Propagation Along a Braided Coaxial Cable in a Circular Tunnel

The modes of propagation along a coaxial structure contained within a circular tunnel are considered. The primary objective is to develop an approximate impedance boundary condition at the outer surface of the shielded cable that can be used in previously developed formalisms for axial conductors in tunnels. It is assumed that the metal braid can be characterized by a surface-transfer impedance. We also account for the possibility that a Iossy film exists on the outer surface of the dielectric jacket of the cable.     

Calculated Channel Characteristics of a Braided Coaxial Cable in a Mine Tunnel

The braided coaxial cable is studied as a communication scheme in a mine tunnel. A simplified rectangular waveguide model is adopted for the tunnel, and the shield of the cable is assumed to behave as a single inductive transfer impedance. Specific results on the attenuation of the monofilar and bifilar (or coaxial) modes of propagation, taking into account the possible existence of a thin lossy film on the cable, are presented. In order to estimate the maximum possible range of communication, we consider the coupling factors of these modes to transmitting and receiving dipoles inside the tunnel, and we present results on these factors for various cable parameters and over a wide range of frequencies.     

Propagation Along a Braided Coaxial Cable Located Close to a Tunnel Wall (Short Papers)

A previous development is extended to permit attenuation calculations when a braided cable is located close to a tunnel wall. This is an important case in mine communications utilizing leaky feeders. Numerical results are presented to illustrate the effects of numerous parameters on mode attenuation. A principal finding is that the attenuation rate for the bifilar mode is hardly affected at all by the finite conductivity of the wall. On the other hand, the monofilar mode suffers a very high attenuation when the cable approaches the wall.     

疏编织漏泄同轴电缆空间场分布的研究

通过对SLYWV-75-10型疏编织漏泄同轴电缆的空间场分布进行实际测量,并对测试结果和数据进行分析,证明SLYWV-75-10型疏编织漏泄同轴电缆完全能够作为户外周界入侵探测报警系统的探测传感器,同时对电缆间距、最大单元警戒范围以及系统的响应时间等给出了具体的参考指标,对户外周界入侵探测报警系统的研制和开发具有重要指导意义.     

Electromagnetic Theory of the Loosely Braided Coaxial Cable: Part I

A solution to Maxwell's equations subject to boundary conditions on counterwound helical wires is achieved. The helices are contained in a cylindrical surface that is concentric to a perfectly conducting center conductor of circular cross section. The permittivity of the annular region may be different from that of the external region. The excitation is taken to be symmetrical about the cable which leads to a considerable simplification of the formulation. The key step is to recognize that the assumed form of the current on the thin helical wires is a spatial harmonic expansion that leads to a doubly infinite expansion, in such harmonics, for the resultant fields. The inherent complication of the problem results from the intercoupling between the spatial harmonics of the helix currents. Various generalizations of the theory are also indicated.     

电视信号在同轴电缆中的传输

从理论到实践分析了有线电视系统中由同轴电缆引起的一些特殊故障，它是在有线电视系统升级改造与维护工作中常被忽视的技术问题。     

Electromagnetic Theory of the Loosely Braided Coaxial Cable: Part II--Numerical Results

The general modal equation obtained in Part I is solved numerically for the propagation constants of both the monofilar and bifilar modes. For the special case of an air-filled cable, only one mode is supported. Numerical results are also presented for the surface transfer impedance of the shield which, in general, depends on the propagation constant. The properties of the counterwound helical shield are found to be qualitatively similar to those of the unidirectional helical shield.     

Effect of Ripple Taper on Coupling Modes in a Coaxial Bragg Structure

Based on the mode-coupling method, numerical analysis is presented to demonstrate the influence of ripple taper on coupling modes on the frequency response in a coaxial Bragg structure. Results show that the interval between the band-gaps of the competing mode and the desired working mode is narrowed by use of a positive taper, but is expanded if a negative taper is employed, and the influence of the negative taper is more obviously advantage than the positive taper. The residual side-lobes of the frequency response on coupling modes can be effectively suppressed by employing the windowing-function technique. These characteristics of a tapered coaxial Bragg structure are favorable to improvement of the performance as a reflector or a filter in its application, also favorable to the mode selectivity and further weaken the excitation of unwanted spurious modes.     

RF同轴电缆传输系统的设计与维护

介绍同轴电缆的结构与传输特性、射频传输干线与分配网络设计技术.     

