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Lesson 11

Text: Main task and application of radio

Pre-text exercises:

I. Find the Ukrainian equivalents for the following English words and word combinations:

a) discharge, inventor, re­flect, cohere, satellite, aerial, sound travels, broadcasting, the number of times, the currentalternates, decides the frequency;

b) відбивати, супутник, сателіт, винахідник, кількість разів, звук передається, радіомовлення, розряд, струм змінює свій напрям, бути пов’язаним, визначати частоту, антена, повітряний.

II. Read and translate the text: “RADIO”

In the early days of the telegraph and the telephone, men observed that signals sometimes jumped across the space between wires running next to each other, so that messages sent to one person went to another. They realized that elec­tricity could pass through the air as well as along a wire. Just as sound travels through the air in waves, so elec­tricity travels through the air in what we call radio waves. A. S.Popov, a Russian inventor, had the idea of sending messages by radio waves, or " by wireless". He constructed a coherer detector for the study of lightning discharges and his receiver was described in 1895.

In fact, the radio waves travel in a straight line, but they are reflected from the sky back to the earth's surface. This is how radio waves travel around the world. You have heard on the radio of " long-wave transmissions" and " short-wave transmissions". In fact, there are two ceilings in the sky, not solid ceilings like the ceiling in a room, but more like nets which allow some radio waves to pass through them and re­flect others. The lower ceiling is called " Heaviside layer". This reflects long waves. Short waves are reflected by the higher ceiling, called the " Appleton layer". Radio transmit­ters can also send out ultra-short waves. These waves pass through both layers in the sky but are useful for communicat­ing with spaceships and can even be used to send sound to very long distances when they are reflected from satellites in space. It was exciting to be able to communicate over long dis­tances by signals sent by wireless, but soon men wanted to try to broadcast the sound of voices and even music in this way. A modern broadcast transmitting station has an aerial from which sound waves combined with carrier waves are transmitted. These waves are received on the radio sets in people's houses.

However, broadcasting like this would not be possible without the use of valves in the transmitting station and in­side the radio sets. Radio waves are sent out by alternating current. Valves at the transmitting station are used to keep the electric circuits oscillating, that is, sending the current backwards and forwards in the aerial. The number of times the current alternates decides the frequency, or wave-length, on which the station is broadcasting radio waves. Valves inside radio sets oscillate the current from the which are received. By turning a tuner you can arrange that the oscillations of the circuits in your radio set are the same as those at one of the broadcasting stations. We say, that you are " tuning in" to that broadcast.

Valves inside your radio set have two other uses. Firstly, they change alternating current into direct current, and it is direct current that goes to the loud speaker in the radio. It makes the centre of the loud speaker vibrate to produce the sound waves that you hear. Secondly, the valves amplify the very small amount of electrical energy received from the transmitter. This energy would be far too little to be any use if it were not amplified by a valve.