1、Unit Basic Knowledge of Electronics Lesson 4 Radio Waves New Words (24) electromagnetic i,lektrumnetik a. 电磁的 wavelength weivle n. 波长 fundamental ,fndmentl a. 基础的， 基本的 medium midim n. 介质，传导体 aerial ril n. 天线 curvature k:vt n. 弯曲, 曲率 ionosphere ain,sfi n. 电离层 moleculemlikjul n. 分子 ultraviolet,ltrvail
2、t a. & n. 紫外(线) 的，紫外线辐射 radiation ,reidiein n. 辐射, 放射, 放射线, 放 射物 refractrifrkt vt. (使)折射, 测定.的折射度 earthwards :wdz a. 向地的 attenuate tenjueit v. 削弱 reflection reflekn n. 反射；映象 intervention ,intvenn n. 干涉 intervene ,intvi:n n. & vi. 干涉, 干预, 介入; 干涉 obstacles bstkl n. 障碍 corresponding ,k:rispndi a.符合的; 一
3、致的;相同的 astronomical ,strnmikl a. 天文的， 天文学的 resonator rezneit n. 谐振器 broadcasting br:d,k:sti n. 广播 navigation ,nviein n. 航海 antenna nten n. 天线 resonate rezneit v. 调谐Phrases and Expressions at the speed of 以的速度Notes1. They are energy-carriers which travel at the speed of light v, their frequency f and
4、 wavelength being related, as for any wave motion, 它们携带能量且以光速在空气中传播，它们的频率与波长相关，即任何电磁波传播时， (1) which引出定语从句，修饰energy-carriers；(2) at the speed of：“以的速度”如：He is driving the car at the speed of 100 km an hour. (3)their frequency f and wavelength being related是现在分词的独立结构，充当状语。2. The smal1er is, the larger
5、 f. 波长 越小，频率f越高。 重要句型the more the more ，表示“越 越 ”，如文中另一句the higher the frequency the greater the absorption（频率越高，能量被吸收得越多）。3. Radio waves can be described either by their frequency or their wavelength. 无线电波既能用频率又能用波长来描述。 句型either or ，或者 或者 , 如：Either he can stay home or go to the movies.4. But the fo
6、rmer is more fundamental since, unlike (and v), f does not change when the waves travel from one medium to another. 但前者更常用，因为频率不象速度，不会因传播媒介的改变而变化。 (1) the former指their frequency；(2) when the waves travel from one medium to another是时间状语从句。5. This travels along a ground, following the curvature of the
7、 earths surface. 这种波按地球表面的曲度，沿地表面传播。 句中following the curvature of the earths surface是现在分词短语，充当状语。6. This consists of layers of air molecules (the D, E and F layers), stretching from to 500 kms, which by the suns ultraviolet radiation. 电离层由空气分子层组成（包括D、E、F层），位于地球上方80公里到500公里处，它由于太阳紫外线的辐射而失去电子，因而带正电荷。
8、(1) This指前句中的ionosphere（电离层）； (2) stretching from to 500 kms是现在分词短语，充当定语，修饰layers of air molecules；(3)which by the suns ultraviolet radiation是非限制性定语从句，修饰air molecules。7. On striking the earth the sky wave bounces back to the ionosphere where it is again gradually refracted and returned earthwards as
9、 if by reflection. 反射回地面的天波又从地面反射回电离层，并再次被反射回地面，如“影像”一样。 (1) where引导定语从句，修饰ionosphere；(2) 由as if 引出的从句as if by reflection用虚拟语气，省略了谓语部分were refracted。Translation of TextsLesson 4 Radio Waves Radio waves are a member of the electromagnetic family of waves. They are energy-carriers which travel at the
10、speed of light（v）, their frequency（f） and wavelength（）being related, as for any wave motion, by the equation v = f where v = c = 3.0 108m/s in a vacuum (or air). If = 300 m, then f= v/ = 3.0 l08/(3.0 102) = 106 Hz= l MHz. The smal1er is, the larger f. 第第4课课 无线电波无线电波 无线电波是电磁波大家族中的一员，它们携带能量且以光速在空气中传播，
11、它们的频率与波长相关，即任何电磁波传播时，有 v = f 这里，v = c = 3.0 108m/s（在空气中），如果 = 300 m，则f= v/ = 3.0 l08/(3.0 102) = 106 Hz= l MHz。波长越小，频率f越高。 Radio waves can be described either by their frequency or their wavelength. but the former is more fundamental since, unlike (and v), f does not change when the waves travel fro
12、m one medium to another. 无线电波既能用频率又能用波长来描述。但前者更常用，因为频率不同于速度，它不会因传播媒介的改变而变化。 Radio waves can travel from a transmitting aerial in one or more of three different ways (as shown in Fig.4-1). 从天线辐射出去的无线电波通常以三种形式传播（如图41所示）。 (a) Surface or ground wave. This travels along a ground, following the curvature
13、of the earths surface. Its range is limited mainly by the extent to which energy is absorbed from it by the ground. Poor conductors such as sand absorb more strongly that water, and the higher the frequency the greater the absorption. The range may be about 1,500 km at low frequencies (long wave，but
14、 much less for v.h.f). （a）地表波或地波 这种波按地球表面的曲度，沿地表面传播。它的传播范围有限，其能量被地表面吸收，恶劣的地形条件如沙漠比水面更易吸收能量，频率越高，能量被吸收得越多。低频波（长波）的传播范围约为1500公里。高频波的传播范围要小得多。 (b) Sky wave. This travels skywards and, if it is below a certain critical frequency (typically 30MHz), is returned to earth by the ionosphere. This consists of
15、 layers of air molecules (the D, E and F layers), stretching from about 80 km above the earth to 500 km, which have become positively charged through the removal of electrons by the suns ultraviolet radiation. On striking the earth the sky wave bounces back to the ionosphere where it is again gradua
16、lly refracted and returned earthwards as if by reflection. This continues until it is completely attenuated. （b）天波 沿天空传播，若低于某个关键频率（如30MHz），会被电离层反射回地面。电离层由空气分子层组成（包括D、E、F层），位于地球上方80公里到500公里处，它由于太阳紫外线的辐射而失去电子，因而带正电荷。反射回地面的天波又从地面反射回电离层，并再次被反射回地面，如此反复多次直到能量完全衰减。 (c) Space wave. For v. h. f., u.h.f. and
