place. 2. With tubes containing grid structures, the heating of each grid must be taken into account. 3. One of the limitations that should be taken into consideration is the peak emission current. 4. Ohm's law holds true for all circuits both direct and alternating. 5. The grid of a vacuum tube may be flat, round, or oval to meet the demands of design. 6. Having been tested the machine was successfully put into operation. 7. The discovery of the Vavilov-Cherenkov effect was of outstanding importance for further developments

11.9 Переведите вопросы

1.Что такое триод? — Триод это лампа, которая содержит третий элемент. 2. Как называется третий элемент? — Третий элемент называется сеткой.

3.Где находится сетка? — Она находится между катодом и анодом. 4. Какой вид имеет сетка? — Она имеет вид спирали. 5. Могут электроны свободно проходить через нее? — Да. 6. Что ближе к сетке, анод или катод? — Катод ближе к сетке. 7. В каком случае электроны не притягиваются к сетке? — ... если сеточный потенциал является отрицательным по отношению к катоду. 8. Что происходит в этом случае? — В этом случае нет сеточного тока.

12Lesson 12

12.1 Прочтите следующие слова согласно транскрипции

parametric, obscure, variable, immediately, quantum, compare, linear, capacitan, associate, idler, circuitry, inherent

12.2 Прочтите слова, обращая внимание на перемещение ударения

parameter — parametric; amplify — amplification; similar — similarity; product — production; generate — generation

12.3 Сгруппируйте синонимы

begin , work, ordinary, at once, use, in the sphere of, operate, start, immediately, usual, in the field of, employ, remain, stay.

12.4 Сгруппируйте антонимы

dependent, negative charge, cover, nowhere, developed, undeveloped , everywhere, discover, positive charge, independent.

12.5 Прочтите вопросы перед каждым абзацем текста и найдите ответы в тексте

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1.Were semiconductor diodes used as active devices? 2. When was the tunnel diode developed? 3. What does the operation of parametric diode depend on? 4. Of what nature is the parametric diode?

12.6Найдите в первом абзаце текста предложение, содержащее субъектный инфинитивный оборот

12.7Прочтите и переведите текст

Parametric and tunnel diodes

1.The history of the semiconductor diode is held to have begun in the early days of radio when "crystals" were used as signal detectors. However, the operating mechanism of the semiconductor diode remained obscure until the introduction of modern transistor physics. Furthermore, semiconductor diodes were not used as active devices until a p-n junction diode was discovered to be an attractive element for parametric amplifiers. Such a diode, characterized by a variable capacitance, is known to be called a parametric diode. It has a voltage-dependent junction capacitance. In some commercial forms it is also known as a "varactor" diode.

2.Immediately after the introduction of parametric diodes, another semiconductor diode known as the tunnel diode was developed. The tunnel diode is a semiconductor p-n junction somewhat similar to the parametric diode, although its physical principles of operation are entirely different. The operation of the tunnel diode is based on quantum-mechanical tunneling. Parametric diodes and tunnel diodes may be compared as follows:

a) They are both p-n junctions. Physically, they can be manufactured in much the same manner.

b) The operation of parametric diode depends on its nonlinear capacitance, controlled by the applied voltage, while the operation of a tunnel diode depends on its negative resistance, made possible by the tunneling current.

c) They are both two-terminal, negative-resistance devices. In parametric amplifiers using parametric diodes the negative resistance is derived from an r-f pump through a nonlinear interaction, while in tunnel-diode amplifiers, negative resistance is produced by a simple d-c source.

d) In a tunnel-diode amplifier the gain-bandwidth product is inversely proportional to the product of the diode capacitance and negative resistance, while in a pa- rametric-diode amplifier the gain-bandwidth product is inversely proportional to the Q of the associated idler circuit.

e) The parametric diode is of a reactive nature, and thus generates very small excess Johnson noise. The noise from a parametric amplifier originates essentially from the associated circuitry. As the tunnel diode is dependent on a tunneling stream of electrons, it has an inherent shot noise.

12.8 Переведите словосочетания

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signal detector, p-n junction diode, parametric amplifiers, tunnel diode, nonlinear interaction, associated idler circuit, shot noise, quantum mechanical tunneling, gain bandwidth product, variable capacitance, excess noise, semiconductor diodes, modern transistor physics, appropriate frequency, a travelling wave tube, intermediate undisturbed level, in addition to amplifying radiowaves, two terminal negative resistance devices.

12.9 Ответьте на вопросы

1. When did the history of the semiconductor diode begin? 2. What was ap-n junction diode for parametric amplifiers? 3. What is called a parametric diode? 4. What was developed after the introduction of parametric diode? 5. Are the principles of operation of a tunnel diode and of a parametric diode the same? 6. What is the operation of the tunnel diode based on? 7. In what way may parametric diodes and tunnel diodes be compared?

