中职电子专业英语第13章教学课件

1、正版可修改PPT课件(中职）电子专业英语第13章教学课件Warming-upI.Can you point out the name of the following picture?II.Do you know what the following abbreviations or symbols stand for?AM FMPMIII.Talk about Modulation in English. And the following patterns you can use: What is the first wave?What is the second wave?Could y

2、ou tell us something about AM, FM and PM ?Unit 13 Modulation下一页返回Text Comprehension Modulation In order to send a message by means of radio waves, it is necessary to vary some parameter of these waves according to the information to be transmitted. This can be obtained by means of modulation. Modula

3、tion is the process whereby one or more characteristics of a wave are varied with a function of the instantaneous value of another wave. The first wave, usually a single frequency wave of constant amplitude, is known as the carrier wave and the second as the modulating wave. The process of extractin

4、g the single information from a modulated carrier wave is called detection or demodulation. Unit 13 Modulation上一页下一页返回Initially, amplitude modulation was used exclusively for communications and broadcasting. Later, with the widespread adoption of higher radio frequencies (3000 kilohertz300 megahertz

5、) for communications and broadcasting, frequency and phase modulation techniques came into increasing use. These are often referred to as FM and PM respectively.In amplitude modulation, the instantaneous amplitude of the carrier is varied in proportion to the modulating signal. In frequency modulati

6、on, the instantaneous frequency of the carrier varied in accordance with the signal to be modulated on the wave. While the amplitude of the carrier frequency wave is constant. In phase modulation, the value of the phase angle of the sinewave carrier is varied so that its magnitude is proportional to

7、 the instantaneous amplitude of the modulating signal. It must be noted that there is an instantaneous frequency change or deviation during the time that the phase is shifted when the phase of the current in a circuit is changed. Unit 13 Modulation上一页下一页返回The frequency deviation in phase modulation

8、is proportional to the amplitude of the modulating signal and its frequency. While in frequency modulation, the frequency deviation is proportional only to the amplitude of the modulating signal. In other words, the phase modulation is merely a way of obtaining a frequency modulated wave in which th

9、e frequency deviation is proportional to the modulating frequency.Vocabularyvary v. 改变，变更，使多样化parameter n. 参数，参量modulate v. 调整，调节，调制modulation n. 调制whereby adv. 靠那个，凭那个，借以instantaneous adj. 即时的，瞬间的constant adj. 不变的，恒定的，稳定的Unit 13 Modulation上一页下一页返回amplitude n. 振幅extracting n. 萃取，提取，提炼detection n. 侦察

10、，探测，检波demodulation n. 解调，检波exclusively adv. 排外的，专有地deviation n. 偏向，偏差inaccordance with 按照或依据某事物proportional to （与某事物大小 、数量或程度上）相称的，成比例的in other words 换句话说；也就是说Unit 13 Modulation上一页下一页返回Phrases and expressionscarrier wave 载波first wave基波modulating wave 调制波 /modulated wave 已调波amplitude modulation (AM)

11、振幅调制frequency and phase modulation (FM and PM) 频率和相位调制modulating signal 调制信号frequency deviation 频率偏移Unit 13 Modulation上一页下一页返回Notes1. according to意为“根据”。2. by means of “通过方式，以方式”。 I Choose the right answer from A, B, and C according to the text. 【 】1.The first wave is known as _.A. radio waveB. carr

12、ier wave C. single wave【 】2. The process of extracting the single information from a modulated carrier wave is called_.A. detectionB. first wave C. second wave【 】3. _ is necessary for transmitting information.A. ModulationB. Detection C. Demodulation.【 】4. _ was used exclusively for communication an

13、d broadcasting.A. AMB. DC.C. Not mentioned.Unit 13 Modulation上一页下一页返回【 】5. _ can vary some parameter of waves.A TransformerB ReceiverC ModulationII True or false.1. Modulation is necessary for transmitting information.2.The first wave usually a single frequency wave of constant amplitude is known as

14、 the modulating wave.3. The second wave is known as the carrier wave.4. Both AM and FM are used for broadcasting and communication today. 5. The phase modulation is merely a way of obtaining a frequency modulated wave.III Translate the following sentences.1. Modulation is the process whereby one or

15、more characteristics of a wave are varied with a function of the instantaneous value of another wave.Unit 13 Modulation上一页下一页返回2. The process of extracting the single information from a modulated carrier wave is called detection or demodulation.3. Initially, amplitude modulation was used exclusively for communications and broadcast-ing.4. In frequency modulation, the instantaneous frequency of the carrier varied in accordance with the signal to be modulated on the wave.5. It must be noted that