在CATV系统中如何选用放大器

放大器是有线电视系统中最重要的部件之一,广泛应用于系统的前端、干线传输和用户分配网络。由于放大器是在满足载噪比和非线性失真的各项指标的前提下,尽可能把输入端的弱信号放大,输出足够高的电平,其性能的好坏直接影响到系统的质量,因此必须选择经国家广电总局认定的产品。选择放大器,首先要考虑它的工作频率范围是否合乎要求,例如在550MHz系统中的干线放大器,其工作频率范围为45～550MHz等等;其次考虑其输出电平,最大输出电平越大越好;还要考虑它的增益,即输出信号是输入信号的倍数;还有噪声系数应越小越好;反射损耗越大越好。特别是非线性失真指标,例如交调、互调等指标,都应越大越好,即失     

谈谈CATV系统的分配效率

一、前言 分配系统主要是将干线系统传送来的信号分配至各用户。分配系统的设计主要考虑的是高效率的电平分配。为了获得高的分配效率,分配系统的放大器应工作在高电平状态。因此,势必造成分配系统载噪比[C/N]指标随着放大器台数n的增加以10lgn的规律下降,交调比[CM]随着放大器台数n的增加以20lgn的规律下降,随着传输频道数N的增加以15lgn(N—1)的规律下降。为了保证系统的[C/N]、[CM]指标。要求放大器的输入电平随着放大器台数n的增加而增加10lgndB,而输出电平随着放大器台数n和传输频     

CATV系统的分配效率

ＣＡＴＶ系统的分配效率山东招远市人民广播电台阎春学１前言分配系统主要是将干线系统传送来的信号分配至各用户。分配系统设计主要考虑的问题是高效率的电平分配。为了获得高的分配效率，分配系统的放大器应工作在高电平状态。因此，势必造成分配系统载噪比［Ｃ／Ｎ］指...     

CATV系统的分配效率

1前言分配系统主要是将干线系统传送来的信号分配至各用户。分配系统设计主要考虑的问题是高效率的电平分配。为了获得高的分配效率，分配系统的放大器应工作在高电平状态。因此，势必造成分配系统载噪比（C／N）指标随着级联的放大器台数n的增加以101gn的规律下降，交调比（CM）随着级联的放大器的台数n约增加以201gn的规律下降，随着传输频道数N的增加以151gn（N-1）的规律下降。为了保证系统的C／N、CM指标，要求放大器的输入电乎随着放大器台数n的增加而增加IOlgnIB，而输出电平随着放大器台数n和传输频道V的增加而降低［IOlgn＋…     

CATV系统主要技术参数的测量

简要叙述了GATV系统中电场强度与电平、频率特性、栽噪比、互调比、交扰调制比的测量方法。     

CATV干线平坦度分析

1 前言在调试CATV干线系统时,根据设计要求将干线放大器输出幅度调在规定的电平上,以满足载噪比、交调、互调、CTB等技术指标要求,在终端获得良好的电视信号质量。但宽带的电视信号经过3～4个干线放大器之后,平坦度下降。出现明显的某段电平     

关于CATV系统中交调互调指标的分析

1前言随着CATV行业的逐步发展,我区有线电视网中的频道数越来越多,在系统性能指标中,交扰调制、相互调制等非线性失真将会给基带信号引入固定的干扰。因此,对有线电视工程技术人员而言,对交调、互调两项指标的理解显得尤为重要。2交调、互调的定义及公式交扰交调是指需要的调制信号电平的峰峰值和其它频道转移过来的调制信号电平的峰值比。CM=交扰调制比是表示由于系统非线性而造成各个频道的调制信号相互转移,影响用户正常收看的一项技术指标。载波互调是指载波电平有效值和互调产物电平有效值比。IM=载波互调比是表示由于系统存…     

CATV维修两例

故障现象：冬天,某小区各频道电视信号有条纹干扰,特高频段比甚高频段干扰明显,晚L比白人十扰明而。故障分析：此类故障是有线电视系统某级放大器失控,造成交互调干扰,产生非线性失真,产生的原因是因为冬天气温低,电缆的温度特性变化,超出放大器自动电平和自动斜?..     

CATV的设计和布局(二)

2 有线系统设计的基础因为选择电缆、放大器和耦合器/分配器是有一定的困难性,所以可以认为:是按照谨慎的设计规格和成本考虑,来作出这些选择决定的。有线系统的正常设计是从前端到系统的终端,设计时对系统的损耗和增益(信号电平)保持跟踪,以使每一个用户分支器具有在正确极限值范围内的信号电平。对于     

CATV电缆干线传输系统电平的合理设置

分析了 Ｃ Ａ Ｔ Ｖ 干线电平受载噪比和交调比的制约关系,给出了干线电平范围,对电平的效率均衡和均衡下“干放”的高低频道电平作了分析计算。     

Improved base station circular antenna array receiver for wireless CDMA systems

A Spatial interpolation technique for the upsampling of uniform circular arrays (UCAs), beyond spatial aliasing, is considered. The UCA interpolation algorithm is used as a preprocessing procedure in the reverse link to improve the performance of a cellular code division multiple access (CDMA) system. The motivation is to enhance the system's capacity and array resolution and reduce the fading and coupling effects with minimal receiver hardware and cost. At the base station, we propose to place the antenna elements uniformly on an imaginary circumference farther apart than/2, where is the free-space wavelength. The resulting UCA possesses superior resolution, less coupling effects than a corresponding UCA with the same number of elements and circumferential spacing less than or equal to/2, and possibly higher diversity gain. In order to increase the system's capacity and eliminate any spatial aliasing, we propose to interpolate the UCA to within the spatial Nyquist rate. This is achieved by placing a virtual antenna element halfway on the circumference between every two adjacent antenna elements. Simulations results are provided to support our claims.     

