首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
Part Ⅱ Reading Comprehension (Skimming and Scanning) Directions: In this part, you will have 15 minutes to go over the passage q
Part Ⅱ Reading Comprehension (Skimming and Scanning) Directions: In this part, you will have 15 minutes to go over the passage q
admin
2013-01-22
55
问题
Part Ⅱ Reading Comprehension (Skimming and Scanning)
Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1. For questions 1-7, choose the best answer from the four choices marked A), B), C) and D). For questions 8-10, complete the sentences with the information given in the passage.
Satellite Ⅳ
Today, you see compact satellite dishes perched on rooftops all over the United States. Drive through rural areas beyond the reach of the cable companies and you’ll find dishes on just about every house. The major satellite television companies are bringing in more customers every day with the lure of movies, sporting events and news from around the world.
The Broadcast TV Problem
Conceptually, satellite television is, a lot like broadcast television. It’s a wireless system for delivering television programming directly to a viewer’s house. Both broadcast television and satellite stations transmit programming via a radio signal. Broadcast stations use a powerful antenna to transmit radio waves to the surrounding area. Viewers can pick up the signal with a much smaller antenna.
The main limitation of broadcast television is range. The radio signals used to broadcast television shoot out from the broadcast antenna in a straight line. In order to receive these signals, you have to be in the direct "line of sight" of the antenna. One problem is that the Earth is curved, so it eventually breaks the signal’s line of site. The other problem with broadcast television is that the signal is often distorted even in the viewing area. To get a perfectly clear signal like you find on cable, you have to be pretty close to the broadcast antenna without too many obstacles in the way.
The Satellite TV Solution
Satellite television solves the problems of range and distortion by transmitting broadcast signals from satellites orbiting the Earth. Since satellites are high in the sky, there are a lot more customers in the line of site. Satellite television systems transmit and receive radio signals using specialized antennas called satellite dishes.
The television satellites are all in geosynchronous orbit, meaning that they stay in one place in the sky relative to the Earth. Each satellite is launched into space at about 7,000 mph (11,000kph), reaching approximately 22,200 miles (35,700km) above the Earth. At this speed and altitude, the satellite will revolve around the planet once every 24 hours—the same period of time it takes the Earth to make one full rotation. In other words, the satellite keeps pace with our moving planet exactly. This way, you only have to direct the dish at the satellite once, and from then on it picks up the signal without adjustment, at least when everything works right.
The Overall System
Early satellite TV viewers were explorers of sorts. They used their expensive dishes to discover unique programming that wasn’t necessarily intended for mass audiences. The dish and receiving equipment gave viewers the tools to pick up foreign stations, live feeding between different broadcast stations, NASA activities and a lot of other stuff transmitted using satellites.
Some satellite owners still seek out this sort of programming on their own, but today, most satellite TV customers get their programming through a direct broadcast satellite (DBS) provider, such as Direct TV or the Dish Network. The provider selects programs and broadcasts them to subscribers as a set package. Basically, the provider’s goal is to bring dozens or even hundreds of channels to your television in a form that approximates the competition, cable TV. Unlike earlier programming, the provider’s broadcast is completely digital, which means it has much better picture and sound quality. Early satellite television was broadcast in C-band radio—radio in the 3.4-gigabertz (GHz) to 7-GHz frequency range. Digital broadcast satellite transmits programming in the Ku frequency range (12 GHz to 14 GHz ).
The Programming
Satellite TV providers get programming from two major sources: national turnaround channels (such as HBO, ESPN and CNN) and various local channels (NBC, CBS, ABC, PBS and Fox affiliates in a particular area). Most of the turnaround channels also provide programming for cable television, and the local channels typically broadcast their programming over the airwaves.
Turnaround channels usually have a distribution centre that beams their programming to a geostationary satellite. The broadcast centre uses large satellite dishes to pick up these analogs and digital signals from several sources.
The broadcast centre converts all of this programming into a high-quality, uncompressed digital stream. At this point, the stream contains a vast quantity of data—about 270 megabits per second (Mbps) for each channel. In order to transmit the signal from there, the broadcast centre has to compress it. Otherwise, it would be too big for the satellite to handle.
Compression, Encryption and Transmission
The two major providers in the United States use the MPEG-2 compressed video format—the same format used to store movies on DVDs. With MPEG-2 compression, the provider can reduce the 270-Mbps stream to about 5 or 10 Mbps (depending on the type of programming). This is the crucial step that has made DBS service a success. With digital compression, a typical satellite can transmit about 200 channels. Without digital compression, it can transmit about 30 channels.
At the broadcast centre, the high-quality digital stream of video goes through an MPEG-2 encoder, which converts the programming to MPEG-2 video of the correct size and format for the satellite receiver in your house.
