星载的VLF发射环天线在海面上产生的场

用于对潜通讯的星载的ＥＬＦ／ＶＬＦ发射环天线处于３５０ｋｍ高度的电离层Ｆ２层。作为最简单的模模型，将环天线理想化为一个磁偶极子，电离层理想化为具有锐边界均匀各向异性等离体，分析计算了ＶＬＦ环天线在海面上产生的场。     

异形场发射分米波电视

异形场发射分米波电视孙甲虎（陕西宝鸡电视台７２１０００电视发射机的载波频率工作在甚高频（ＶＨＦ）或特高频（ＵＨＦ）频段，其传播方式是靠空间波传播的，近似于光波的传播特性。传播的视距距离由电视发射机输出功率和发射天线高度决定。当发射机的输出功率确定时，...     

低纬电离层闪烁与扩散F

同步卫星４ＧＨＺ电视信号和ＶＨＦ信标信号电离层闪烁与其附近的电离层扩散Ｆ资料进行比较，说明低纬电离层闪烁与扩散Ｆ有关正相关关系。     

INTERBALL—2卫星MEMO实验观测结果的初步分析

利用ＩＮＴＥＲＢＡＬＬ－２卫星上多分量波测量实验（ＭＥＭＯ）在ＥＬＦ／ＶＬＦ／ＬＦ三个频段进行的高分辨率等离子体波观测结果。通过事件分析，给出了所观测到事件的波传播特性的估值。结果表明：对于极区千米波辐射（ＡＫＲ），Ｒ－Ｘ模式和Ｌ－Ｏ模式可以同时发生。前者在低频段，后者则发生在频率高端，两者传播是在准平行于地磁场方向的波法线方向上。ＶＬＦ嘶声发射表明主要是哨声模式，但其它模式也存在。利用波特性分析     

VHF／UHF收信机指标和测试方法（续）

ＶＨＦ／ＵＨＦ收信机指标和测试方法（续）国家无线电监测中心陈霞生，尹纪新七、传导杂散发射１．指标具有匹配的天线端上测量任何离散频率的杂散发射功率应该不超过２．０ｎｗ。２．定义杂散发射是发射机关闭状态下，从接收机出来的任何发射。３．测试方法（ｌ）杂散发...     

大屏幕彩电的端子知多少

电视机要接收信号就得有输入端子，而要输出信号则要有输出端子。大屏幕彩电为满足家庭影院的需要，输入输出端子比一般彩电有了更多的扩展，以保证与其外围ＡＶ设备的正常连接，使之功能发挥得尽善尽美。大屏幕彩电主要配置的输入输出端子有：１．天线输入端子天线输入端子又ＵＯ射频（ＲＦＲａｄｉｏＦｒｅｑｕｅｎｃｙ）输入端子。它通过阻抗变换器与室外天线或者电视机上的接杆天线相连，可接收空中的无线电视节目；与室内的闭路电视（ＣＡＴＶ）系统相连，就可以接收有线电视网络中的节目；还可以与录象机、ＬＤ、ＶＣＤ或者ＤＶＤ的Ｒ…     

CATV共用天线放大器前端立柜介绍

本文介绍了ＣＡＴＶ大功率共用天线放大器前端立柜，它采用了ＶＨＦ／ＵＨＦ分频道先放大、后混合的方案，解决了ＶＨＦ／ＵＨＦ频道间隔离度差的难题，输出功率大，是大系统共用天线理想的前端设备。     

高频地波雷达的电离层杂波识别新试验

为了验证电离层杂波干扰的存在及研究其对高频地波雷达性能的影响,武汉大学电波传播实验室在浙江舟山东沙试验基地利用高频地波雷达完成了电离层杂波干扰识别新试验.试验采取改变地波雷达发射天线结构即改变发射天线的波束指向,使得电磁波垂直向上发射,进行电离层垂直探测试验;同时也有部分能量向海洋传播,从而获得海面Bragg散射回波.与此相对应地采用垂直极化的三元八木天线向海洋表面发射电磁波,同时获取海洋回波与电离层杂波.详细介绍了试验过程并对实测结果进行了初步分析,并介绍了新近研制的便携式高频地波雷达OSMAR-S的系统结构及其工作参数.     

