布式天波超视距雷达"三步走"的技术发展路线及相应的阶段目标,对其中的关键技术还进行了评述. 相似文献