Radio The Early History of ”Radio”

Radio is the technology of using radio waves to carry information,

Radio such as sound,by systematically modulating properties of electromagnetic energy waves transmitted through space, 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,
for example using amplitude modulation or angle modulation (which can be frequency modulation or phase modulation).
Radio systems also need an antenna to convert electric currents into radio waves, and radio waves into an electric current.
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.-Justplay

A radio receiver receives its input from an antenna and converts it into a form that is 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 radios use only a small part of this spectrum.

A radio communication system sends signals by radio.
The radios 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.

Once generated, electromagnetic waves travel through space either directly,

or have their path altered by reflection, refraction or diffractionThe intensity of the waves diminishes due to geometric dispersion (the inverse-square law); some energy may also be absorbed by the intervening medium in some cases.
Noise will generally alter the desired signal; this electromagnetic interference comes from natural sources, as well as from artificial sources such as other transmitters and accidental radiators.
Noise is also produced at every step due to the inherent properties of the devices used. If the magnitude of the noise is large enough,
the desired signal will no longer be discernible; the signal-to-noise ratio is the fundamental limit to the range of radio communications.

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