ТОР 5 статей:
V. Прочтите и устно переведите текст. Перепишите и письменно переведите 1, 2, 3 и 4-й абзацы.
The conversion of sound waves into electric currents and the amplification of these currents are two basic electronic techniques required for record players, different electronic techniques.
There are many reasons why it is not possible to transmit radio waves of very low frequencies, but for one things ( но, во-первых ) the transmitting aerial will be impossibly large. It is therefore not possible to broadcast electromagnetic waves of audio frequencies, and for long-distance transmission it is necessary to resort to higher frequencies and therefore shorter wavelengths.
3. In general, electromagnetic waves are propagated through the Earth’s atmosphere in two ways: travel over the surface of the Earth, and waves, which leave the surface of the Earth.
Long waves are transmitted over ground and therefore lose a good deal of their energy in passing through ground obstacles; they consequently have only a limited range. The shorter waves escape more easily from the surface of the Earth. Very short waves pass through the ionosphere so they can be used for long-distance communication. This is why the range of TV stations is limited.
This problem has been overcome in recent years by the use of communication satellite. If the satellite simply reflects the radiation, it is called a passive satellite, where if it receives the signal and retransmits an amplified signal, it is called an active satellite.