chap 2 & 3 em & freq

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1Connected Schools Wireless Communication TrainingModule I: Wireless Basic Concept

Module 1: Wireless Basic Concept

II. What is an ElectromagneticWave

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II. What is an Electromagnetic Wave ?

Also known as Electromagnetic Radiation

General Information

=> One Theory linking masse moving and wavelength

One natural aspect, Two property aspects

- Corpuscular -> photon

- Wave -> electromagnetic radiation

UV, IR, X-ray

Important physical element that has:

- Propagation Properties in the vacuum and in the matter

- Matter interaction property

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Electromagnetic energy = Term used to describe all the different kinds ofenergies released

into space (ex: by stars such as the Sun)

These kinds of energies include:

Radio Waves

TV waves Radar waves

Heat (infrared radiation)

Light

Ultraviolet Light (This is what causes Sunburns)

X-rays (Just like the kind you get at the doctor's office)

Short waves

Gamma Rays Microwaves, like in a microwave oven

N.B: - They all travel in waves, like the waves at a beach or like sound waves (are also made of tiny particles)

- The fact that electromagnetic radiation travels in waves lets us measure the different kind

by wavelength or how long the waves are

What is electromagnetic radiation (1/2) ?

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A propagating wave in space with electrical (E) and magnetic (M) componentsWhat is electromagnetic radiation (2/2)?

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E and M oscillate perpendicular to each other and to the direction of

the propagation (and have the same frequency)

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Properties

1/ An electromagnetic wave is propagating in the vacuum

2/ In the vacuum the wave propagates perpendicular to the plan (formed by

the E and M vectors) at a constant speed of 3.108 m/s)

3/ The propagation goes straight

N.B: When an EM passes through matter it doesnt affect its frequency but its speed and in the case of

the air the consequences are insignificant

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Forms of electromagnetic radiation like radio waves, light waves or infrared (heat) waves

have a characteristic patterns => each wave has a certain shape and length.

The distance between peaks (high points) is called wavelength.

The difference in wavelength is

the way we tell different kinds ofelectromagnetic energy apart.

What is a wavelength ?:

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Wavelength and Frequency

c = the speed of light (3x108 m/s) [m/s]

= wavelength [m]

f = frequency [1/s]

c = * f

Example :

An EM wave with a frequency of 5 GHz has a wavelength of 6 cm

light needs 8 sec from the sun to the earth and 1.3 sec from moon to earth

m/s = m x 1/s

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Power of tens

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Do you know how to play with units?

How much is 1000 nm in meter ?

How much is 12 Ghz in MHz ?

How much is 9 nm in cm ? What is the speed of light in km/s

What is the wavelength of a 2 MHz frequency in nanometer ?

What is the frequency in Mhz of a 25 nm wavelength ?

How much is 10 m in power of ten? And so in nm?

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Wavelength and Frequency c = the speed of light (3x108 m/s)

= wavelength [m]f = frequency [1/s]c = * f

Exercice 1:

GSM frequencies are around 900 MHz, What is the range of the corresponding

wavelength?

Exercice 2:

The Pre-Wimax antenna we will use have their frequency around 2.4 GHZ, what

is the corresponding wavelength?

Exercice 3:

What are the corresponding frequencies of the following wavelength:

25 cm ; 0,05m ; 1mm ; 1 cm ; 1m ?

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Polarisation, what is this?

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What are Radio Waves ?

The electromagnetic spectrum

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c = * f

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Electromagnetic radiation is made when an atom absorbs energy.

What makes electromagnetic radiation (1/3) ?

2 When the electron returns to its original position, an electromagnetic wave

is produced.

Depending on the kind of atom and the amount of energy, this electromagnetic

radiation can take the form of heat, light, ultraviolet, or other electromagnetic

waves.

1 The absorbed energy causes one or more electrons to change their locale

within the atom.

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There are several ways of causing atoms to absorb energy:


One way is to excite the atoms with electrical energy (ex : neon).

The electricity we put through the neon tubes will excite or add energy

to the neon atoms.

