创新学分英文翻译

姓名：杨震学号：200804135047
英语文章的翻译：
Introduction to Electronic Communications
1.Historical perspective
The fundamental purpose of an electronic communications is to transfer information from one place to another. Thus , electronic communication can be summarized as the transmission , reception , and processing of information between two or more locations using electronic circuits . The original source information can be in analog (continuous) form , such as the human voice or music ,or in digital(discrete) form , such as binary-coded numbers or alphanumeric codes . All forms of information , however , must be converted to electromagnetic energy before being propagated through an electronic communications system .
Samuel Morse developed the first electronic communications system in 1837 . Morse used electromagnetic induction to transfer information in the form of dots , dashes , and spaces between a simple transmitter and receiver using a transmission line consisting of a length of metallic wire . He called his invention the telegraph . In 1876 Alexander Graham Bell and Thomas A . Watson were the first successfully transfer human conversation over a crude metallic were communications system , they called the telephone .
Guglielmo Marconi successfully transmitted the first wireless radio signals through Earth's atmosphere in 1894 , and in 1908 Lee Deforest invented the triode vacuum tube which provided the first practical means of amplifying electrical signals . Commercial radio began in 1920 when radio stations began broadcasting amplitude-modulated(AM) signals , and in 1933 , Major Edwin Howard Armstrong invented frequency modulation(FM) . Commercial broadcasting of FM began in 1936 .
Although the fundamental concepts and principles of electronic communications have changed little since their inception , the methods and circuits used to implement them have undergone considerable change . In recent years , transistors and linear integrated circuits have simplified the design of electronic communications circuits , thus allowing for miniaturization , improved performance and reliability , and reduced overall costs . In recent years , there has been an overwhelming need for more and more people to communicate with each other . This tremendous need has stimulate a monumental growth in the electronic communications industry . Modern electronic communications systems include metallic cable systems , microwave and satellite radio systems , and optical fiber systems .
A time chart showing the historical development of communications is given in Table 6.1 . The reader is encouraged to spend some time studying this table to obtain appreciation for the chronology of communications . Note that although the telephone was developed late in the nineteenth century , the first transatlantic telephone cable was not completed until 1954 . Previous to this date , transatlantic calls were handled via shortwave radio . Similarly , although the British began television broadcasting in 1936 , transatlantic television relay was not possible until 1962 when the Telstar I satellite was placed into orbit . Digital transmission system embodied by telegraph systems --were developed in the 1850s before analog systems --in the twentieth century .
2.Electronic Communications Systems
Communications Systems may be described by the block diagram shown in Figure 6.1. Regardless of the particular application , all communications systems involve three main subsystems : the transmitter , the channel , and the receiver . The message from the source is represented by the information input waveform m(t) . The message delivered to the sink is denoted
by )(~t m . The "~" indicates that the message received may not be the same as that transmitted . That message information may be in analog or digital form , depending on the particular system , and it may represent audio , video , or some other type information . In multiplexed systems , there may be multiple input and output message sources and sinks . The spectra(or frequencies) of m(t)
and )(~t m are concentrated about f=0 ; consequently , they are said to be baseband signals .
The signal-processing block at the transmitter conditions the source for more efficient transmission . For example , in an analog system , the signal processor may be an analog low-pass filter that is used to restrict the bandwidth of m(t) . In a hybrid system , the signal processor may be an analog-to-digital converter(ADC) . This produce a "digital word" that represents samples of the analog input signal . In this case , the ADC in the signal processor is providing source coding of the input signal . In addition , the signal processor may also add parity bits to the digital word to provide channel coding so that error detection can be used by the signal processor in the receiver to reduce or eliminate bit errors that are caused by noise in the channel . The signal at the output of the transmitter signal processor is a baseband signal because it has concentrated near f=0 .
The transmitter carrier circuit converts the processed baseband signal into a frequency band that is appropriate for the transmission medium of the channel . For example , if the channel consists of a fiber optic cable , the carrier circuits convert the baseband input to light frequencies , and the transmitted signal s(t) is light . If the channel propagates baseband signals , no carrier circuits are needed , and s(t) can be output of the processing circuit at the transmitter . Carrier circuits are needed when the transmission channel is located in a band of frequencies around c f >>0 . In this case , s(t) is said to be a band-pass because it is designed to have frequencies located in a band about c f . For example , an amplitude modulated(AM) broadcasting station
with an assigned frequency of 850kHz has a carrier frequency of
c f =850kHz . The mapping of the baseban
d input information waveform m(t) into th
e band-pass signal s(t) is called modulation .
翻译：
电子通信简介
1.历史回顾
电子通信系统的基本作用是把信息从此地传送到彼地。