如何理解ISO／IEC17025：2005中“检测结果质量的保证”

通过对ISO/IEC17025:2005(检测和校准实验室能力的通用要求)中的5.9条"检测和校准结果的质量保证"的解释,作者较详细的阐述了实验室应如何通过质量控制措施来保证检测结果的质量,达到确保管理体系有效运行的目的。     

双激光场调控Be2+离子动力学的研究

为了研究高电荷态Be2+离子在强激光中的超快动力学过程,采用求解系统的密度矩阵的方法,进行了理论分析,获得了Be2+离子系统的光谱响应。结果表明,由于强激光场会导致激发态能级的瞬态斯塔克效应进而引起电子运动状态的改变,对应于Be2+离子系统跃迁偶极子的相位改变量为0.5π;当两束红外激光强度为0.94×1012W/cm2时,Be2+离子吸收光谱向高、低频端延伸,谱线形状由单个孤立的洛伦兹线型转化为“波浪式”结构;改变入射激光场的强度以及激光脉冲的持续时间和相对延迟时间可以控制吸收谱线型。此研究结果说明调控双激光的参量可以实现对高电荷态离子中核外电子运动的控制,也指明了软X射线脉冲整形的一个可行性方案。     

Thermal issues in microsystems packaging

Miniaturization of electronic/mechanical systems is achieved by packing different functional components into tight space. The heat transfer analysis for such systems has to deal with geometrically complex heat transfer paths, and it needs to be done quickly in response to every design alteration. This paper proposes a concept that aims at reduction of analysis load on the packaging designer. The proposed scheme is composed of two major steps. First, a computer program "configuration generator" is used to generate possible geometric configurations of heat transfer paths in a systematic manner. Second, temperature solutions for these configurations are compressed into "fast estimate" formulas that free the packaging designer from the need to perform involved heat transfer analysis. This approach is illustrated using a topic of heat spreading on the planar substrate as an example. Miniaturization of systems also raises another issue for the thermal design; that is the coupling between the system configuration and the overall heat dissipation to the environment. A model situation is considered where heat diffuses from a zone on the system shell and to the environment by natural convection and radiation. In the parametric domain spanned by the thermal conductivity of shell material and the system's characteristic length there is a zone where the system-level heat transfer is sensitive to the system's configuration. Such characteristic length is around 1 cm for systems encapsulated in plastics, 3-10 cm for those in ceramic and alloy shells, and 10-40 cm in copper or aluminum clad systems.     

WCFQ: an opportunistic wireless scheduler with statistical fairness bounds

We present wireless credit-based fair queuing (WCFQ), a new scheduler for wireless packet networks with provable statistical short- and long-term fairness guarantees. WCFQ exploits the fact that users contending for the wireless medium will have different "costs" of transmission depending on their current channel condition. For example, in systems with variable coding, a user with a high-quality channel can exploit its low-cost channel and transmit at a higher data rate. Similarly, a user in a code-division multiple access system with a high-quality channel can use a lower transmission power. Thus, WCFQ provides a mechanism to exploit inherent variations in channel conditions and select low-cost users in order to increase the system's overall performance (e.g., total throughput). However, opportunistic selection of the best user must be balanced with fairness considerations. In WCFQ, we use a credit abstraction and a general "cost function" to address these conflicting objectives. This provides system operators with the flexibility to achieve a range of performance behaviors between perfect fairness of temporal access independent of channel conditions and purely opportunistic scheduling of the best user without consideration of fairness. To quantify the system's fairness characteristics within this range, we develop an analytical model that provides a statistical fairness bound in terms of the cost function and the statistical properties of the channel. An extensive set of simulations indicate that the scheme is able to achieve significant throughput gains while balancing temporal fairness constraints.     

基于隐马尔可夫模型局部最优状态路径的数据重建算法

该文提出了基于隐马尔可夫模型局部最优状态路径的数据重建(LOPDI)算法。该算法假设语音特征矢量是一个L状态隐马尔可夫模型的输出序列,基于局部最优状态路径估计产生语音特征矢量的次最优状态序列,并按最大后验概率准则(MAP)重建出缺失矢量。实验表明,LOPDI算法能够显著提高语音识别系统对加性噪声的鲁棒性。     

全力提升BOSS与HLR接口处理能力

山东移动在"服务与业务双领先"战略的指导下,认真贯彻"让客户满意是我们不懈的追求"的服务理念,努力提升业务支撑水平,对BOSS与HLR接口系统进行了多次优化改造,从技术、管理等方面持续地全力提升系统处理能力,有效地避免了客户投诉,提高了客户满意度.     

基于概率加权平均的Mel子带特征重建算法

本文提出基于概率加权平均的Mel子带特征数据重建算法.该算法选择K个最优重建结果的概率加权平均作为被加性噪声掩蔽的语音特征分量的估计.实验结果表明,基于概率加权平均的语音特征数据重建算法降低了重建误差,减少了帧间突变现象,增强了Mel子带特征的帧间连续性,从而显著提高了语音识别系统对加性噪声的鲁棒性能.