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Letter Writing Practice 2 Test Yourself You office needs to rent a video camera for one month. You need a small machine that produces a professional quality image. Write to Photofinish Ltd and ask them if they rent machines like that and the price. Write a full business letter. (invent any details you need)
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习题一:1-4,1-5,1-6,1-7,1-9AD1-1 CAD1-1:用非线性VCVC实现一个幅度调制电路,如题图 CAD101所示。输入信号为两个不同频率的信号和, 输出实现两信号相乘,即EMOD=V1*V2。 设v1是50kHz的正弦信号,2是1kHz的调制信号。 要求得到标准调幅波SAM(调幅度mA=0.3和1.0) 抑制载波调幅波scAM 幅度键控调幅波ASK 并分析上述三种调幅波的特点
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1) provide some clues to what makes a Nobel Prize Winner. 2) give guidance to learners to listen and talk about famous person. 3) provide students with new words and expressions 4) learn how to analyze word formation 5) ask learners to write in a chronological sequence
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4.3.1 ASK或PAM信号传输的最佳检测和错误概率 4.3.2 PSK信号传输的最佳检测和错误概率 4.3.3 QAM信号传输的最佳检测和错误概率
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In this unit, you will first listen, and then learn to ask about job opportunities and go for job interviews; read about online job applications and first job experiences; learn new words and expressions; write your own résumé; visit Culture Salon for some new terms in careers; check goals
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Problem 1. The following two parts are not related. Try them, to make sure you un- derstand the jargon of random variables distributions, probability density functions, etc. Ask your TA if you don't understand/remember what some phrase means. (a)Suppose X1, X2, and X3 are three mutually independent random variables, each having the uniform distribution
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Unit 8 II. Listening Skills To keep our children safe from those dangerous criminals, these tips might be helpful. First children should be encouraged always to ask permission from their caregiver before they go anywhere. They should not only tell the care giver where they will be at all times, but also who will be looking after them. also, children should never walk or ride their bikes alone. Instead, they
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数据通信基本概念 数据通信系统基本结构 信息、数据、信号 数据通信的主要技术指标 数据传输方式 串行通信、并行通信 单工通信、半双工通信、全双工通信 基带传输、频带传输、宽带传输 数据的同步技术 异步传输、同步传输 数据编码技术 数字数据信号 模拟传输 幅移键控ASK、频移键控FSK、 相移键控PSK 数字传输 不归零码NRZ、曼彻斯特编码、 差分曼彻斯特编码 模拟数据信号 模拟传输 调幅、调频、调相 数字传输 脉冲编码调制PCM 多路复用技术 时分多路复用、频分多路复用、波分多路复、码分多路复用 数据交换技术 电路交换、报文存储转发交换、报文分组存储转发交换(数据 报方式、虚电路方式) 传输介质 传输介质类型与特点 差错控制技术 检错码、纠错码和差错控制机制
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1、确知信号和随机信号 ①确知信号是指它经过恒参倍道后的参数(幅度、频 率、相位、到达时间等)都是确知的。如数字信号,从检 测的观点来看,未知的仅是信号的出现与否。 ②随机相位信号,这种信早除了信号的相位严之外, 其余参数都是确知的,即信号的相位是唯一随机变化的参 数。它的随机相位在数字信号的持续时间(T)区间内为 某一值,而在另一个时间间隔内为另一值。这种变化是随 机的。例如FSK和ASK信号等。这种信号的相位分布, 一般认为p在[o,2区间内是均匀分布的
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