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Bài giảng Tiếng Anh chuyên ngành Viễn thông - Unit 3 (part 2): Radio. This chapter presents the following content: Information transfer, reduced time clauses, word formation, describing a process. | TASK 3 Work in pairs A and B. Student A Read the text on sky waves and complete your section of Table 2 Student B Read the text on space waves and complete your section of Table 2 When you have finished ask your partner for the information to complete the table. sky skai space speis NOTE skyward skaiwad certain sa tn critical kritikal typical tipikl return ri ta n ionosphere ai ana fia layer leia molecule maliíkju l stretch stretf strike straik bounce bauns earthward a 9wad rellection ri llekfan attenuate a tenjuJeit season si zan gradually gr d3 uali refract ri fr kt TASK 3 Sky wave It travels skywards and if it is below a certain critical 10 frequency typically 30MHz is returned to earth by the ionosphere. This consists of layers of air molecules stretching from about 80km above the earth to 500km. On striking the earth 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 15 completely attenuated. The critical frequency varies with the time of day and the seasons. Sky waves of high frequencies can travel thousands of kilometres but at VHF and above they usually pass through the ionosphere into outer .