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1、专专 业业 英英 语语Keywords:aerial adj.天线的 n.天线 e.m.wave 电磁波 convey vt.传递 the morse code 莫尔斯电码 in a controlled way 有控制的 bang n.响声 Quality of Service 服务质量 Service Status 服务状态 专专 业业 英英 语语Keywords:Float Type 浮点型（数据）=single sideband 单边带 reinsert n.重插入 take place 发生 allow for 考虑到，允许 multiply v.乘，扩大 Intersymbol I
2、nterference 码间干扰 Auxiliary Equipment 辅助设备 专专 业业 英英 语语Keywords:in the case of 在情况下foresight n.远见look like 看起来象prone(to)adj.易于的 Payphone 付费电话 Payload 负荷 payloadpointers 负荷指针Appendix 附录专专 业业 英英 语语Keywords:Coverage 覆盖Coverage Area 覆盖范围,覆盖区,有效区 Interference 干扰Preliminary Design 概要设计,初步设计 Jam-to-signal ra
3、tio 干扰信号比 Interferer diversity 干扰源分集 Interference-Adaptive System 干扰自适应系统 专专 业业 英英 语语Keywords:感应电荷 Inductive charge 高保真度音响 High Fidelity高层兼容性 High Layer Compatibility 高电位差 High potential difference高频 High Frequency（HF）高增益天线 High gain antenna 高增益功放板 High gain Power Amplifier board 告警面板 Alarm panel 专专
4、 业业 英英 语语Keywords:告警模块 Alarm module 格式转换 Format Conversion 隔行扫描 Interlace Scanning 个人编码 Personal Number 个人识别码 Personal Identity Number 工程手册 Engineering Manual 工具软件 Tool Software 个人通信网，专用通信网 Personal Communications Network专专 业业 英英 语语Keywords:工业水平尺 Industrial horizontal ruler 工作波长 Working wavelength 工
5、作单元 working unit功率分配结构 Distributed Power Architecture 公用密钥,公开密钥 Public key 供参考 For reference 共享内存 Shared Memory 共享资源 Shared Resource 专专 业业 英英 语语Keywords:规程 Procedure规定容限,可接受容限 Tolerance规范和描述语言 Specification&Description Language SDL 规则脉冲激励长期预测 Regular Pulse Excited Long-Term Prediction 硅钢片 Silicon St
6、eel Sheet硅谷 Silicon Valley硅控整流器 Silicon Control Rectifier专专 业业 英英 语语Keywords:骨干网 Backbone Network固定比特率 Constant Bit Rate 固定卫星业务 Fixed Satellite Services 固定信道分配 Fixed Channel Allocation 固态继电器 Solid-state Relay 故障,错误 fault,error，failure,Bug 故障定位 Fault locating 故障申告受理 Fault Complaint Handling 专专 业业 英英
7、语语Keywords:光探测器 Photodetector光开关 Optical Switch光缆 Fiber Optic Cable光连接器 Fiber Connectors光滤波器 Optical Filters光敏电阻 Optical Resistor 光耦合器 Optical Couplers 光收发模块 Optical Transceivers 专专 业业 英英 语语Keywords:光通道 Optical channel 光网络单元 Optical Network Unit 光无源器件 Optical Passive Devices 光纤 Optical Fiber/Optic f
8、iber 光纤包层 Cladding of Fiber 国标 National Standard 国际电信联盟 International Telecommunications Union 国内长途号码 National Toll Number 专专 业业 英英 语语If a transmitting aerial radiates a constant amplitude e.m.wave it conveys little information to the receiver.transmit发射，传播 aerial天线 radiate辐射 constant常量，不变的 amplitud
9、e振幅 e.m.wave=electromagnetic wave 电磁波 convey传达 receiver接收者，接收机专专 业业 英英 语语 The simplest way of sending information is to switch the transmitter on and off so that a series of dots and dashes are transmitted-the morse code for example.This is a very common method of communicating between ships at sea,
10、but it does require the operator to read the code.switch on(off)开（关）a series of一连串的 morse code莫尔斯电码 operator话务员专专 业业 英英 语语Any process of superimposing some pattern on the continuous e.m.wave which allows information to be carried is called modulation.We say the carrier wave is modulated.To modulate
11、a carrier wave all we need to do is to vary a property of the wave in a controlled way.superimpose迭加 modulation调制 carrier wave载波 property特性，性质 in a controlled way有控制地专专 业业 英英 语语 Thus,if we vary its amplitude we produce amplitude modulation(a.m.),if we vary its frequency we produce frequency modulati
12、on(f.m.),and if we vary its phase we have phase modulation.(p.m).vary改变 amplitude振幅 amplitude modulation(a.m.)调幅 frequency频率 frequency modulation(f.m.)调频 phase相位 phase modulation(p.m.)调相专专 业业 英英 语语Generally,interferencefrom lighting or electrical machines-produces amplitude disturbances on an e.m.wa
13、ve passing by.干扰是在光电产品中,伴随着电磁波的传播而产生幅度的干扰 Because the amplitude of f.m.carrier is not carrying information，调频载波幅度并不承载信息such interference has very little effect on the received signal.This is not the case with an a.m.carrier,但是调幅载波就不一样了，where all such bangs and crackle are detected at the receiver as
14、 information.interference干扰 amplitude disturbance振幅波动 received signal 接收信号 bang巨响 crackle劈啪响专专 业业 英英 语语On the other hand the bandwidth of the a.m.carrier is much less than that of the f.m.carrier as we shall now show.下面将给出例子 on the other hand另一方面 bandwidth带宽 much less少得多专专 业业 英英 语语If we modulate a 1
