Where it all got started

It all started with the dawn of radio waves.

These waves were the most stealthy and
elegant. The Radio Waves are a type
of electromagnetic
radiation with wavelengths in
the electromagnetic spectrum longer
than infrared light. Radio waves
have frequencies from 300 GHz to as low as
3 kHz, and corresponding wavelengths ranging
from 1 millimeter (0.039 in) to 100 kilometers
(62 mi). Like all other electromagnetic waves,
they travel at the speed of light. Naturally
occurring radio waves are made by lightning, or
by astronomical objects. Artificially generated
radio waves are used for fixed and mobile radio
communication, broadcasting, radar and other
navigation systems, communications satellites,
computer networks and innumerable other
applications. Radio waves are generated
by radio transmitters and received by radio
receivers. Different frequencies of radio waves
have different propagation characteristics in the
Earth's atmosphere; long waves
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can diffract around obstacles like mountains and

follow the contour of the earth (ground waves),
shorter waves can reflect off the ionosphere and
return to earth beyond the horizon (sky waves),
while much shorter wavelengths bend or diffract
very little and travel on a line of sight, so their
propagation distances are limited to the visual
horizon.
To prevent interference between
different users, the artificial generation and use
of radio waves is strictly regulated by law,
coordinated by an international body called
the International Telecommunications
Union (ITU). The radio spectrum is divided into a
number of radio bands on the basis of
frequency, allocated to different uses.
ELECTROMAGNETIC INTERFERENCE (EMI)
Electromagnetic interference (EMI), also
called radio-frequency interference (RFI)
when in the radio frequency spectrum, is a
disturbance generated by an external source
that affects an electrical circuit by
electromagnetic induction, electrostatic
coupling, or conduction. The disturbance may
degrade the performance of the circuit or even
stop it functioning. In the case of a data path,
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these effects can range from an increase in error

rate to a total loss of the data. Both man-made
and natural sources generate changing
electrical currents and voltages that can cause
EMI: automobile ignition systems, cell phones,
thunder storms, the Sun, and the Northern
Lights. EMI frequently affects AM radios. It can
also affect cell phones, FM radios,
and televisions.
EMI can be used intentionally for radio jamming,
as in electronic warfare.
HISTORY OF RADIO WAVES
Radio waves were first predicted by
mathematical work done in 1867 by Scottish
mathematical physicist James Clerk Maxwell.
Maxwell noticed wavelike properties of light and
similarities in electrical and magnetic
observations. His mathematical theory, now
called Maxwell's equations, described light
waves and radio waves as waves of
electromagnetism that travel in space, radiated
by a charged particle as it undergoes
acceleration.
In 1887, Heinrich Hertz demonstrated the reality
of Maxwell's electromagnetic waves by
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experimentally generating radio waves in his

laboratory, showing that they exhibited the
same wave properties as light: standing
waves, refraction, diffraction, and polarization.
Radio waves were first used for communication
in the mid-1890s by Guglielmo Marconi, who
developed the first practical
radio transmitters and receivers.
What is Radio Propagation?
Radio propagation is the behavior of radio
waves when they are transmitted,
or propagated from one point on the Earth to
another, or into various parts of the atmosphere.
As a form of electromagnetic radiation, like light
waves, radio waves are affected by the
phenomena
of reflection, refraction, diffraction, absorption,
polarization, and scattering.
Radio propagation is affected
by the daily changes of water vapor in
the troposphere and ionization in the upper
atmosphere, due to the Sun. Understanding the
effects of varying conditions on radio
propagation has many practical applications,
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from choosing frequencies for

international shortwave broadcasters, to
designing reliable mobile telephone systems,
to radio navigation, to operation
of radar systems.
Radio waves travel at the speed of light. The
real number is 299792458.0 m/s exactly.
When passing through an object, they are
slowed according to that objects
permeability and permittivity.
The frequency of a radio wave
determines its propagation characteristics
through various media.
The Frequency bands
Band

Frequencies

Band

Frequencies

VLF (Very
Low)

10 - 30 kHz

VHF (Very
High)

30 - 300
MHz

LF (Low)

30 - 300
kHz

UHF (Ultra
High)

300 MHz 2.9 GHz

MF

300 kHz - 3

SHF (Super

2.9 GHz - 30

(Medium)

HF (High)

MHz

High)

GHz

3 - 30 MHz

EHF
(Extremely
High)

30 GHz and
above

The biggest use of radio waves is to carry

information, such as sound, 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, for
example
using amplitude
modulation
(AM), angle
modulation (which
can
be frequency
modulation or phase
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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.
A radio communication system sends signals
by radio (Radio waves). 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.
What did Hertz say?
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Hertz demonstrated how electromagnetic, or

radio, waves radiated across the "ether" at
the speed of light. Today we measure them in
units bearing his name. At the time of his
discovery, however, Hertz declared the
findings to be "of no use whatsoever."
Why the word RADIO?
This word was coined by the Edouard Branly,
French Physicist in the year 1897. In one of his
papers, referring to radio etymology, the
prefix radio, in the sense of wireless
transmission was first seen the term
radioconductor. The word however, was based
on the verb to radiate. Moreover, the word
also appeared in a 1907 article by Lee De
Forest.

Wireless Technology
Wireless communication is the transfer of
information between two or more points that
are not connected by an electrical conductor.

The most common wireless technologies

use radio. With radio waves distances can be
short, such as a few meters for television or
as far as thousands or even millions of
kilometers for deep-space radio
communications. It encompasses various
types of fixed, mobile, and portable
applications, including two-way
radios, cellular telephones, personal digital
assistants (PDAs), and wireless networking.
Other examples of applications of
radio wireless
technology include GPS units, garage door
openers, wireless computer mice,
keyboards and headsets, headphones, radio
receivers, satellite television, broadcast
television and cordless telephones.
What is modulation?
This is so important to cover yet I know
nothing. It means to change any properties of
a wave, wow, thats so precise.