Unit 19

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

propagate (v), curvature (n), disadvantage (n), density (n), fade (v), artificial (a), scatter (v), launch (v).

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

ground wave radio blackout

space wave beam (v)

sky wave

III. Сгруппируйте антонимы, переведите их.

1. Advantage (n), artificial (a), reflect (v), loss (n), frequent (a), possible (a), scatter (v), upper (a), able (a).
2. 2. Collect (v), impossible (a), unable (a), seldom (a), gain (n), attract (v), natural (a), disadvantage (n), lower (a).

IV. Прочтите текст, выберите подходящую форму глагола из представленных в скобках. Переведите текст.

A signal from a transmitter can be (propagate, propagated, propagating) in three ways: by ground waves, by space waves and by sky waves. Ground waves (travel, travels, traveled) round the surface of the earth for short distances. As they travel, they (lose, lost, loses) energy. This loss of power, or attenuation, (depend, depends, depended) on the nature of the surface. Attenuation also (varies, varied, vary) with the frequency of the signal: the higher the frequency, the greater the ground wave attenuation.

Propagation by space waves (applies, apply, applied) mainly to very high frequencies. Part of the transmitted signal (travels, travel, travelling) in a direct line from transmitting antenna to receiving antenna. Partly the signal is (reflecting, reflected, reflect) from the ground. The higher the frequency, the greater the possible space wave’s reflection.

The range covered by ground waves and space waves is limited. Greater distances can be (achieve, achieved, achieving) using sky waves. Sky wave propagation depends on the ionosphere.

V. Прочтите текст, перечислите его основные положения.

RADIO WAVES

1. Radio waves travel outwards from a transmitting aerial in straight lines and do not follow the curvature of the Earth. Marconi was able to send a message across the Atlantic Ocean because there is an electric layer in the upper atmosphere which reflects the radio waves back to the Earth. In fact, several such electric layers have since been discovered. The Heaviside-Kennelly layer, or E-region, is about 90 to 150 km above the Earth's surface and the Appleton layer or F-region lies between 150 and 400 km. Both these layers consist of ionized gases and form part of the ionosphere. Radio waves, which travel by reflection from the ionosphere, are called sky waves.

2. Long radio waves are reflected by the E-region and short waves by F-region. However, the very short waves of VHF (very high frequency) and UHF (ultra high frequency) transmissions are not reflected but pass through the ionosphere into space. Television programs, which are broadcast on these high frequencies, therefore, cannot be reflected from the ionosphere. Another disadvantage of the ionosphere is that heights and densities of the layers constantly change, particularly during magnetic storms and periods of sunspot activity. This makes long-distance transmission fade and can cause a complete radio blackout.

3. An artificial reflector does not have these disadvantages. Early communication satellites such as the echo balloons were simply large balloons with metallic surfaces to reflect the radio waves. But the signals were scattered by the balloon in all directions and much of the power was lost. Telstar, an active satellite launched in July 1962 contains more than 2500 transistors. Signals beamed to it from one side of the Atlantic Ocean are retransmitted to the receiving aerial on the other side.

VI. Прочтите текст, назовите известные вам синонимы подчеркнутых слов.

Astronomers now have a great number of artificial satellites working for them. O.S.O. (Orbiting Solar Observatory) satellites, for instance, are making continuous observations of the gun. Others are studying the composition of the pressure and temperature of the upper atmosphere. The satellites of the most practical use to us are the intercontinental communication satellites that make long-distance television transmission possible. They are also used for international telephone calls instead of radio.