天线高度对中波发射效果的影响及适配改造实践

本文通过分析中波广播的实际发射效果，对天线输入阻抗与桅杆天线高度的关系进行了研究，提出了一种降低天线高度进而提高高频段发射网络阻抗匹配度，提升中波信号有效发射半径、改善信号接收强度的方法。     

新品快递

安捷伦推出新款光纤收发器安捷伦科技公司为千兆以太网、ｉＳＣＳＩ（网际协议小型计算机系统接口）和光纤通道开发出了３款小封装可插拔（ＳＦＰ）光纤收发器。这些新款收发器的电磁干扰（ＥＭＩ）辐射达到了业内最低水平 ,使网络设备制造商可以在系统中同时采用２００多支安捷伦ＳＦＰ收发器 ,端口密度比其它ＳＦＰ解决方案提高了８倍。安捷伦推出的这３款收发器分别是ＨＦＢＲ -５７１０Ｌ、ＨＦＢＲ -５７０１Ｌ和ＨＦＢＲ -５７３０Ｌ ,它们的工作电压为３．３Ｖ ,采用波长为８５０ｎｍ的氧化物ＶＣＳＥＬ（垂直腔表面发射激光器）光源…     

基于全波法的甚低频波对低电离层扰动分析

通过全波解反射系数和波模振幅递归算法,文中分析了平面波在水平电离层分层结构中的能流分布规律,结合电离层化学反应模型对电离层参量的扰动情况进行仿真,并与其他文献中使用的方法相比. 全波计算方法考虑到了各层反射、透射波相互叠加的情况,仿真结果对比发现,用全波法得到的能流吸收和电子温度扰动幅度更大. 不同入射波参数、地磁场参数、电离层背景参量下的扰动情况对比发现:改变电波入射角会使电离层中电波的反射吸收高度发生变化;改变方位角和地磁倾角仅影响电离层能流吸收幅度,不会对电波反射高度造成影响;改变中性成分的浓度和温度会影响电离层的能量损失和化学反应过程.     

Radiation from a generalized antenna in a stratified medium

Exact calculations are made of the electromagnetic field radiated by an arbitrary current distribution in an arbitrary stratified lossy medium. The medium thus characterized can include both a stratified earth and a many layer stratified ionosphere. The results of the investigation, which include the input resistance and the efficiency of the antenna, are useful for designing antennas in the ELF, VLF and LF bands. (The theory is applied to the case of an ELF-ring antenna.)     

T型甚低频多调谐发射天线电容与电感研究

甚低频天线理论认为,采用多调谐方式,T型甚低频多调谐天线可以基本按比例增加天线电容,在实际工程中常用五组或六组天线.本文利用甚低频天线输入电抗的实测值,计算了在不同频率下天线所呈现的等效电容和等效电感,研究了T型甚低频发射天线的等效电容、电感、功率容量与天线组数及频率之间的关系.研究结果表明T型甚低频多调谐天线的组数过...     

计算电离层VLF波传输特性的时域有限差分算法

在星载甚低频( VLF)通信技术中,研究甚低频信号在电离层中的传输特性具有重要意义。现有的利用时域有限差分( FDTD)算法研究电离层传输特性大多基于高频脉冲信号,且传播模型相对粗略,计算存在一定误差。为此,建立了更为精确的电离层各向异性传播模型,对常规的FDTD算法引入变步长因子,并用该算法对VLF波在电离层中的场强衰减进行了数值计算,研究了昼夜变化及频率对其传输特性的影响。仿真结果与卫星实测数据对比表明：与常规的FDTD算法以及全波分析方法相比,引入变步长因子的FDTD算法精度更高;在VLF频段,降低频率有利于电磁波穿透电离层,且白天的衰减明显大于夜间;VLF波在射入电离层并穿透D层时衰减严重(30~40 dB),约为F1层中衰减的3倍。     

