Translate paragraph 4 in writing.
Write out of paragraphs 2, 3 the words and word combinations describing the radio transmitter. Use them for describing the radio transmitter to your group-mates.
6. Read and translate the sentences paying attention to the Sequence of Tenses:
a) The post-graduate said that the material he needed was not available at present.
b) The student said that he comprehended the aim of the experiment.
c) She said that she had comprehended the main idea of the article.
d) I was asked whether I could describe the technique of scanning reading.
e) He was asked if he would be able to derive from that English book the information we needed for our experiment.
f) The teacher said that scanning reading would be of great help to engineering students.
g) The student said that this material was not directly related to the information he was looking for.
h) He said he would not deal with the description of this experiment.
i) The students were told that they didn't need to read reference books carefully.
j) She said that she had lost the sense of a phrase and stopped reading.
Put the predicate of the main sentence in the Past Indefinite
Tense and change accordingly the Tense of the subordinate clause:
a) We are informed that many scientists are working at the problem of radioactivity.
b) Newspapers write that atomic radiation is very harmful and that, therefore, the stopping of H - bomb tests will greatly contribute to human health.
c) The United Nations scientific committee reports that every nuclear test contaminates the world by radioactivity and increases the danger to human life.
d) Scientists announce that they have discovered important properties of radioactive substances.
e) People are sure that soon a spaceship will fly to other planets.
f) Our first astronauts say that many astronauts are being trained for space travels.
g) The students say they solve many important problems in the field of physics.
h) The lecturer says that every element is made up of minute particles, which are called atoms.
i) Scientist says he writes articles on the development of science and technology.
j) It is known that electronics is becoming increasingly important in all branches of production.
Lesson Two
I. Pre-text Exercises
1. Learn the meaning and pronunciation of the following words:
convert [kənˈvə:t], oscillation [ɔsi'leiʃn], audible ['ɔ :dəbl], incoming [ˈinkΛmiŋ], video ['vidəou], intelligible [in'telidʒəbl], indiscriminately [indis'kriminitli], intermediate [intə'mi:djət], excessive [ik'sesiv].
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Read and remember the plural of the following nouns:
maximum ['mæksiməm] — maxima ['mæksimə]
medium ['mi:diəm] — media ['mi:diə]
minimum ['miniməm] — minima ['minimə]
quantum ['kwɔntəm] — quanta ['kwɔntə]
П. Read the following text carefully, while vou are reading look for the answers to the questions:
1. What are the essential components of a radio receiver?
2. What is the dominant consideration in receiver design?
3. What are the principal characteristics of a good radio receiver?
Text В
Receivers
l. The essential components of a radio receiver are an antenna for receiving the electromagnetic waves and converting them into electrical oscillations; amplifiers for increasing of intensity of those oscillations; detection equipment for demodulating; a speaker for converting the impulses into sound waves audible by the human ear (and in television a picture tube for converting the signal into visible light waves); and, in most radio receivers, oscillators to generate radio-frequency waves that can be "mixed" with the incoming waves.
2. The incoming signal from the antenna, consisting of a radio-frequency carrier oscillation modulated by an audio-frequency or video-frequency signal containing the impulses, is generally very weak. The sensitivity of some modern radio receivers is so great that if the antenna signal can produce an alternating current involving the motion of only a few hundreds electrons, this signal can be detected and amplified to produce an intelligible sound from the speaker. Most radio receivers can operate quite well with an input from the antenna of a few millionths of a volt. The dominant consideration in receiver design, however, is that very weak desired signals cannot be made useful by amplifying indiscriminately both the desired signal and undesired radio noise. Thus, the main task of the designer is to assure preferential reception of the desired signal.
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3. Most modern radio receivers are of the superheterodyne type in which an oscillator generates a radio-frequency wave of lower frequency; the latter is called intermediate frequency. To tune the receiver to different frequencies, the frequency of the oscillations is changed, but the intermediate frequency always remains the same (at 445 kHz for most AM receivers and at 107 MHz for most FM receivers). The oscillator is tuned by alternating the capacity of the capacitor in its tank circuit; the antenna circuit is similarly tuned by a capacitor in its circuit. One or more stages of intermediate-frequency amplification may be included in all receivers; in addition, one or more stages of radio-frequency amplification may be included. Auxiliary circuits such as automatic volume control (which operates by rectifying part of the output of one amplification circuit and feeding it back to the control element of the same circuit or of an earlier one) are usually included in the intermediate-frequency stage. The detector, often called the second detector, the mixer being called the first detector, is usually simply a diode acting as a rectifier, and produces an audio-frequency signal. FM waves are demodulated or detected by circuits known as discriminators or radio-detectors that translate the varying frequencies into varying signal amplitudes.
4. Radio-frequency and intermediate-frequency amplifiers are voltage amplifiers, increasing the voltage of the signal. Radio receivers may also have one or more stages of audio-frequency voltage amplification. In addition, the last stage before the speaker must be a stage of power amplification. A high-fidelity receiver contains both the tuner and amplifier circuits of a radio. Alternatively, a high-fidelity radio may consist of a separate audio amplifier and a separate radio tuner.
5. The principal characteristics of a good radio receiver are high sensitivity, selectivity, fidelity, and low noise. Sensitivity is primarily achieved by having numerous stages of amplification and high amplification factors, but high amplification is useless unless reasonable fidelity and low noise can be obtained. The most sensitive receivers have one stage of tuned radio-frequency amplification. Selectivity is the ability of the receiver to obtain signals from one station and reject signals from another station operating on a nearby frequency. Excessive selectivity is not desirable, because a bandwidth of many kilohertz is necessary in order receiver the high-frequency components of the audio-frequency signals. A good broadcast-band receiver tuned to one station has a zero response to a station 20 kHz away. The selectivity depends principally on the circuit in the intermediate-frequency stage.
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III. After-text exercises:
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