Unit 12

I. Выпишите из Прил. 1 значения следующих слов, запомните их:

pick up (v), exactly (adv.), height (n), tune (v).

П. Выпишите из Прил.2 значения следующих терминов, запомните их:

carrier wave

audio frequency

III. Образуйте существительные от следующих глаголов, используя суффиксы -er, -ion, -ture, -ence.

communicate, modulate, produce, act, transmit, convert, vary, mix, amplify, receive, differ.

IV. Дайте русский эквивалент следующих словосочетаний:

continuous high-frequency current, audio-frequency and radio-frequency currents, amplitude modulation, frequency modulation, microphone current, radio-frequency carrier, carrier wave frequency.

V. Прочтите, текст, выберите соответствующую форму глагола из представленных в скобках. Дайте краткое изложение содержания текста по-русски или по-английски.

1. We can only (communicate, communicated, communicating) information by radio waves by changing the wave in some way. This change is (know, knew, known) as modulation. The simplest form of modulation (are, is, were) to turn the wave on and off. This method was (use, used, using) in the early days of radio for telegraphic signals. The wave was (stops, stopped, stopping) and started to represent the dots and dashes of the Morse code by means of a telegraph key.

2. Speech and music (produce, producing, produces) audio frequencies which cannot be (transmitted, transmit, transmitting) directly. But they can be used to modulate radio waves. The modulated wave is then transmitted. When it is (receive, received, receives), the wave is demodulated and the original audio-frequency signal is recovered (восстанавливать). The high frequency radio wave (act, acting, acts) only to carry the audio-frequency signal and is (call, calling, called) the carrier wave. The audio-frequency signal is termed the modulating signal.

3. A wave (have, has, had) three quantities: amplitude, frequency and phase. Any of these quantities can be modulated. The two commonest methods of modulation (is, was, are) amplitude modulation, AM, and frequency modulation, FM.

VI. Прочтите текст, найдите абзац, в котором говорится oб амплитудной модуляции, скажите, в чём ее суть.

MODULATION (I)

1. The first radio message were sent in Morse code. The radio waves from the transmitter are switched on and off by pressing and releasing a telegraph key to form a pattern of dots and dashes which are then picked up by the aerial of the receiver.

2. For the transmission of speech and music the sound waves are converted by a microphone into an oscillating electric current which varies at the same frequency (audio frequency) as the sound wave. An oscillator produces a continuous high-frequency (radio-frequency) current which has a fixed frequency of between 100 kilohertz and 1000 megahertz. This current produces the carrier wave. The audio-frequency and the radio-frequency currents are mixed in the transmitter so that the carrier wave is modulated by the audio-frequency current in exactly the same way as the sound fed into the microphone. If the signal has to travel a long way it is amplified before transmission.

3. A wave may be modulated in different ways. Amplitude modulation (AM) is the method by which the amplitude or height of the carrier is changed by the microphone current. When the modulated wave is picked up by a receiver the sound-frequency wave is separated by valves or transistors from the radio-frequency carrier. It is amplified and the original sound is reproduced by the loudspeaker. Different transmitters use carrier waves of different frequencies so that the receiver must be tuned to pick up the carrier wave frequency of the required station.

(1.500)

VII. Задания к тексту.

Найдите в тексте интернациональные слова, переведите их, не пользуясь словарем.

Прочтите 1 абзац текста, выразите его содержание одним предложением.

Прочтите 2 и 3 абзацы текста, опишите процесс передачи и воспроизведения звуковой волны. Переведите текст абзацев.

VIII. Прочтите и переведите следующие предложения, обращая внимание на различные значения подчёркнутых слов.

1. Electronic computers are the only kind of machine with which one could hope to translate from one language into another. 2. There is only one paper devoted to the subject discussed. 3. As a test the metal was subjected to great heat. 4. Cooling systems have to be installed to prevent the computer from getting too hot. 5. This tube should be replaced too. 6. To carry out the experiment took us about one hour. 7. They were told about the latest developments in the field of microelectronics.