techniques The that second are quite area employs different from those of conventional harfware require a substantial investment in designand and also special test equipment for efficient development quantity of information and debugging.The needed a worthy of a separate book and is not covered here.
数字设计可以分为两个总的领域。第一个领域是运用可用的构建模块直接创造和生产硬件。第二个领域是计算机软件或程序设计方面，它可以涉及或不涉及硬件方面。
第二个领域使用的技术完全不同与常规的硬件设计，为了有效地开发和调试还需要在专业测试设备上做大量的投入。这个领域所需要的信息量相当于一本单独的书，这里并不涉及。
二、The purpose of a receiver is to select a desired qroup of frequencies transmitter,get rid from of all unwanted one signals and noise,and then demodulate the signal to obtain the modulating information.The better the receiver does its job,the closer the resemble demodulate the oriinal signal signal from will the transmitter.Regardless of the type main of functions demodulate performed required,the by a receiver are filtering and amplifying.The receiver is the logical superheterodyne choice for the job.
接收机的目的是从一个发射机发射的信号中选择一组期望的频率，去除所用不需要的信号和噪声，然后解调信号获得调制的信息。接收机做的工作越好，解调的信号与发射机发出的原始信号就越接近，不论需要什么类型的解调，一个接收机所要执行的主要功能是滤波和放大。超外差式接收机就是这项工作的合理选择。
三、This section establishes the overall channel bandwidth selectivity and of adjacent the receiver.The bulk of the receiver’s gain will be concentrated here and some type of automatic gain control will be included to adjust for strength.The variations IFis in received usually signal at a lower frequency than the RF,but,in some higher special to cases,the reduce RFmay spurious be intermodulation anf image problems.
这个部分决定接收机的总体带宽和与之相连的通道选择问题。接收机模块的增益将主要集中在这一部分，为了适应接受信号强度的变化，某些形式的自动增益控制电路需要包括在其中。与射频相比，中频通常在一个较低的频率，但是，在一些特殊的情况中，中频可以高于射频以减少寄生地中间调制和镜像问题。 四、Signal are scalar-valued functions independent of variables.Often one or more for convenience,when the signals are one-dimensional,the variable “time.”The is independent independent referred variable to as may didcrete.Signals be continuous that are or continuous in both amplitude and time continuous-time (often referred or to analog as signals)are the most commonly encountered contexts.Discrete-time in signal signals processing are typically associated with sampling of digital continuous-time implementation of signal.Ina a signal processing system,quantization of signal required.Althogh amplitude not is precisely also correct in every context,discrete-time processing is often referred to signl as digital signal processing.
成的标量函数，通常为了方便， 信号是有一个或多个变量构当信号是一维时，独立变量被认为是周期的，独立变量可能是连续的或离散的，在信号处理环境下，信号在振幅和周期上的连续是常遇到的，离散时间信号是典型与连续时间信号抽样有关的信号，在数字的信号处理实现的系统中，要求信号的振幅是被量化，尽管在每一个环境中不精确地调整，离散时间信号处理通常被认为是数字信号处理。
五、Given a set of specifications,the filter design problem functional approximation to obtain becomes a problem in a discrete-time linear system whose winin frequency the response presceibed falls tolerances.IIR system imply approximation function of z ,while by FIR a ratonal system imply polynomial approximation .There are a variety of design techniques for both types of filters ,ranging from closed-form involve only substitution of design procedures,which specifications into design formulas,to techniques,where,for example algorithmic ,a solution may be obtained by an iterative procedure.
给定一组规定的参数，滤波器设计问题便成为获得一个频率响应在指定容限内的离散时间线性系统的逼近问题。信息检索系统意味着合理的z的函数近似,在冷杉系统意味着多项式近似。有多种设计技术这两种类型的过滤器,从封闭的过程,只涉及替代设计规范的设计公式,算法技术,,例如,一个解决方案可能是通过一个迭代的过程。
六、If the signal and noise spectra overlap,as is the typical case in practice,the above conditions connot simultaneously.In be such cases,we satisfied must compromise between the two design conditions and trade off one for the other.Depending on the application,we may decide to design remove the as filter much to the noise offer to as possible ,but at the expense of distorting signal.Alternatively,we may decide the desired to leave the desired signal as undistorted expense of as having possible,but some noise at the in the output.
