Radio Communication (RADIO)

7/27/2019 Radio Communication (RADIO)

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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_frequency


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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

Documents

Radio Communication (RADIO)