The electrons don't like to be in the high energy state and will fall back down

into the low energy state giving off radiation which we see as light.

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When a direct electrical current is applied to a wire the current flow builds an

electromagnetic field around the wire

=> This field sends a wave outward from the wire.

When the current is removed, the field collapses which again sends a wave.If the current is applied and removed over and over for a period of time,

=> a series of waves is propagated at a discrete frequency.

If the current changes polarity, or direction repeatedly, that could make waves, too.

FYI: Other kinds of electromagnetic radiation, including radio waves, are made by natural processes

such as the nuclear reactions in a star.


This phenomenon is the basis ofelectromagnetivity and basically describes

how radio waves are created within transmitters.

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Radio waves almost always travel through space in a straight line.

There are two exceptions :

How does reflection affects radio waves?

- Radio waves are pulled and turn slightly because of gravity when they pass

by large masses

- Radio waves can be reflected by certain substances, like the way that light is

reflected by a mirror

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Reflectance is used to great advantage in designing the antennas that collect radio signals.

FYI:

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Atmospheric refraction

Due to variations in the density of

the atmosphere, electromagnetic

radiation is refracted according to the

varying refractive index with height

Variations decreases linearly with

height under standard conditions.

As a result, the wave gradually curves

until, if the wavelength and angle arecorrect, the signal bends back toward

the earth

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= Because a signal's strength gets weaker very quickly as distance increases.

Mathematically, it weakens by the square of the distance (d2) from the starting point.

That means that if you are twice as far away the signal is only one-fourth as strong.

ex: 2 km = 0.5 dBm

4 km = 0.25 dBm

Why do communications get harder at greater distances (1/2) ?

= >This is caused by how radio waves behave, they start out close to one another

when they are first projected by the antennae, and then spread out as they get farther

from their source.

This relationship is known as the inverse-square law of electromagnetic propagation.

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III. What is a frequency ?

What is a decibel (1/4) ?

The decibel (dB) is a measure of attenuation, gain, level of reception

db = 10 log10(P2/P1)

P1 is the initial power, P2 is the final power

3 dB is a decline to half of a signals original power

1/2 = 3 dB (P2 = P1/2)

1/4 = 6 db

1/8 = 9 dB

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10 dB is a decline to one tenth of a signals original power

1/10 = 10 dB (P2 = P1/10)

1/100 = 20 dB

1/1000 = 30dB

The decibel is a logarithmic scale

Small increases in the number of decibels correspond to a large

decrease in signal strength

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dBVV1

100m

10m

1m

100

10

1

100n

10n

dB = 20 log10 Vout/Vin

dBV = decibel volt = 20 log10 V

1V = 10-6

V


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Exercise:

1 Watt = ____mW = __ dBm

dBmW1000

100

10

1

100m

10mW

1mW

100

10

AttentionIn Power:

dBm = decibel milliwatt = 10 log10 (P*103)


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Why do communications get harder at greater distances (2/2)?

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We are talking about

density !!!!

The energy or intensity decreases by a factor of 14 as the distance r is doubled,

or measured in dB it would decrease by 6 dB

Exercise:

- If at 5 km I receive a signal at 0 dB what will it be at 25 km?

- I receive a signal at a level of 5 dB at 2km where will I receive 11 dB and -1 dB?

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There are two common ways to put information in a radio wave:

- A.M that stands for Amplitude modulation

- F.M that stands for Frequency Modulation

It is important to know that radio waves have very regular patterns,generally

they keep the same amplitude or frequency all the time.

How is data put on radio waves (1/3) ?

Amplitude is the "height" of the radio wave, frequency is how close the waves are

to each other.

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For A.M = information is put into a radio wave by varying the amplitude

For example: if all we wanted to do was send 1's and 0's, we could have just

two different levels of amplitude = 1 being high, 0 being low.


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For F.M = This time the amplitude is kept constant, it is the frequency that is varied.

For example: if all we wanted to do was send 1's and 0's, we could have just two different

levels of amplitude = 1 being small wavelength frequencies, 0 long wavelength.


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Bandwidth = Total range of frequency required to pass a specific signal that has been

modulated to carry data without distortion or loss of data.

