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Many people contributed to the development of radio - there is no one single inventor. The existence of radio waves was predicted by the British mathematician Clerk Maxwell in the middle of the 19th century. Hertz, a German scientist was the first man to generate radio waves - that was in 1888.

The first 'wireless' message is claimed to have been sent across a laboratory by the Russian scientist Popov in 1896. Later that year the first experiments aimed at turning radio into a practical communication medium were carried out by Marconi in the garden of his father's villa in Italy. Several years later, Marconi astounded the scientific world by transmitting a message across the Atlantic from Cornwall to Newfoundland - a feat thought to be impossible.

Radio - kids facts about earth

Radio - facts about earth and technology (click to increase)

Model circuit diagram showing the components of the transistor radio receiver, including capacitors (C), resistors (R), transistors (T) and transformers (TR). An incoming signal starts at the aerial and finishes up as an audible sound at the loudspeaker at the other end (click image to increase)

Radio waves are generated by oscillatory electric currents. An important characteristic of them is their frequency which is the number of oscillations a second. Each station has its own particular frequency. A tuned circuit in the receiver selects the particular station we want. This circuit consists of a coil of wire and a component known as a capacitor which resonates at, and therefore gives preference to, one particular frequency.

Varying the value of the capacitor alters the resonant frequency and therefore the station to which the receiver is tuned. The radio signal selected by the tuned circuit is very weak and must be amplified up to many times its original strength before it can operate a loudspeaker. Amplification is provided by transistors or radio valves (tubes). A receiver also has a valve (tube) or transistor that extracts the voice or music from the radio wave.

The heart of a radio transmitter is a valve (tube) or transistor that generates an oscillatory current of precisely controlled frequency. The vibrations of a piece of quartz are normally used to control the frequency. After being amplified several times, the current is fed to the antenna which converts it into a radio wave.

Before reaching the antenna, however, the speech, music or telegraph signals to be carried by the radio wave are impressed on it by a process known as modulation. In one technique, the amplitude of the radio wave is made to vary in step with the variations in the amplitude of the speech or music.

This is known as amplitude modulation (AM). In an alternative technique, which gives better quality, the frequency of the radio wave varies in step with the variations of the speech or music. This is called frequency modulation (FM). Telegraph signals can either switch the radio wave on and off or switch its frequency back and forth between two valves.

Strange though it may seem, radio waves travel only in straight lines. Transatlantic transmissions are possible because the radio waves are bounced around the curvature of the Earth by the ionosphere. This is a layer of electrically charged (ionized) gases in the upper atmosphere. They are ionized by radiation from the Sun. Only short waves which cannot carry TV are reflected in this way. Today, telecommunications satellites in orbit around the Earth are used to relay microwave signals carrying TV programs around the world.

Microwaves are also used on the ground to carry the many thousands of telephone conversations and TV programs between large cities. Dish-shaped antennas on towers beam the signals from hilltop to hilltop. More interesting facts about earth and technology (radio) you can find on this page, for example 

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