17、microwave signals, only the space wave, giving line-of-sight transmission, is effective. A range of up to 150km is possible on earth if the transmitting aerial is on high ground and there are no intervening obstacles such as hills, buildings or trees. （c）空间波 甚高频、超高频和微波只能以空间波的形式才能有效传播，空间波也称视距传播。如果天线架
18、设很高且没有障碍阻隔，如高山、建筑物、大树等，空间波的传播距离可达150公里。 Radio waves have frequencies from 300 GHz to as low as 3 Hz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are made by lightning, or b
19、y astronomical objects. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications (as shown in Fig.4-2). 无线电波频率从300兆赫到3 赫兹，相应的波长从1毫米到100公里。像其他所有
20、的电磁波一样，它们以光速传播。自然产生的无线电波是由闪电或天体形成。人工产生的无线电波用于固定和移动无线电通讯，广播，雷达和其他导航系统以及卫星通信，计算机网络及无数其他应用（如图42所示）。 In order to receive radio signals, for instance from AM/FM radio stations, a radio antenna must be used. However, since the antenna will pick up thousands of radio signals at a time, a radio tuner is nec
21、essary to tune in to a particular frequency (or frequency range). This is typically done via a resonator (in its simplest form, a circuit with a capacitor and an inductor). The resonator is configured to resonate at a particular frequency (or frequency band), thus amplifying sine waves at that radio
22、 frequency, while ignoring other sine waves. Usually, either the inductor or the capacitor of the resonator is adjustable, allowing the user to change the frequency at which it resonates. 为接收无线电信号，例如从调幅/调频广播电台接收信号，必须使用无线天线。然而，由于天线可以同时接收数以千计的广播信号，必须有一个无线电调谐器调整到一个特定的频率（或频率范围）。这通常是通过谐振器实现的（其最简单的形式是一个由电
23、容和电感组成的电路）。谐振器被设置在某个特殊频率（或频段），从而放大那个具有特殊频率的正弦波，而忽略其他无线电波。通常，谐振器的电感或电容都是可调的，允许用户对谐振器改变频率进行调谐。Exercises1.Write T (True) or F (False) beside the following statements about the text.a. Radio waves are energy-carriers which travel at the speed of light (v), their frequency (f) and wavelength ().b. Radio
24、waves can be described by their frequency rather than wavelength.c. The frequency of the radio waves is more fundamental than wavelength since, unlike (and v), f does not change when the waves travel from one medium to another. d. Radio waves can travel from a transmitting aerial in one or more of t
25、hree different ways.e. Its range is no limited by the extent to which the ground absorbs energy from it.f. Poor conductors such as sand absorb more strongly than water, and the higher the frequency the greater the absorption.2.Match the following terms to appropriate definition or expression.a. Radi
26、o waves 1. sand b. Surface or ground wave 2. the wave travels along a ground, following the curvature of the earths surfacec. Sky wave 3. the wave giving line-of-sight transmissiond. Space wave 4. the wave travels skywards ,if below a certain critical frequency is returned to earth e. Poor conductor
27、s 5. a member of the electromagnetic family of waves 3.Fill in the missing words according to the text.a. In a vacuum (or air)，if = 300 m, then f=v/=_= 106 Hz= l MHz. The smaller is, the larger f. b. The range may be about _km at low frequencies ( long wave; but much less for v.h.f ).c. This consist
28、s of layers of air molecules (the D, E and F layers), stretching from about _ km above the earth to _ km, which have become positively charged through the removal of electrons by the suns ultraviolet radiation.d. A range of up to 150kms is possible on earth if the _ is on high ground and there are n
29、o intervening obstacles such as hills, buildings or trees.4. Translate the following paragraphs into Chinese. (a) Surface or ground wave. This travels along a ground, following the curvature of the earths surface. Its range is limited mainly by the extent to which the ground absorbs energy from it.
30、Poor conductors such as sand absorb more strongly than water, and the higher the frequency the greater the absorption. The range may be about 1,500 km at low frequencies ( long wave; but much less for v.h.f ). (b) Sky wave. This travels skywards and, if it is below a certain critical frequency (typi
31、cally 30MHz), is returned to earth by the ionosphere. This consists of layers of air molecules (the D, E and F layers), stretching from about 80 km above the earth to 500 km, which have become positively charged through the removal of electrons by the suns ultraviolet radiation. On striking the eart
32、h the sky wave bounces back to the ionosphere where it is again gradually refracted and returned earthwards as if by reflection. This continues until it is completely attenuated. (c) Space wave. For v. h. f., u.h.f. and microwave signals, only the space wave, giving line-of-sight transmission, is effective. A range of up to 150kms is possible on earth if the transmitting aerial is on high ground and there are no intervening obstacles such as hills, buildings or trees.End
