The story of radio

Without understanding the inquiries of pure science, we cannot follow the story of radio. It begins perhaps with Joseph Henry, an American physi­cist, who discovered in 1842 that electrical discharges were oscillating. A gi­gantic step forward was taken by James Maxwell, a Scottish physicist and one of the great mathematical geniuses of the 19-th century. By purely mathematical reasoning, Maxwell showed that all electrical and magnetic phenomena could be reduced to stresses and motions in a medium, which he called the ether. Today we know that this "electrical medium" does not exist in reality. Yet the concept of an ether helped greatly, and allowed Maxwell to put forward his theory that the velocity of electric waves in air should be equal to that of the velocity of light waves , both being the same kind of waves, merely differing in wave length.

In 1878, David Hughes, an American physicist, made another impor­tant discovery in the pre-history of radio and its essential components. He found that a loose contact in a circuit containing a battery and a telephone re­ceiver (invented by Bell in 1876) would give rise to sounds in the receiver which corresponded to those that had impinged upon the diaphragm of the mouthpiece. In 1883, George Fitzgerald, an Irish physicist, suggested a method by which electromagnetic waves might be produced by the discharge of a con­denser. Next we must turn to Heinrich Hertz, the famous German physicist, who was the first to create, detect and measure electromagnetic waves, and thereby experimentally confirmed Maxwell's theory of "ether" waves. In his experiments he showed that these waves were capable of reflection, refrac­tion, polarization, diffraction and interference.

A.S.Popov (1859-1906) demonstrated the world's first radio receiver which he called "an apparatus for the detection and registration of electric oscillations". By means of this equipment, Popov could register electrical disturbances, including atmospheric ones.

Marconi invented a system of highly successful wireless telegraphy, and inspired and supervised its application.

Such is the story of the many inventors of wireless telegraphy, work­ing with each other's equipment, adding new ideas and new improvements to them. During the first years of its development radio communication was called "wireless telegraphy and telephone". This name was too long for con­venience and was later changed to "radio" which comes from the well-known Latin word "radius"- a straight line drawn from the centre of a circle to a point on its circumference. Wireless transmission was named radio transmis­sion or simply "radio".

The term "radio" now means the radiation of waves by transmitting stations, their propagation through space and reception by receiving stations. The radio technique has become closely associated with many other branches of science and engineering and it is now difficult to limit the word "radio" to any simple definition.

TELEVISION

"Television" means "pictures from a distance". Television can show us live pictures of events on the other side of the world by means of receiv­ing images to the screen which are transmitted by systems of electro- or radiocommunication.

Two important pieces of television equipment are the camera and the receiver. The camera records an image of the scene it views on an electri­cally charged plate. A beam of electrons then sweeps back and forth across this plate. The result is electric signals which represent the brightness in dif­ferent parts of the scene. These signals are combined with a radio wave and sent out by a transmitter.

In a television system two separate transmitters are employed one for the sound channel and the other for the picture channel. The sound transmit­ter is frequency - modulated and simultaneously transmits the sound which accompanies the image. Each transmitter has its own antenna.

At the television receiver the amplitude modulated picture signals and the frequency-modulated sound signals that are transmitted on carriers are picked up simultaneously by a single antenna. The carriers differ in fre­quency so that they may be separated in the receiver. These signals are am­plified and separated by the circuit blocks. They reach the loudspeaker and the kinescope, respectively.

So the television receiver includes circuits for receiving, amplifying, and synchronizing the signals, and a large cathode-ray tube called a kine­scope. It converts the video impulses from the transmitting station into lumi­nous spots on a fluorescent screen. The "gun" of the tube fires a beam of electrons at the screen causing a spot of light. The television signals alter the strength of the beam and thereby the brightness of the spot. They also make the beam sweep back and forth in a series of lines of spots of varying bright-ness. The lines are very close together, and our eyes see them as a complete picture.