12.10Выпишите из первого абзаца текста предложение, содержащее субъектный инфинитивный оборот

12.11Переведите, обращая внимание на корневые слова и их произ-

водные

conduct, conductor, conductance; detector, detection; introduce, introduction; attract, attraction, attractiveness; vary, variable; depend, dependent, dependence, immediate, immediately; differ, different, difference; resist, resistor, resistance; amplify, amplifier, amplification; essential, essentially.

12.12 Определите, какой частью речи является каждое слово

commercial, transistor, parametric, capacitance, junction, inversely, reactive, essentially, inherent.

12.13 Найдите в тексте слова и словосочетания, эквивалентные дан-

ным

однако; до тех пор пока не; такой; в качестве; следующим образом; таким же способом; в то время как; оба ;таким образом; так как; кроме того; немедленно; после; хотя.

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13 Lesson 13

13.1. Прочтите следующие слова согласно транскрипции

electrostatics , instability, shield , reasonable , tetrode, adequate , component, variation , consequence, altogether, mutual, divert.

13.2 Прочтите следующие слова, обращая внимание на перемещение ударения

opposite — opposition; equal — equality; amplify — amplification; stable— stability; vary— variation.

13.3 Сгруппируйте синонимы

affect, tube, determine, on account of, permit, apply, define, due to, allow, employ, valve, influence.

13.4 Прочтите и переведите текст

Tetrodes

1.It has been noted that the A.C. grid and plate potentials are opposite in phase. As a result, the A.C. potential difference between these two elements is considerable, being equal in magnitude to the sum of the A.C. input and output voltages. On account of the electrostatic capacitance between grid and plate, this potential difference produces a current flow from the output circuit to the grid by condenser action, and under certain load conditions such reaction of feedback causes the amplifier to become unstable. The instability may be avoided by inserting an electrostatic shield in the form of a screen grid between the plate and the original grid which in this arrangement is known as the control grid. A tube of this type is known as a tetrode, or screen-grid tube.

2.To permit the flow of reasonable amounts of electron current, the screen must be operated at the positive potential. For adequate shielding of the control grid, however, the screen potential should have no A.C. component, and this must be carefully considered in any circuit application.

3.The fact that the screen grid acts to shield the control grid from variations of plate potential means also that the cathode is shielded from the plate. As a consequence, electron emission is affected only very slightly by the plate potential; it is determined almost altogether by the control-grid and screen-grid potentials. A portion of the electron stream passes to the screen on account of its positive potential, and forms the screen current; the remainder, usually a much larger part, flows to the plate.

4.In terms of tube characteristics, since a relatively large change of plate potential causes very little change in plate current, the value of rp (the internal plate re-

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sistance), is much larger than for the triode. For the same reason, the amplification factor is greater for a tetrode than for a triode. The mutual conductance Gm, however, is of about the same magnitude as for a triode, although it is somewhat reduced by reason of the fact that a portion of the emission current is diverted to the screen.

5. For receiving-type tetrodes, rp is of the order of a megohm, and has a magnitude of several hundreds.

13.5 Переведите словосочетания

a)potential difference; A.C. input and output voltages; condenser action; load conditions; screen-grid tube; the value of the internal plate resistance; receiving-type tetrodes.

b)for the same reason, as a consequence, in terms of tube characteristics, in terms of this fact, on account of the electrostatic capacitance, by reason of this phenomenon.

13.6 Ответьте на вопросы

1. Why is the A.C. potential difference between the grid and plate considerable? 2. Why does this potential difference produce a current flow from the output circuit to the grid? 3. How may the instability be avoided? 4. At what potential must the screen be operated to permit the flow of reasonable amounts of electron current? 5. What fact implies also that the cathode is shielded from the plate? 6. How is electron emission affected by the plate potential? 7. On account of what potential does a portion of the electron stream pass to the screen? 8. Why is the value of the internal plate resistance much larger than for the triode?

13.7 Переведите следующие слова, обращая внимание на префикс un-

unstable, unequal, unsteady, unusual, unaffected, unshielded.

13.8 Расшифруйте сокращения

d.c., a.c., т.е., c.p.s., p.h., r.f, k.c., u.h.f

13.9 Прочтите диалог в ролях

Dialogue

A.I hear you have entered the Radio Engineering faculty.

B.Yes, I want to be a radio engineer, like you.

A.Glad to hear that. Really, it's a very interesting speciality. I suppose you are interested intechnical journals on your future specialty, aren't you?

B.Yes, I am fond of radio engineering, and I've read a great many articles concerning this subject but sometimes I come across many things I don't understand.

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