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Science and technology
科学技术
Low-cost radar
低成本雷达
A programme worth watching
值得一看的节目
How air-traffic control can use television signals to plot aircraft
空中交通管制局如何利用电视信号找出飞行器位置？
A NOVEL radar will soon be helping to keep an eye on aircraft flying over London.
很快，一种新式雷达将帮忙监视伦敦上空的飞机。
Conventional radar uses a rotating antenna to sweep the sky, sending out radio pulses and detecting those which are reflected back from aircraft.
传统雷达使用旋转天线扫视上空，不断发出射电脉冲并探测被飞行器反射回来的部分。
The experimental system that will begin operation in June does not send out any signals of its own,
而将于6月份启动的实验系统并不会自己发出任何信号，
but instead relies on a network of receivers to pick up television programmes.
而是依靠一个接受电视信号的接收器网络。
It is hard to imagine British TV staples like Cash in the Attic, Downton Abbey and endless repeats of Top Gear being used to detect aircraft.
很难想象像《家中藏宝》、《唐顿庄园》、《疯狂汽车秀》等这类英国的主打电视节目被用来侦查飞行器。
But that, in effect, is what will be happening.
但事实就将会如此。
By measuring the slight differences between the original broadcast signal and the signals reflected from aircraft flying in the vicinity, it is possible to plot the position of aircraft on a screen, just as is done with conventional radar.
通过测量原广播信号和附近飞行器反射信号间的细微差别，有可能在屏幕上标绘出飞行器的位置，这和传统雷达的工作原理一样。
The difference is that a system that relies on signals already in the air can be simpler, cheaper and use a lot less power.
两者的区别是，利用空中已有信号的操作系统可以更简便、更便宜，还能省不少电。
The London trial is being run by Thales UK, an engineering group, Roke Manor Research, an RD consultancy, and NATS, which manages Britain's air-traffic control.
伦敦实验系统的运行由工程组泰利斯英国公司、研发咨询公司曼乐研究公司和英国国家空运局负责，
It is backed by the British government's Technology Strategy Board.
并得到了英国政府技术战略委员会的支持。
The group call their system multi-static primary surveillance radar.
工程组把自己的系统称为多基站主监视雷达，
It is a form of passive radar, which goes back a long time.
属于存在已久的被动雷达中的一种。
Although it had been known since the late 19th century that radio waves can be reflected by objects, it was not until the years leading up to the second world war that a number of countries began secretly developing ways to detect aircraft.
虽然19末世纪时人们就已经知道物体能够反射无线电波，但直到二战前几年才有一些国家开始秘密研究侦查飞机的方法。
Many of the early tests relied on ordinary broadcasts to provide the signals.
这些早期的测试当中有很多都靠普通的无线电波来提供信号。
In an experiment in 1935 a Handley Page Heyford bomber flew between a receiving station and a BBC transmission tower to see how well it could be detected.
在1935年的一场实验当中，一个名为亨得利·佩奇·海福德飞行员驾驶轰炸机从BBC发射塔和一个接收站之间飞过，从而找出飞机能在多大程度上被侦查出来。
Well enough, it seems, because the Air Ministry immediately ordered a full demonstration system.
看来当时的效果还不错，因为航空部马上下达命令要求进行全套演示。
Blip, blip
雷达界的新老交替
In 1940 the US Navy coined the term radar to describe radio detection and ranging.
1940年，美国海军创造出雷达一词，用以描述无线电探测和测距。
Modern radar is highly sophisticated but it largely relies on emitting a signal.
现代雷达极其复杂，但主要还是靠自己发出信号。
By measuring the time taken for the reflected signal to return it is possible to work out the position of an aircraft.
通过测量被反射信号返回雷达所需的时间，就有可能计算出飞行器的位置。
A slight shift in the frequency, because of the Doppler effect, means its speed and direction can be measured too.
由于多普勒效应，返回信号的频率有微小变化，这就意味着飞行器的速度和飞行方向也可以被测量出来。
Passive radar can take similar measurements and is already used in limited ways, mostly by the armed forces.
被动雷达可以进行类似的测量，并且已经得到一些受限应用。
Relying on background signals to detect objects has an advantage in stealth operations:
在秘密行动中依靠背景信号来侦查物体有这样一个优势:
no pulse is sent out to alert anyone to what you are doing, or attract an anti-radar missile.
由于没有发出脉冲信号，没人会警觉你在什么，也不会引来反雷达导弹。
The growth in radio and television broadcasts—especially with digital and high-definition TV—now provides an enormous amount of high-frequency radio waves which are ideally suitable for passive radar systems.
现在无线电和电视广播的增长提供了海量的高频电波，这些非常适合用于被动雷达系统。
Moreover, the availability of cheap and powerful computing makes it feasible to analyse the data required to build a system like MSPSR.
此外，成本低廉和功能强大的计算机可以分析需要用于建立类似MSPSR系统的数据。
Thales and its partners expect to be able to produce results as good as conventional radar.
泰利斯工程组和合伙人们期待MSPSR的表现能和传统雷达一样好。
The trials are designed to see how passive radar could support Britain's air-traffic management.
实验项目的目的在于找出被动雷达能够如何帮助管理英国的空中交通。
It could help small airports that lack radar or fill gaps in areas where coverage is currently patchy.
它有助于那些缺乏雷达的小型机场，或者弥补那些雷达覆盖不完整地区的缺陷，
MSPSR might also reduce the interference caused in some places by wind turbines.
MSPSR还能减少一些地方由涡轮机造成的干扰，
And because it is a networked system it could be more reliable than the present set-up, which typically depends on using just one radar at each airport.
它是一个呈网络覆盖的系统，比目前的系统更可靠。
The aviation industry is cautious about adopting new technologies wholesale, so there is a long way to go before conventional radar is turned off in favour of passive systems.
航空业在大规模采用新技术方面很是谨慎，因此传统雷达完全让位于被动雷达还尚有时日。
But governments may be tempted to think about doing so, for reasons that go beyond passive radar's lower operating costs.
但政府或许会对此动心，原因不只是被动雷达的成本更加低廉：
With growing demand for wireless devices, passive radar would allow the radio spectrum currently used by conventional radar to be freed up and auctioned off to mobile operators.
随着无线设备的需求不断增加，被动雷达能够将目前用于传统雷达的无线电频谱解放出来，然后再拍卖给移动运营商。
One difficulty is that passive radar relies on a third party for its signals.
被动雷达的一个难题在于它要依靠第三方提供的信号。
The continued availability of transmissions is considered to be part of Britain's critical national infrastructure, says John Smith, the project leader for Thales.
泰利斯工程组的项目带头人约翰?史密斯说，广播电视业被认为是英国关键的国家基础设施。
Nevertheless, he adds, the study will look at how agreements can be made with broadcasters to ensure reliability and performance, and how to deal with routine maintenance when TV transmission towers are turned off.
不过他补充道，研究将着眼于如何跟广播公司达成协议，以及如何在电视信号发射中断时进行例行维护。
Air-traffic controllers and pilots would not take kindly to being confronted with the equivalent of a TV test card.
空中交通管制员和飞行员可不会乐意接受电视测试卡的等价物。
