Transmission of Radio- and Audio-frequency Power by Lines
An important use of transmission lines is in carrying radio-frequency power from a transmitter to an antenna or from an antenna to a radio receiver. Lines used for this purpose are commonly said to be resonant or nonresonant, according to the method of operation.
Nonresonant Lines. In the nonresonant lines, the terminating impedance ZL at the endto which the line delivers the power is made equal to the characteristic impedance. The power loss and peak voltage to which the line is subjected are then less than with any other mode of operation.
The losses in a nonresonant line depend upon the line attenuation l, and are usually expressed in decibels, using the relation:
Decibels = 8.686 αl.
With air insulation the attenuation constant α at radio frequencies is universally proportional to the linear dimension of the line.
Resonant Lines. When the load impedance does not equal the characteristic impedance, a reflected wave exists, and the line is said to be resonant because of the resulting oscillatory character of the current and voltage distributions. Resonant operation has the advantage of not requiring an impedance match between the line and the load. At the same time it has the disadvantage that the average power factor along the line is lower than with resonant operation. This results in increased power loss and greater voltage stress in proportion to transmitted power for the corresponding nonresonant case. Nonresonant operation also leads in many cases to loss in power transferred, as a result of mismatching.
Задание 3. Составьте аннотацию к тексту на русском или на английском языке.
Вариант 3
Задание 1. Переведите следующие предложения на русский язык:
1. The model having been tested we could recommend it for mass production.
2. If we want some information to be sent rapidly we send it by radio.
3. One should use new research methods, not the old ones.
4. The work is often referred to in special literature.
5. Much data was accumulated concerning the condition of life and work in space before the beginning of further investigations.
Задание 2. Прочтите текст и переведите его на русский язык в письменной форме, пользуясь словарем.
From the history of radio communication
Radio communication and broadcasting was one of the first important uses electronics was put to. Simple radio transmitters and receivers had existed already long before the application of electronics made them what they are today; the existence of electromagnetic (radio) waves was predicted as early as 1865 in a mathematical treatise by Professor Clerk Maxwell, an English scientist. The German scientist Heinrich Hertz had verified the existence of them as mysterious waves in 1887 using an elementary spark transmitter and detector. A somewhat sophisticated system, using an elevated antenna, and an improved detector, sent out the first dot-dash radio-telegraphy messages in 1896. The ranges of this communication system was two miles, just beyond shouting range.
A milestone in radio communication occurred on a December day in 1901 in Newfoundland, when the young Italian Guglielrmo Marconi and his associates succeeded in spanning the Atlantic with faint buzzes, the letter "3" of the Morse code. Further attempts, in 1902, to initiate a commercial transatlantic radio telegraph service failed, however, of the seasonal variations in signal strength which nobody had suspected.
Radio telegraphy and telephony continued to make slow and erratic progress in the following years, but it was not until 1907 that the invention of the crystal detector and Leo De Forest's audition (triode) tube finally brought into fruition. Two years later in 1909, De Forest broadcast a Metropolitan opera by radio-telephone, a feat that forecast our present system of commercial radio broadcasting.
Задание 3. Составьте аннотацию к тексту на русском или на английском языке.
Вариант 4
Задание 1. Переведите следующие предложения на русский язык:
1. The results were reproduced in space flight under the conditions of overloading and weightlessness.
2. Advancement in electronic techniques appears to be endless.
3. The session was over, with many aspects of the problem left unsolved.
4. The velocity of a moving object can change by its speeding up, slowing down, or changing its direction of motion.
5. There are certain principles to be followed in the design of this device.
Задание 2. Прочтите текст и переведите его на русский язык в письменной форме, пользуясь словарем.