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RADIO COMMUNICATION (RADIO)
Radio is the wireless transmission of signals
through free space by electromagnetic
radiation of a frequency significantly below that
of visible light, in the radio frequency range,from about 30 kHz to 300 GHz. These waves
are called radio waves. Electromagnetic
radiation travels by means of
oscillating electromagnetic fields that pass
through the air and the vacuum of space.
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The transmission of information from one place using
radio waves as carriers, and their reception at
another distant place is known as radiocommunications. Since a radio wave is an
electromagnetic wave, it travels freely in air. A typical
radio communication system has two main
components: a transmitter and a receiver. At thetransmitting end, audio frequency (AF) signals are
converted into radio frequency (RF) for transmission.
On the receiving end, a radio receiver reconverts the
RF signal into an AF signal. Through this system
sound at a transmitting station is forwarded to thereceiving end and reproduced there.
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EXAMPLESOFRADIOCOMMUNICATIONSYSTEMS
Broadcasting
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Satellite communication
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Wireless local area network (WLAN)
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Mobile telephony
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Mobile Web
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HISTORY
James Clerk Maxwell showed mathematically that electromagnetic
waves could propagate through free space. Heinrich Rudolf Hertz and
many others demonstrated radio wave propagation on a laboratory
scale.
Nikola Tesla experimentally demonstrated the transmission and
radiation of radio frequency energy in 1892 and 1893 proposing that itmight be used for the telecommunication of information.
In 1895, Marconi built a wireless system capable of transmitting
signals at long distances (1.5 mi./ 2.4 km). From Marconi's
experiments, the phenomenon that transmission range is proportional
to the square of antenna height is known as "Marconi's law". Thisformula represents a physical law that radio devices use.
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Guglielmo Marconi demonstrated application of radio in commercial,
military and marine communications and started a company for the
development and propagation of radio communication services and
equipment. The field of radio development attracted many researchers,and bitter arguments over the true "inventor of radio" persist to this
day.
In 1907, Marconi established the first commercial transatlantic radio
communications service, between Clifden, Ireland and Glace
Bay, Newfoundland.The invention of amplitude-modulated (AM) radio, so that more than
one station can send signals (as opposed to spark-gap radio, where
one transmitter covers the entire bandwidth of the spectrum) is
attributed to Reginald Fessenden and Lee de Forest. On Christmas
Eve1906, Reginald Fessenden used an Alexanderson alternator androtary spark-gap transmitter to make the first radio audio broadcast,
from Brant Rock, Massachusetts. Ships at sea heard a broadcast that
included Fessenden playing O Holy Night on the violin and reading a
passage from the Bible.
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Inventor Edwin Howard Armstrong is credited with developing many of
the features of radio as it is known today. Armstrong patented three
important inventions that made today's radio possible. Regeneration,
the superheterodyne circuit and wide-band frequency modulation or FM.Regeneration or the use of positive feedback greatly increased the
amplitude of received radio signals to the point where they could be
heard without headphones. The superhet simplified radio receivers by
doing away with the need for several tuning controls. It made radios
more sensitive and selective as well. FM gave listeners a static-free
experience with better sound quality and fidelity than AM.
With the advent of the space program, radio engineers realized they
could now get long-range communications at the higher frequencies by
using satellites as radio relay stations. Thus came the development of
satellite communications systems. Today, practically all of our long-range
communication goes through satellite links. Since the firstcommunications satellite was placed in orbit, satellites have been
thought of as "the" communications system. However, as seen from a
military viewpoint, satellite systemsand most other radiosystemshave some weaknesses.
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The
electromagnetic
spectrum
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Super Low and Extra Low Frequency bands
300 Hz - 3 kHz. Ultra Low Frequency (ULF)
3 - 30 kHz Very Low Frequency (VLF)
30 - 300 kHz Low Frequency (LF)
300 kHz - 3 MHz Medium Frequency (MF)
3 - 30 MHz High Frequency (HF)
30 - 300 MHz Very High Frequency (VHF)
300 MHz - 3 GHz Ultra High Frequency (UHF)3 - 30 GHz. Super High Frequency (SHF)
30 - 300 GHz. Extra High Frequency (EHF)
Infrared
Visible Light
Ultraviolet
X rays
Gamma Rays
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RADIOSPECTRUMRadio spectrum refers to the part of
the electromagnetic spectrum corresponding to radiofrequencies that is, frequencies lower than around
300 GHz (or, equivalently, wavelengths longer than
about 1 mm).
Different parts of the radio spectrum are used for
different radio transmission technologies and
applications. Radio spectrum is typically government
regulated in developed countries and, in some cases, is
sold or licensed to operators of private radio
transmission systems (for example, cellular telephoneoperators or broadcast television stations). Ranges of
allocated frequencies are often referred to by their
provisioned use (for example, cellular spectrum or
television spectrum).
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Table of ITU Radio Bands
Band Number SymbolsFrequency
Range
Wavelength
Range
4 VLF 3 to 30 kHz 10 to 100 km
5 LF 30 to 300 kHz 1 to 10 km
6 MF 300 to 3000 kHz 100 to 1000 m
7 HF 3 to 30 MHz 10 to 100 m
8 VHF 30 to 300 MHz 1 to 10 m
9 UHF300 to
3000 MHz10 to 100 cm
10 SHF 3 to 30 GHz 1 to 10 cm
11 EHF 30 to 300 GHz 1 to 10 mm
12 THF300 to
3000 GHz0.1 to 1 mm
http://en.wikipedia.org/wiki/Very_low_frequencyhttp://en.wikipedia.org/wiki/Low_frequencyhttp://en.wikipedia.org/wiki/Medium_frequencyhttp://en.wikipedia.org/wiki/High_frequencyhttp://en.wikipedia.org/wiki/Very_high_frequencyhttp://en.wikipedia.org/wiki/Ultra_high_frequencyhttp://en.wikipedia.org/wiki/Super_high_frequencyhttp://en.wikipedia.org/wiki/Extremely_high_frequencyhttp://en.wikipedia.org/wiki/Tremendously_high_frequencyhttp://en.wikipedia.org/wiki/Tremendously_high_frequencyhttp://en.wikipedia.org/wiki/Extremely_high_frequencyhttp://en.wikipedia.org/wiki/Super_high_frequencyhttp://en.wikipedia.org/wiki/Ultra_high_frequencyhttp://en.wikipedia.org/wiki/Very_high_frequencyhttp://en.wikipedia.org/wiki/High_frequencyhttp://en.wikipedia.org/wiki/Medium_frequencyhttp://en.wikipedia.org/wiki/Low_frequencyhttp://en.wikipedia.org/wiki/Very_low_frequency7/27/2019 Radio Communication (RADIO)
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APPLICATION
Air bandAmateur radio frequencies
Marine band
Citizens' band and personal radio services
Industrial, scientific, medical
Land mobile bands
Radio control
Radar