14. Ознакомьтесь с дополнительными словами и выражениями:

medium frequency — средняя частота

frequency divider —делитель частоты

picture transmission — телевидение, передача телевизионных изображений

to superimpose one image on another — накладывать изображения одно на другое

15. Ответьте на вопросы, используя информацию текста:

1. What are main reasons to blend data into a carrier signal? 2. Is this form of modulation is a very efficient way to send information? 3. Why is the power required relatively large? 4. Is it possible to demodulate the signal if the carrier isn’t used as a reference? 5. Why is it impossible to filter out the whole sideband? 6. How is the transmission with only one sideband called? 7. What is the reason to remove the remaining carrier signal from the AM signal? 8. Where is SSB used?

16. Вставьте пропущенные слова:

amplitude, transmit, bandwidth, frequency, tuning, envelope, carrier, modulate

1. Amplitude modulation (AM) is a method used … a signal. 2. In the case of an analog signal to be sent, the … of the radio wave is modulated to be directly proportional to the value of the analog signal at the time. 3. Amplitude modulation typically produces a modulated output signal that has twice … of the modulating signal. 4. The working principles of AM radio is as follows: a … wave introduces an alternating positive and negative electrical voltage in the receiving antenna. 5. An AM receiver is capable of picking up the radio waves … from a radio station and transforming them into audible signals suitable to the human ear. 6. Because the carrier … is significantly greater than the modulating frequency it is possible to use a capacitor to smooth or filter the waveform to remove the carrier. 7. Several stations may be transmitting different signals simultaneously, and therefore the AM receiver must be capable of focusing on the specific station of your choice ( this is referred to as “… ”). 8. The … , or boundary, of the amplitude modulated signal embeds the information bearing signal.

17. Заполните пропуски предлогами:

1. Signals … low carrier frequencies require very large antennas. 2. The length … the antenna has an inverse relationship with the transmission frequency. 3. The original sound can later be detected … a radio receiver. 4. Let’s take the example of a carrier … a frequency of 1 MHz which is modulated … a steady tone of 1 kHz. 5. One signal can interfere with another. 6. The information can be demodulated only by generating a wave … the receiver at the carrier frequency. 7. The problem is that the more of the sideband you filter … , the more distortion you get …the detected waveform.

18. Переведите следующие предложения на русский язык:

1. Amplitude modulation is the modulation method used in the AM radio broadcast band. 2. In this system the intensity, or amplitude, of the carrier wave varies in accordance with the modulating signal. 3. Amplitude modulation is not efficient in terms of its power usage. 4. If the modulated carrier is rectified and the carrier frequency filtered out, the modulating signal can be recovered. 5. Single-sideband signals are very efficient in their use of the frequency spectrum when compared to standard amplitude modulation (AM) signals. 6. If part of one sideband and all of the other remain, it is called vestigial sideband, used mostly with television broadcasting, which would otherwise take up an unacceptable amount of bandwidth. 7. Nowadays, amplitude modulation is used for audio broadcasting on the long, medium and short wave bands, and for two way radio communication at VHF for aircrafts. 8. Amplitude modulation is prone to high levels of noise because most noise is amplitude based and obviously AM detectors are sensitive to it. 9. When two signals are modulated, they are said to “beat” with each other, creating additional frequencies called “beat frequencies”. 10. Unfortunately, amplitude modulation is subject to static interference from such things as household appliances — and especially from thunderstorms. 11. AM radio waves can end up hundreds and even thousands of miles away from where they started, and interfere with all other stations on the same frequency because of ionospheric refraction. 12. Nowadays, amplitude modulation is used for audio broadcasting on the long, medium and short wave bands, and for two way radio communication at VHF for aircrafts. 13. The envelope of the carrier can be seen to change in line with the modulating signal.