漏泄同轴电缆耦合损耗特性评定的探讨

除长度耦合损耗(Lc,50、Lc,95)值外,增加Lc,95-Lc,50值、天线三向Lc,95值、Lc,95耦合损耗圆图及其不圆度参量,扩展了IEC标准中的"耦合损耗",全面评定漏泄同轴电缆辐射电场特性。实例分析讨论不同结构漏泄同轴电缆辐射电场特性。     

双馈电视发射系统中同轴馈管的更换方法

为提高安全性,电视发射系统中多采用双馈管的形式。本文介绍了苏州台一根馈管故障后,进行更换新馈管的方法。本文通过测试驻波比,得到计算误差小于一个波长的新馈管大概长度;再测量两个馈管的S11参数的相位,并消除其中的相位模糊问题,精确计算出新同轴馈管的长度。最后通过调整新馈管长度,该方法使新旧馈管等长。     

影响大功率射频同轴电缆功率传输的因素

大功率射频同轴电缆主要用于广播电视发射系统和雷达系统的功率传输,一般采用空气绝缘、皱纹管导体结构,额定平均功率是其重要性能参数。简单介绍了大功率射频同轴电缆的结构、额定平均功率的计算,结合实际应用分析了影响大功率射频同轴电缆功率传输的因素,介绍了大功率射频同轴电缆选用时的注意事项。     

VQ Digital Video Transmission through Coaxial Cable using OFDM

Transmission of high definition digital video (HDTV) by satellite, cable (CATV), and optical networks is an area of intense activity, specially in Europe and North America, where the main challenge is to increase the number of TV channels in the assigned spectrum. In this paper, OFDM modulation is studied for HDTV transmission on a 6 MHz bandwidth channel by using coaxial cable as a transmission medium. Attenuation, phase shift and propagation time are considered, as well as the prevailing degradations on CATV: thermal noise and crosstalk. We compress the video source information in terms of the Vector Quantization (VQ) technique, which is found to be very robust against channel errors. According to our results, we give some recommendations about the design of the filters required in the system and the minimum frequency guard bands between adjacent channels.     

Influence of Spatial Dispersion of the Shield Transfer Impedance of a Braided Coaxial Cable (Letters)

The effect of the dependence of the braid transfer impedance on the propagation constant is discussed for a coaxial cable located in a circular tunnel.     

800 Mbit/s Digital Transmission System Over Coaxial Cable

800 Mbit/s digital transmission systems, using nonredundant three-level and four-level codes, have been studied as a means of providing an economically attractive digital transmission system. These systems have been designed to be compatible with a 60 MHz analog system in repeater spacing and repeater size, so as to be easily introduced into the existing network. These systems with 11 520 telephone channels, exceed the 60 MHz analog system in both capacity and economy. Due to repeater construction factors, it became clear that the three-level code is more suitable. This paper describes the design and performance of 800 Mbit/s digital transmission systems and repeaters.     

Improvement of Transmission Characteristics of Superconductive Coaxial Cable: Spectral Analysis of Dimensional Irregularity of Raw Materials of Coaxial Cable

This paper deals with the improvement of the transmission characteristics of superconductive coaxial line (SCCX), and presents a quantitative relationship between the Fourier component of the dimensional irregularities in the raw material of SCCX, such as the thickness of the copper tape and the diameter of the insulator, and an abnormal increase of the transmission loss due to the periodic impedance irregularities. This paper also shows that even for the coaxial cable with very small attenuation constant (≈ 0.5 dB/km) and high operating frequency (up to several gigahertz), an approximate formula for loss peak due to the periodic impedance irregularities holds for the production length of cable. This is indicated by the comparison of an approximate formula with the result of digital computer simulation.     

八字形槽漏泄同轴电缆耦合损耗仿真分析

广泛应用于地铁、隧道、地下商场、矿井等闭域空间的漏泄同轴电缆,因不同应用环境对其电气性能要求不同,因此分析影响漏泄同轴电缆耦合损耗等电气性能的因素、探索其变化规律,具有重要的工程应用价值。文中分析了八字形槽孔漏泄同轴电缆耦合损耗随槽孔角度、长度和槽孔节距的变化规律,提出保持单八字形槽孔对几何结构参数不变,仅改变相邻八字形槽孔对之间距离的槽孔节距调节方法。给出了采用此种方法的实际设计算例,仿真结果与实测结果吻合。     

圆形隧道中泄漏同轴电缆辐射场的FDTD 分析

随着泄漏同轴电缆在各种闭域空间中的应用越来越广泛,其精确的辐射特性数值解也引起人们的关注。在圆柱坐标系下,根据泄漏同轴电缆的辐射理论,分析了圆形隧道中电磁波的传播途径,用时域有限差分（FDTD）方法求解了泄漏同轴电缆在圆形隧道中的辐射场。该方法相比于解析法,简化了计算程序,提高了结果的精确度,并且易于实现。 仿真结果表明在圆形隧道中,泄漏同轴电缆不存在传统天线所具有的通信盲区的缺点,可以实现与外部空间的全方位双工通信。     

Propagation Along a Coaxial Cable with a Helical Shield

A leaky coaxial cable is modelled by a dielectric coated conductor shielded by a finite number of unidirectional helical wires. A modal equation is derived and soIved numerically for the propagation constants of both the monofilar and bifilar modes. Numerical results are also presented for the effective surface transfer impedance of the shield. This parameter is found to depend, in general, on the propagation constant.