Category Communication

How do we receive messages and TV pictures from a satellite orbiting the Earth?

               Television pictures, radio and telephone communications are bounced off satellites to cover the greatest possible area of the world. Satellites orbiting the Earth must travel at high speed to escape being brought down by the Earth’s gravity. As the Earth itself is spinning rapidly, there is a point above the Earth’s surface where the orbiting speed of the satellite can be matched with the rotational speed of the Earth. At this point —35,900 kilometres above the Earth — the satellite appears to stand still and is said to be in a geostationary orbit.

Geostationary satellites can be positioned right over the areas where they are needed. They can also be used as spy satellites, because they remain constantly over a region of interest.

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How can television pictures be transmitted by radio waves?

               Television cameras break a picture into electrical signals, separating them into three colours (red, blue and green) and turning them into coded messages. Sound is recorded and coded at the same time. The coded pictures and sounds are transmitted by radio waves, electrical cables or optical fibres to the receiver. Inside a television receiver the signals travel to three electron guns — one for each colour. The electron guns emit streams of electrons, which are directed at a fluorescent screen. Magnets bend the electron streams so that they scan back and forth from top to bottom, exciting the phosphors in the screen and producing a colour image. They scan so quickly that our eyes see the images as a continuous picture.

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How does a telephone work?

               Telephones transmit speech messages along wires by means of electrical signals. Telephones were invented as long ago as 1876.The handset of a telephone includes a loudspeaker and a very small microphone, which contains granules of carbon. When you talk into the microphone the sound waves of your voice cause a metal diaphragm to vibrate, and it presses against the carbon granules. The vibrations vary depending on the sounds. They change the very small amount of current flowing out along the wires to the receiver of another telephone.

               When the electric current carrying the signals reaches the receiver handset, the same variations in the current run through an electromagnet. This causes another diaphragm to vibrate in the earpiece, accurate reproducing the sound of the speaker’s voice.

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What are communications?

               We exchange ideas and messages by communication. Humans, as well as other animals, communicate visually and by sounds. Some animals also communicate by means of smells that convey messages. Humans differ from all other living things because we can communicate by means of symbols. These are compressed pieces of information, such as written letters or numbers that actually communicate very complex ideas.

 

 

 

 

 

 

 

 

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What are radio waves?

          Radio waves belong to the family of electromagnetic waves which owe their existence to moving electrons. The existence of radiowaves was first predicted by James Clerk Maxwell in 1860, but it was not until 1887 that Heinrich Hertz succeeded in producing them experimentally. “Wireless” telegraphy was first demonstrated by Sir Oliver Lodge in 1894 and it was Guglielmo Marconi, the Italian scientist, who could first successfully transmit a long distance transmission in 1900 with the help of radiowaves.

          It is through radio waves only that sound from the broadcasting station is able to reach our radios. Their use is also made to transmit a variety of programmes. Radio waves work as the carriers for communication signals. The message is modulated with radio waves and transmitted with the help of a transmitter. The modulated signal is received by the radio receiver and then decoded. Radio waves were also used to keep in contact with the flying planes. With the help of these waves they are properly guided and controlled during flights thus avoiding accidents.

          Radio waves are in fact invisible electromagnetic waves which travel with the speed of light, i.e. at 300,000 km. per second. Satellites and spacecrafts keep in contact with the earth stations with the help of these waves. Live communication with the satellites and astronauts has become possible only due to radio waves. These waves can travel both through the air and the vacuum. They can even travel in water and underground to a distance of a few metres. Communication is established between the ships with the help of these waves. Every ship is equipped with radio transmitters and receivers.

          To study the radio waves originating from the different heavenly bodies, scientists make use of radio telescopes. With the help of these telescopes, it has now become possible to identify the planets and stars which generate the radio waves.

          Radio waves are also used by police. They have the equipments by which they can send and receive messages from moving vehicles. Fire brigades also use of radio waves while providing help in accidents. These waves are also used to control traffic. Today we have the instruments which can measure the speed of a moving vehicle from the control room itself.

          In a nutshell, we can say that the world has shrunk due to these radio waves.