甚低频系留气球缆绳天线设计实现与效能分析

甚低频系留气球缆绳天线是机动式车载甚低频通信系统的重要组成部分. 该缆绳在作为气球浮空平台系留缆的同时,还需兼具甚低频段电磁波的天线辐射功能. 本文针对甚低频辐射天线的电气特性及物理特性,通过对天线关键参数的计算、不同风速下的缆绳姿态及辐射方向图的设计仿真,在工程上以光电复合系留结构形式进行实现。最终结合理论分析与全系统通信试验数据对甚低频系留气球缆绳天线的辐射效能做出了综合评估,验证了该天线设计的正确性与高效性,为国内甚低频辐射天线的相关研究积累了一定的经验与数据.     

Very-low-frequency propagation below the bottom of the sea

Radio-wave propagation at very low frequencies (VLF) in the stratified rock below the bottom of the sea is studied. A reasonable assumption of extremely low electrical conductivity in the stratified rock is based upon available geological data. The surface wave traveling along the interface between this region of low conductivity and the highly conducting sea is compared with the vertically polarized ground wave found in VLF radio-wave propagation at the surface of the earth. When extremely low frequencies (ELF) are transmitted, the highly conducting layer found at greater depths below the bottom of the sea forms the lower surface of a spherical waveguide. This waveguide at ELF supports a propagation mode similar to the mode existing at VLF between the surface of the earth and the lower boundary of the ionosphere. The similarity in propagation mechanisms leads to the name "inverted ionosphere" (described by Wheeler [1]) for the underground region. The sea or relatively highly conducting soil at the surface of the earth is an almost impregnable shield against atmospheric noise and effects from sudden ionospheric disturbances or solar flares. In addition to providing a noise-free medium, the sea has the advantage that construction costs are much less than those of a VLF transmitter at the earth's surface. Presumably communication between shore installations and submarines on the floor of the ocean could be achieved with the inverse ionosphere. The power requirement for such communication with existing VLF transmitters at the earth's surface renders such transmission unattainable.     

Primary VLF/ELF currents produced by heating the lower ionospherein parts of China

A new iterative method is employed to calculate the primary ELF/VLF currents produced by heating the lower ionosphere with powerful modulated waves. The calculations are mainly for parts of China, as well as For Tromso, Norway for comparison. The results indicate that first, there are many similar characteristics for Beijing and Tromso, secondly the ELF/VLF currents in Haikou are much larger than those in Beijing and Tromso if the natural electric fields are equal     

Radio Emission of the High-Latitude Ionosphere as a Result of the Cutoff Mode of the Auroral Ionospheric Duct

Issues of radio emission of the auroral ionosphere are considered with the use of the classical electrodynamics approach, according to which a natural waveguide is formed in the Earth’s ionosphere owing to formation of a trough in the high-latitude ionosphere. Parameters and characteristics of the auroral ionospheric dielectric duct have been estimated on the basis of the obtained experimental data on the properties of the ionospheric trough. The hypothesis that the LF and VLF electromagnetic auroral radio emission in the high-latitude ionosphere is due to the approach of the auroral waveguide to the cutoff mode has been considered. It has been found that the radio emission bands correspond to the eigenmodes of the ionospheric duct under consideration. It has been shown that, within the proposed approach, not only the radio emission frequency band of the high-latitude ionosphere but also the polarization of the radio emission observed in the experiments can be explained.     

Broad-band analysis of VLF/LF aircraft wire antennas

The broad-band response of a VLF/LF dual-wire aircraft antenna is analyzed. The impedance properties and the induced currents on the two wires of different lengths are obtained via a superposition procedure in which the original problem is split into two transmission-line (differential-mode current) problems and two antenna (common-mode current) problems. Results for the input admittance and short-circuit current of a representative VLF/LF dual-wire antenna are presented.