中職電子專業(yè)英語第13章教學(xué)課件

1、正版可修改PPT課件(中職）電子專業(yè)英語第13章教學(xué)課件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下一頁返回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上一頁下一頁返回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上一頁下一頁返回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. 改變，變更，使多樣化parameter n. 參數(shù)，參量modulate v. 調(diào)整，調(diào)節(jié)，調(diào)制modulation n. 調(diào)制whereby adv. 靠那個(gè)，憑那個(gè)，借以instantaneous adj. 即時(shí)的，瞬間的constant adj. 不變的，恒定的，穩(wěn)定的Unit 13 Modulation上一頁下一頁返回amplitude n. 振幅extracting n. 萃取，提取，提煉detection n. 偵察

10、，探測，檢波demodulation n. 解調(diào)，檢波exclusively adv. 排外的，專有地deviation n. 偏向，偏差inaccordance with 按照或依據(jù)某事物proportional to （與某事物大小 、數(shù)量或程度上）相稱的，成比例的in other words 換句話說；也就是說Unit 13 Modulation上一頁下一頁返回Phrases and expressionscarrier wave 載波first wave基波modulating wave 調(diào)制波 /modulated wave 已調(diào)波amplitude modulation (AM)

11、振幅調(diào)制frequency and phase modulation (FM and PM) 頻率和相位調(diào)制modulating signal 調(diào)制信號(hào)frequency deviation 頻率偏移Unit 13 Modulation上一頁下一頁返回Notes1. according to意為“根據(jù)”。2. by means of “通過方式，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上一頁下一頁返回【 】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上一頁下一頁返回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