Английский язык: Методические указания и задания к контрольным работам для студентов специальности «Техническая эксплуатация транспортного оборудования», страница 22

1. Простейший приемник состоит из приемной антенны, резонансного контура, детектора и головных телефонов. 2. Приемная антенна принимает электромагнитные волны. 3. Резонансный контур обычно состоит из катушки индуктивности и конденсатора переменной емкости. 4. Резонансный контур дает возможность слушателю выбрать нужный сигнал из всех высокочастотных сигналов. 5. Резонансный контур иногда имеет постоянную емкость и катушку переменной индуктивности. 6. Детектор демодулирует выбранную радиоволну, выпрямляет ее и выделяет низкочастотную составляющую. 7. Головные телефоны (наушники) преобразуют низкочастотный сигнал в звуковые колебания. 8. Простейший приемник может быть улучшен применением источника питания, каскада высокочастотного усиления и каскада низкочастотного усиления.

Задание 5. Ответьте на вопросы.

1. What does the simpliest receiver consist of? 2. What is the purpose of the receiving antenna? 3. What is the purpose of the tuned circuit? 4. What is the purpose of the detector? 5. In what case may the simpliest receiver be improved? 6. What is the main difference between the simple receiver and the superheterodyne receiver?

Вариант 4

Задание 1. Прочитайте и переведите текст письменно.

Electromagnetic Waves

     To communicate by electronic means with the use of radiofrequency electromagnetic waves, both a transmitter and a receiver are required. For the most effective transmission and reception of signals, both the transmitter and the receiver should be connected to an antenna.

     The antenna. The antenna may be defined as a conductor or a system of conductors to radiate or to receive electromagnetic energy. The antenna of a transmitter acts like the primary coil of a transformer. The radio-frequency currents that flow in the antenna circuit of the transmitter produce varying electromagnetic waves. When these waves are intercepted by the receiving antenna, they induce a voltage of the same frequency in the antenna circuit of the receiver. The same antenna can be used to radiate electromagnetic waves or pick them up. For these reasons, antenna systems can be considered without dividing them into transmitting and receiving types.

     Radio waves, like all other kinds of electromagnetic radiation, have a number of common properties. Here we shall consider the main ones.

Dispersion of wave energy.  Radio waves emitted by the antenna propagate in all directions. As the distance from the antenna increases, the amount of wave energy at each point becomes progressively less. This effect is termed energy dispersion.

Radio wave absorption. When radio frequency energy is emitted from an antenna, part of this energy travels parallel to the earth and follows the curvature of the earth. This is called the ground or surface wave. The moving ground wave induces charges in the earth, which move with the wave. Consequently, the ground wave is attenuated or weakened rapidly

 due to the absorption by the earth. The degree of absorption is a function of the wavelength: the longer the wave, the lower is the energy absorption, in other words, the ground wave transmission can be used only with lower-frequency waves. Practically, ground wave communication is effective and reliable for short distances only.

VOCABULARY