因此，电子通信就是利用电路在两地或多地之间进行信息的发送、接收和处理。

原始的信息源既可以是模拟（连续）的，例如语音或音乐；也可以是数字（离散）的，例如二进制编码数或字符。

然而在通过电子通信系统传输之前，各种信息都须先转换成电磁能量。

Samuel Morse 于1837年发明了第一个电子通信系统。

Morse 利用电磁感应来传送用点、破折号、空格表示信息，简易的发送机与接收机之间用金属传输线连接。

他把他的发明称为电报。

1876年，Alexander Graham Bell 和 Thomas A. Watson 利用一个简陋的金属线通信系统成功地传送了人的对话，他们把这个系统称为电话。

Guglielmo Marconi 于1894年首次成功地通过大气层发送了无线电信号。

Lee de Forest 于1908年发明了真空三极管，为放大电信号提供了第一个实用手段。

商用广播始于1920年，当时采用的是调幅（AM ）信号。

1933年， Edwin Howard Armstrong 发明了频率调制（FM ），而商用调频广播始于1936年。

尽管电子通信的基本概念和原理自开创以来并没有多大变化，但实现的方法和电路已有飞速发展。

近年来，晶体管和线性集成电路已大大简化了电信通信电路的设计，并使其小型化，提高了性能和可靠性，降低了成本。

近来，越来越多的人对通信的强烈需求，刺激了通信业的强烈需求，刺激了通信业空前迅猛的发展。

现代通信系统已涵盖了电缆系统、微波系统、卫星系统和光纤系统。

通信发展的历史纪年表列于表6.1中。

建议读者学习此表，以掌握通信的发展历程。

值得注意的是，尽管电话早在19世纪后期就开发成功，但直到1954年，穿越大西洋的电话电缆才敷设完成。

而在此之前，越洋电话只能通过短波无线电台进行。

类似地，尽管英国早在1936年就开始了电视广播，但直到1962年Telstar I 卫星送入轨道后，越洋电视转播才成为可能。

以电报为代表的数字传输系统研发于19世纪50年代，早于以电话为代表的模拟系统，它是20世界才开发的。

2. 电系通信系统
通信系统可以用图6.1所示的方框图来描述。

无论何种具体应用，通信系统都包括三个主要的子系统：发送机、信道和接收机。

从信源来的消息表示为输入信息波形m(t)，此消息传送到终端后用)(~
t m 表示。

符号“~”表明收到的消息与发送的消息不完全相同。

这就是说，终端的信息)(~t m 可能收到信道噪声的污染，或者是系统有失真，例如不希望的滤波或非线
性。

取决于实际的系统，消息可能是浓密的或数字的，可能表示声音、图像或其他类型的信
息。

在多路系统中，有多个输入信源和输出终端。

m(t)和)(~t m 的频谱集中在零频(f=0)附近，
因此常称为基带信号。

发送机中的信号处理单元对信源进行调理，以便更有效地传送。

譬如说，在模拟系统中，信号处理器可以是一个模拟低通滤波器，以限制m(t)的带宽。

在混合系统中，信号处理器可以是一个模-数变换器（ADC ），它用数字来表示模拟输入信号的样本值。

也就是说，ADC 对输入信号进行源编码。

此外，信号处理器还可以给数码字加入奇偶校验位，即提供信道编码，似的接收机的信号处理器可以进行五码检测和纠错，以减少或消除由信道噪声所引起的误码。

发送机中信号处理器的输出信号仍是基带信号，因为它的频谱也集中在f=0附近。

发送机中的载波电路把处理后的基带信号变换到适于在信道媒体中传输的频带。

例如，假设信道是光纤，那么载波电路就把基带信号，那就不需要载波电路，s(t)也就是信号处理器的输出信号。

当传输信号的频带在
c f >>0附近时，载波电路是必需的。

此时，s(t)是带通信号，因为他的频率已集中在c f 附近。

例如，850kHz 的广播电台的调幅信号的载频c f =850kHz 。

把基带的输入信息波形m(t)变换到通带信号s(t)的过程成为调制。