15、00kHz carrier with a 1kHz signal，it might be expected that although the carrier amplitude would miss and fall in step with the amplitude of the 1kHz signal the carrier frequency would remain at 100kHz.尽管载波幅度回损失和下降到与一致,但其频率仍有期望保持在In fact two new frequency components can be detected in the modulated c
16、arrier;they are 101kHz and 99 kHz.in step with与同步 remain保持 component成分 modulated carrier调制波专专 业业 英英 语语Thus a carrier of frequency fc,amplitude modulated with a signal of frequency fs 当一个载波频率为 信号频率为的幅度信号调制包含三个频率contains frequencies fc,fc+fs,fc-fs.The last two are called sidebands.Fig.5.1 is the frequ
17、ency spectrum of an a.m.carrier.sideband边带 frequency spectrum频谱 a.m.carrier调幅载波 专专 业业 英英 语语Fig.5.1 The carrier and sidebands of an a.m.signalbandwidthcarrierLower siderband upper siderband2ffc-fs fc fc+fs专专 业业 英英 语语The carrier componentremains at constant amplitude and is not conveying information(e
18、xcept about its own frequency).载波的成分保持在一个固定的幅度且并不传播信息 It represents wasted transmitter power.Sometimes it is not radiated没 有 辐 射-then we have a suppressed carrier a.m.transmission.抑制Sometimes only the carrier and one sideband are radiated,sometimes only one sideband(s.s.b=single s.b.).represent表明was
19、ted浪费，消耗suppress抑制 transmission传输专专 业业 英英 语语If less than the full a.m.carrier完全振幅调制载波 is transmitted the receiver needs to be more complicated to receive it,接收非常复杂 because basically the carrier must be reinserted at the receiver before detection can take place.在检波前要重新再植入一个载波 less than小于 complicated复
20、杂的 reinsert重新插入 detection检波专专 业业 英英 语语In a.m.the full bandwidth在振幅调制里一个完全的带宽 is from fc-fs to fc+fs,i.e.2fs so that for a speech transmission where voice frequencies extend up to 3kHz-we should need 6kHz of bandwidth;for music 30kHz needed.bandwidth带宽 i.e.也就是 speech transmission音频传输 extend up to增加到专
21、专 业业 英英 语语Transmitters should be spaces apart in frequency to allow for these bandwidth requirements.There are international agreements about frequencies but they are not observed by all countries.transmitter发射机 space apart空间分离 allow for虑及，考虑到 bandwidth requirement带宽要求 international agreement国际协议 ob
22、serve遵守专专 业业 英英 语语For the mathematically inclined it is easy to show that the sinusoidal modulation of the amplitude of a sinusoidal wave-form results in the production of sum and difference frequencies.inclined倾向 sinusoidal modulation正弦调制 sinusoidal wave-form正弦波形 result in导致，体现专专 业业 英英 语语 Suppose w
23、e have an un-modulated carrier(fc)of the form a=Asin(2fct)where a is the instantaneous amplitude and A is the maximum amplitude,often simply referred to as the amplitude of the carrier.Now let us modulate A sinusoidally at a frequency fs,and write.suppose假设 un-modulated未调制 instantaneous amplitude瞬时值
24、 maximum amplitude最大值 sinusoidally正弦地专专 业业 英英 语语 a=A1+ksin(2fst)sin(2fct)k is a constant multiplying out we get a=A sin(2fc t)+Aksin(2fs t)sin(2fct)=Asin(2fst)+AK/2cos(2(fc-fs)t)-cos(2(fc+fs)t)=carrier+AK/2lower sideband-upper sideband multiply out乘 lower sideband下边带 upper sideband上边带专专 业业 英英 语语When
25、 k is 1 we have 100%modulation,for the two sidebands each of amplitude A/2 can combine to make the total amplitude vary from zero to 2A.“for”引导原因状语从句；“When k is 1”是时间状语从句；“each of amplitude A/2”则是后置定语，修饰“sideband”。专专 业业 英英 语语In the case of f.m.a mathematical analysis of the modulated carrier is more
26、 difficult than for a.m.and would involve us in Bessel functions.mathematical analysis数学分析 modulated carrier（已）调制载波 Bessel functions贝塞尔方程 involve in涉及专专 业业 英英 语语Bessel was a nineteenth century mathematician who had the foresight to solve the very equations we need for f.m.So we can go straight to th
27、e end of the mathematical process and find that a frequency modulated carrier has many more sidebands than has one which is amplitude modulated with the same signal.Take the case of the 100kHz carrier and the 1kHz signal;the spectrum for f.m.might look like Fig.5.2.mathematician数学家 foresight远见 very正
28、好，恰好“has one which is amplitude modulated with the same signal”为倒装。专专 业业 英英 语语Fig5.2 The carrier and some of the sidebands of a f.m.signalfc-3fs fc-2fs fc-fs fc fc+fs fc+2fs fc+3fsBandwidth在F位置专专 业业 英英 语语Obviously the bandwidth for a f.m.carrier is much greater than for a.m.and this is part of the price we pay for a transmission much less prone to interference.Transmission employing f.m.must therefore be spaced(in frequency)further apart than for a.m,and in these days bandwidth is at a premium and in very short supply.transmission传输 prone to易于的 at a premium非常珍贵 in very short supply相当缺乏