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1、第七单元Telecommunications enables people to send and receive personal messages across town, between countries, and to and from outer space. It also provides the key medium for news, data, information and entertainment.When a signal reaches its destination, the device on the receiving end converts the e
2、lectronic signal back into an understandable message, such as sound over a telephone, moving images on a television, or words and pictures on a computer screen. 电信使世界各地的人们得以互相联系，即刻获取信息，并从边远地区实施通信。电信通常涉及一个信息发送者和一个或多个接收者，他们通过电话系统等把信息从一地发送到另一地的技术相联系。电信设备将不同类型的信息，如声音和图像，转换成电子信号。然后，这些 信号就可以通过电话线或无线电波等媒介进
3、行发送。信号到达目的地后，接收端的设备将电子信号转换 回可以理解的信息，如电话中的声音、电视上的活动图像或计算机屏幕上的 文字和 图片。电信使人们能够在城镇不同地方、国家之间以及向外层空间和从外层空间发 送和接收个人信息。电信也为新闻、数据、信息和娱乐提供了关键的媒介。Telecommunications messages can be sent in a variety of ways and by a wide range of devices. The messages can be sent from one sender to a singlereceiver(point-to-po
4、int) or from one sender to many receivers (point-to-multipoint). Personal communications, such as a telephone conversation between two people or a facsimile (fax) message, usually involve point-to-point transmission. Point-to-multipoint telecommunications, often called broadcasts, provide the basis
5、for commercial radio and television programming. 电信信息可通过各种方式和设备发送。信息可由一个发送者发送给一个接收者(点对点)，或者由一个发送者发送给多个接收者(点对多点)。个人通信，如两个人之间的电话对话或传真信息，通常涉及点对点的传输。通常称为广播的点对多点电信传输，为商业无线电和电视节目播送提供了基础。Telecommunications begin with messages that are converted into electronic signals. The signals are then sent over a medi
6、um to a receiver, where they are decoded back into a form that the person receiving the message can understand. There are a variety of ways to create and decode signals, and many different ways totransmit signals.电信以信息转换为电子信号为开端。然后，这些信号通过媒介发送到接收机，并在那里解码，恢复为接收信息的人能够理解的形式。有各种方法可以生成并解译信号，也有许多不同方法可以传输 信
7、号。Devices such as the telegraph and telephone relay messages by creating modulated electrical impulses, or impulses that change in a systematic way. These impulses are then sent by wires, radio waves, or other media to a receiver that decodes the modulation.电报机与电话机等设备，通过生成调制电脉冲或以系统化方式变化的脉冲，来传递信息。接下来
8、，这些脉冲通过导线、无线电波或其他媒介发送给接收机，并由其进行解调。The telegraph, the earliest method of delivering telecommunications, works by converting the contacts (connections between two conductors that permit a flow of current) between a telegraph key and a metal conductor into electrical impulses.hese impulses are sent alo
9、ng a wire to a receiver, which converts the impulses into short and long bursts of sound or into dots and dashes on a simple printing device.电报机是最早的传递电信信息的方法，它通过将电报电键与金属导体之间的接触(使电流得以流动的两个导体之间的连接)转换成电脉冲而进行工作。这些脉冲沿着导线发送到接收机，而接收机则将这些脉冲转换成长与短的声音脉冲串，或者在简单的打印设备上打印出来的点与划。T Specific sequences of dots and da
10、shes represent letters of the alphabet. In the early days of the telegraph, these sequences were decoded by telegraph operators. In this way, telegraph operators could transmit and receive letters that spelled words. Later versions of the telegraph could decipher letters and numbers automatically. T
11、elegraphs have been largely replaced by other forms of telecommunications, such as fax machines and electronic mail (e-mail), but they are still used in some parts of the world to send messages.特定的点与划序列代表字母表中的字母。在早期的电报中，这些序列由电报机操作员进行解译。这样，电报机操作员就可以发送和接收可拼成词语的字母。后来的电报机能自动解译字母和数 字。电报机在很大程度上已被其他的电信形式所取
12、代，如传真机和电子邮件， 但在 世界有些地方，电报机仍然用来发送信息。Telegraphs, telephones, radio, and television all work by modifying electronic signals, making the signals imitate, or reproduce, the original message. This form of transmission is known as analog transmission. Computers and other types of electronic equipment, how
13、ever, transmit digital information.电报机、电话机、无线电和电视都是通过修改电子信号，使其模拟或再现原来的信息，来进行工作的。这种传输称为模拟传输。然而，计算机和其他类型的电子设备是传输数字信号的。数字技术将信息转换成电子形式。其方法首先是多次测量信息的不同特性，如语音的音高和阜县 日里。Digital technologies convert a message into electronic form first by measuring different qualities of the message, such as the pitch and v
14、olume of a voice, many times. These measurements are then encoded into multiple series of binary numbers, or 1s and 0s.数字技术将信息转换成电子的形式。其方法首先是多次测量信息的不同特性，如语音的音高和音量。然后，这些测量值被编译成多个系列的二进制数或1与0。Finally, digital technologies create and send electrical impulses that correspond to the series of 1s and 0s. D
15、igital information can be transmitted faster and more clearly than analog signals, because the electrical impulses only need to correspond to two digits and not to the full range of qualities that compose the original message, such as the pitch and volume of a human voice.最后，数字技术生成并发送与这些系列的1和0相对应的电脉
16、冲。与模拟信号比较起来，数字信息可以更快、更清晰地传输，因为电脉冲仅需与两个数字对应，而不是构成原信息的所有特性，如人的说话声的音高和音量。While digital transmissions can be sent over wires, cables or radio waves, they must be decoded by a digital receiver. New digital telephones and televisions are being developed to make telecommunications more efficient.数字传输可以通过导线、电缆或无线电波发送，但必须由数字接收机进行解译。新型数字电话和电视正在开发中，以提高电信的效率。Most personal computers communicate
