March 12, 1995
Radio is a form of communication in which intelligence is transmitted without
wires from one point to another by means of electromagnetic waves. Early forms
of communication over great distances were the telephone and the telegraph. They
required wires between the sender and receiver. Radio, on the other hand,
requires no such physical connection. It relies on the radiation of energy from
a transmitting antenna in the form of radio waves. These radio waves, traveling
at the speed of light (300,000 km/sec; 186,000 mi/sec), carry the information.
When the waves arrive at a receiving antenna, a small electrical voltage is
produced. After this voltage has been suitably amplified, the original
information contained in the radio waves is retrieved and presented in an
understandable form. This form may be sound from a loudspeaker, a picture on a
television, or a printed page from a teletype machine.
The principles of radio had been demonstrated in the early 1800s by such
scientists as Michael Faraday and Joseph Henry. They had individually developed
the theory that a current flowing in one wire could induce (produce) a current
in another wire that was not physically connected to the first.
Hans Christian Oersted had shown in 1820 that a current flowing in a wire sets
up a magnetic field around the wire. If the current is made to change and, in
particular, made to alternate (flow back and forth), the building up and
collapsing of the associated magnetic field induces a current in another
conductor placed in this changing magnetic field. This principle of
electromagnetic induction is well known in the application of transformers,
where an iron core is used to link the magnetic field of the first wire or coil
with a secondary coil. By this means voltages can be stepped up or down in value.
This process is usually... [continues]
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"Radio: a Form of Communication." StudyMode.com. 10, 1999. Accessed 10, 1999. http://www.studymode.com/essays/Radio-Form-Communication-3183.html.