如果信号和噪声谱重叠,在实践中是典型的案例,同时不能满足上述条件。在这种情况下,我们必须妥协之间的两个设计条件和贸易的其他。根据应用程序,我们可以决定设计提供的过滤器去除尽可能多的噪音,但以牺牲扭曲所需的信号。或者,我们可以决定离开期望信号尽可能不失真,但以牺牲一些噪声输出。
七、Image enhancement and restoration techniques are designed to impove the quality of an image as perceived by a human.In recent years enhancement has come to describe work well those as judged techniques by human that observers even though the mathematical completely criteria understood.For are not example rectification of a geometrically produces an obvious improvement distorted image in quality to a human observer.No objective improvement measure has of this yet quality been discovered.Image restoration is applied known distortion to the restoration for which of an a objective criterion can be applied. 图像增强和恢复技术是为了提高图像的质量是被一个人类。近年来增强来描述这些技术工作以及根据观察者即使数学标准不是完全理解。例如整流的几何失真图像质量产生明显改善人类观察者。客观测量的质量改进尚未发现。图像恢复是应用客观准则恢复一个已知失真的图像。
八、The word telecommunications is used to describe communication at a distance which involve some form conversation of over equipment.Thus,a a telephone system is certainly a telecommunication people shouting at whereas each other two is not.For a telephone conversation the is telecommunication both mechanical equipment and electrical.Although this is true of most of the systems which we will consider,it is certainly not a prerequisite for a telecommunications instance a conversation system.For using a voice tube,i.e.,an acoustic system,would telecommunication.For most of the also be classed as a section we will concentrate on electrical systems.
“电信”这个词是用来描述通信距离涉及某种形式的设备。因此,谈话在电话系统当然是一个电信而不是两个人对对方。电话交谈的电信设备是机电。虽然这是真实的大多数系统,我们将考虑,这当然不是一个电信系统的先决条件。例如使用话筒的对话,也就是说。,一个音响系统,也被列为电信。对于大多数的部分我们将专注于电力系统。
九、Radio transmission channel use radio wave propagation between antennae at the transmitter transmitter and uses receiver.The a modulation radio process to produce a radio frequency(RF)signal,i.e.,to
convent the message signal into a form which is suitable for transmission transmitter will . Normally also need the to contain an amplifier to ensure that the strong enough when it reaches the transmitted signal will be receiver.
无线电传输通道使用无线电波天线在发射机和接收机之间的传
播。无线电广播发射机使用调制过程产生射频(RF)信号,即,修道院消息信号转化成适合传播。通常传感器还需要包含一个放大器确保信号传输时将足够强大到达接收器。
十、For many years there have been economic attempts potentialities to realize of time the division multiplexing. It is by no means a new concept and was used in telegraphy before telephony before telephony came on the scene. simply synchronized The devices commutators used were where “sampled” one each at the of a sending number end of individual channels in sequence and transmitted the samples in sequence. receiving end received the samples The other device at the and distributed them in the correct sequence individual to channels. the corresponding Obviously there was a problem of maintaining synchronism. the This commutators problem in remains but modern electronic methods reliable have provided ways of achieving cheap and the required result.
多年来人们尝试实现时分多址的经济潜力。这就意味着有一个新概念，电话的实现在电报使用之前的。所应用的设备只是同步交换机，在发送端顺序地对每一个通道采样，并顺序地将这些采样值发送出去。另一些接收端的设备接收采样值，并对每个通信信道的采样值按照正确的顺序分配。显然在同步交换机的维护方面有问题。这个问题是现代网络已经提供廉价的、可靠的方式来获得需要的结果。
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