Английский язык: Методические указания и задания к контрольным работам для студентов специальности «Техническая эксплуатация транспортного оборудования», страница 23


as the result of

в результате

becomes progressively less

все более уменьшается

 Задание 2. Переведите слова и словосочетания.

attenuation; absorption; primary coil; dispersion; to increase the amount of wave energy; the curvature of the earth; to induce charges in the earth; the longer the wave, the lower is the energy absorption; surface (ground) wave; radiomagnetic waves are intercepted by the receiving antenna; the amount of wave energy.

Задание 3. Переведите слова и словосочетания.

поверхностная волна эффективна и надежна; из-за поглощения землей; поверхностная волна затухает или быстро слабеет; принимать и излучать электрические волны; распространяться по земле; радиоволны излучаемые антенной; рассеяние энергии; когда волны перехватываются приемной антенной; первичная обмотка трансформатора.

Задание 4. Ответьте на вопросы.

1. What is the antenna?

2. What happens when the waves from the transmitting antenna are picked up by the receiving antenna?

3. What is energy dispersion?

Задание 5. Переведите предложения.

1. Радиоволны распространяются со скоростью света.

2. Частоты свыше 20000 колебаний в секунду называются радиочастотами.

3. Антенна излучает и принимает электрические волны.

4. Поверхностная волна распространяется параллельно земле.

5. Поверхностная волна затухает или слабеет из-за поглощения землей.

6. Поверхностная волна надежна и эффективна только для небольших расстояний.

Вариант 5

Задание 1. Прочитайте и переведите текст письменно

Electromagnetic Waves

Wave reflection and refraction. Radio waves propagate rectilinearly only in a uniform medium. When waves pass from one medium into another, wave reflection and refraction take place at an angle of incidence equal to the angle of reflection. The higher the difference in dielectric constants of the media and the longer the operating wavelength, the higher is the degree of refraction.

Wave diffraction. An opaque obstacle in the path of propagation causes radio waves to skirt around this obstacle. This effect is known as diffraction. The longer the wave the better it passes around an obstacle. Radio waves propagating along the surface of the Earth and partly rounding it due to diffraction effects are called ground or surface waves. Radio waves propagating around the earth due to reflections from ionosphere and the ground are called space or sky waves.

     The sky wave. It is called so because the energy from the antenna is radiated at an angle toward the sky.

     It has been found that VHF signals may travel great distances with very little attenuation, since at these frequencies the ionosphere and the earth’s surface serve as excellent reflectors and produce a duct that guides electromagnetic waves. By applying this waveguide principle, it is possible to employ multihop transmissions via the sky wave and to establish radio communication between points separated by great distances. Since the maximum distance covered in a single hop cannot exceed 2,500 miles, a signal requires five hops to reach the opposite side of the Earth.

     When the sky wave is directed at a low angle toward the ionosphere, the signal will be returned to the earth at a greater distance from the transmitter. The distance decreases as the angle of radiation is increased. When this angle reaches certain value known as the critical angle, the waves will penetrate the ionosphere and will fail to return. The value of this critical angle is not a constant but varies with changing ionospheric conditions, and also depends on the frequency of the radio wave that is being transmitted.

Sky wave transmission is important since it provides the primary means of communication around the world via short waves.