Radio
Radio is the radiation (wireless transmission) of
electromagnetic signals through the atmosphere or free space. Information,
such as sound, is carried by systematically changing (modulating) some property
of the radiated waves, such as their amplitude, frequency, phase, or pulse
width. When radio waves strike an electrical conductor, the oscillating fields
induce an alternating current in the conductor. The information in the waves
can be extracted and transformed back into its original form.
Radio systems need a transmitter to modulate (change) some
property of the energy produced to impress a signal on it. Some types of
modulation include amplitude modulation and frequency modulation. Radio systems
also need an antenna to convert electric currents into radio waves, and vice
versa. An antenna can be used for both transmitting and receiving. The
electrical resonance of tuned circuits in radios allow individual stations to
be selected. The electromagnetic wave is intercepted by a tuned receiving antenna.
A radio receiver receives its input from an antenna and converts it into a form
usable for the consumer, such as sound, pictures, digital data, measurement
values, navigational positions, etc. Radio frequencies occupy the range from
a 3 kHz to 300 GHz, although commercially important uses of radio use only a
small part of this spectrum.
A radio communication system sends signals by radio. The
radio equipment involved in communication systems includes a transmitter and a
receiver, each having an antenna and appropriate terminal equipment such as a
microphone at the transmitter and a loudspeaker at the receiver in the case of
a voice-communication system.
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