After the video is compressed, the provider needs to encrypt it in order to keep people from accessing it for free. Encryption scrambles the digital data in such a way that it can only be decrypted (converted back into usable data) if the receiver has the correct decryption algorithm and security keys.
Once the signal is compressed and encrypted, the broadcast centre beams it directly to one of its satellites. The satellite picks up the signal with an onboard dish, amplifies the signal and uses another dish to beam the signal back to the Earth, where viewers can pick it up.
The Dish and the Receiver
A satellite dish is just a special kind of antenna designed to focus on a specific broadcast source. The standard dish consists of a parabolic (bowl-shaped) surface and a central feed horn. To transmit a signal, a controller sends it through the horn, and the dish focuses the signal into a relatively narrow beam.
The end component in the entire satellite TV system is the receiver. The receiver has four essential jobs:
It de-scrambles the encrypted signal. In order to unlock the signal, the receiver needs the proper decoder chip for that programming package.
It takes the digital MPEG-2 signal and converts it into an analog format that a standard television can recognize. In the United States, receivers convert the digital signal to the analog NTSC format. Some dish and receiver setups can also output an HDTV signal.
It extracts the individual channels from the larger satellite signal. When you change the channel on the receiver, it sends just the signal for that channel to your TV.
It keeps track of pay-per-view programs and periodically phones a computer at the provider’s headquarters to communicate billing information.
While digital broadcast satellite service is still lacking some of the basic features of conventional cable (the ability to easily split signals between different TVs and VCRs, for example), its high-quality picture, varied programming selection and extended service areas make it a good alternative for some. With the rise of digital cable, which also has improved picture quality and extended channel selection, the TV war is really heating up.
______receives satellite television signal and decodes it for the TV screen.
选项
A、The satellite dish
B、The provider
C、The receiver
D、The viewer
答案
C
解析
细节题。由题目中的decodes找到小标题The Dish and the Receiver下第二段最后一句及第三段The receiver has four essential jobs: It de-scrambles the encrypted signal. In order to unlock the signal, the receiver needs the proper decoder chip for that programming package. (接收器有四个作用,它接收加密的信
转载请注明原文地址:https://kaotiyun.com/show/3BI7777K
0
大学英语六级
相关试题推荐
Readingbecamedifficultfortheoldlady,sotheoptician______glasses.
Forthispart,youareallowed30minutestowriteashortessayentitledCareerorMarriage?.Youshouldwriteatleast150wor
Forthispart,youareallowed30minutestowriteashortessayentitledShouldRetirementAgeBeRaised?Youshouldwriteatl
Forthispart,youareallowed30minutestowriteashortessayonthetopicofShouldSchoolsOfferHandwritingLessons?.You
Inmostmessages,thereisanobviousmeaningthataliteralreadingofthewordsandsentencesreveals.Butthereisoftenanot
Inmostmessages,thereisanobviousmeaningthataliteralreadingofthewordsandsentencesreveals.Butthereisoftenanot
Inmostmessages,thereisanobviousmeaningthataliteralreadingofthewordsandsentencesreveals.Butthereisoftenanot
Inmostmessages,thereisanobviousmeaningthataliteralreadingofthewordsandsentencesreveals.Butthereisoftenanot
Inmostmessages,thereisanobviousmeaningthataliteralreadingofthewordsandsentencesreveals.Butthereisoftenanot
随机试题
用于浅层平板荷载试验沉降观测的仪器设备精度不应低于()。
土地总登记中,对登记公告结果有异议的,可以向()申请复查。
某油田2009年8月份销售情况如下:(1)开采原油8万吨,其中销售6万吨,用于自办油厂加工1万吨,加热修井耗用1万吨;(2)采用分期收款方式销售一批原油6万吨,合同规定,货款分两个月收取,本月收取60%,其余货款于9月30日前收取;采用
多维立体组织结构中,()组成产品事业委员会。
根据以下混合资料,回答问题。2008年A省粮食作物播种面积2499.94千公顷,比上年增长0.8%。糖蔗种植面积136.04千公顷,下降1.2%;油料种植面积323.87千公顷,增长4.3%;蔬菜种植面积1112.63千公顷,增长4.5%。2008年A
【2014年山东省属真题】下列表述中,不能体现环境对人身心发展的影响的是()。
固定资产清理是因磨损、遭受非常灾害和意外事故而丧失生产能力,或因陈旧过时,须淘汰更新的固定资产,所办理的鉴定、报废、核销资产、处理残值等多项工作的总称。根据上述定义,下列不符合固定资产清理的是:
下列关于权利和义务的关系的说法不正确的一项是()。
成功智力理论
自1945年以来,局部战争几乎不断,但是却未发生像第二次世界大战那样严重的世界战争。这是因为人们恐惧于世界大战的破坏力。下列哪项,如果正确,最能削弱上述结论?
最新回复
(
0
)