Page 169 - merged.pdf

•Three Greatest Natural Discoveries that Drive Businesses 149

The two significant characteristics of electromagnetic-wave motion are the physi-
cal length of the wave and the number of times the wave cycle is repeated in a given
period of time.

Radio first became a possibility when the English physicist Michael Faraday
demonstrated that an electrical current could produce a magnetic field. In 1864
James Clerk Maxwell, a professor of experimental physics at Cambridge, proved
mathematically that these electrical disturbances could be detected at considerable
distances. Maxwell predicted that this electromagnetic energy could move outward
in waves, travelling at the speed of light. In 1888 Heinrich Hertz demonstrated that
Maxwell’s prediction was true for transmissions over short distances.

At this point the Italian physicist Marconi perfected a radio system that in 1901
transmitted Morse code over the Atlantic Ocean. Next came the development of the
vacuum tube, which amplified or strengthened the radio signal that was received at
an antenna; thus, much weaker signals could be transmitted and received than had
previously been possible.

It was next discovered that the electric current in a vacuum tube could be made
to oscillate. An electric-tube oscillator was thus able to generate very pure radio
waves. Reception was improved with the refining of the tuning circuit. These and
other components needed to produce radio receivers of acceptable quality under-
went rapid improvement in the period before World War II.

Individual broadcasting stations were assigned a portion of an arbitrary fre-
quency scale, so that the signal of one station would not interfere with each other.
Other frequency ranges have been reserved for the many additional uses of radio
signals, which include navigational aids for ships and aircraft, two way voice trans-
mission, and space and satellite communications.

Innovations after the war, especially the replacement of tubes by transistors and
of wires by printed circuits, drastically reduced the amount of power the receiver
needed to operate and allowed its components to be miniaturised. Other advances
included improvements in the sound fidelity of transmitting and receiving equip-
ment and the perfection of FM stereo broadcasting.