N.B: Transmitters and receivers have bandwidths. The "wider" the receiver's bandwidth is,

the more information it can receive on different frequencies.

What is bandwidth ?

The ideal bandwidth allows the signal to pass under conditions of maximum

AM or FM adjustment :

- Too narrow a bandwidth will result in loss of data.

- Too wide a bandwidth will pass excessive noise.

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Module I: Wireless Basic Concept


What problems are there besides noise?

One characteristic = Some frequencies can't pass through certain substances.

Our atmosphere is made up of many different layers each made up of different substances.

There are a few "windows" in our atmosphere's absorption that allow some

electromagnetic radiation to get through.

Some of these windows are what make it possible to see visible light and receive

radio frequencies and we are rarely alone to use them!

=> Most of the electromagnetic spectrum is absorbed by our atmosphere.

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Microwave: 2.45GHz

Main Effect at 2Ghz: Heating

What are EM effects?

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How are frequency and wavelength related ?

Electromagnetic waves always travel at the same speed

= m.s-1

/ Hz = m.s-1

/ s-1

= m

= m.s-1/ m = s-1 = Hz

Wavelength =Speed of light

Frequency of oscillation

Frequency of oscillation = Speed of light

Wavelength

Any electromagnetic wave's frequency multiplied by its wavelength equals

the speed of light.

C = SPEED OF LIGHT = 299 792 km per second (3 .108m.s-1)

FREQUENCY OF OSCILLATION x WAVELENGTH = SPEED OF LIGHT

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IV. What is a frequency ?

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Example :

If the time it takes for a wave

to pass is 1/100 of second,

the frequency is 100 per second= 100Hz

If it takes 1/2 second,

the frequency is 2 per second

= 2 Hz

Frequency = Number of waves that pass a fixed place in a given amount of time

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Frequency Measurement = Hertz unit

From 19th-century German physicist Heinrich Rudolf Hertz

Hertz measurement (Hz) = Number of waves that pass by per second.

For example :

an "A" note on a violin string vibrates at about 440 Hz (440 vibrations per second).

Hertz Unit

F (Hz) = 1 / T

(T is the period between peaks (high points) =period of wavelength)

=>1Hz = 1/S

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We have seen:

f

c

c = 300,000 km/s,

f = frequency in Hertz,

= Wavelength in m

Antenna = /4

UMTS: 1900 MHz

= ? cml /4 = ? cm

Exercise

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120 dBm

100

80

60

40

20

3 MHz

100m

30 MHz

10m

300 MHz

1m

3 GHz

10 cm

30 GHz

1 cm

300 GHz

1 mm

TV VHF

Amateurs

Amateurs

GSM

TV UHF

Military radarSatellites

Oven

Tl

page

DECT

TFTS

0

1W

1mW

1MW

1KW

1GWMeteo radar?

Panorama

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QuickTime et un


Standards

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oneChoice of Frequency (1/3):

1 The lower frequency, the further it goes

2 The lower frequency, the better it goes through

and around things

3 The higher frequency, the more data it can transport

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one

Choice of Frequency (2/3):

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oneChoice of Frequency (3/3):

FSL(dB) = 20log10(d) + 20log10(f) + K

FSL= Free Space Loss

d = distance

f = frequency

K = constant depending on the units used for d and f

Power loss is proportional to the square of the distance and proportional

to the square of the frequency

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II&III. QUIZZ

oneQUIZZ 1:

Which one of those are EM energy

o sound

o wave of the sea

o radio wave

o light

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II&III. QUIZZ

oneQUIZZ 2:

How can we differenciate types of EM wave

o Using its frequency

o Its amplitude

o Its wavelength

o its name

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II&III. QUIZZ

oneQUIZZ 3:

What is changed when a EM wave passes through matter

o Its frequency

o Its amplitude

o Its shape

o Its speed

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II&III. QUIZZ

oneQUIZZ 4:

What is the speed of light

o 3.108 km/s

o 3.105 km/s

o 3.108 m/s

o 3.105 km/s

o 3.1010 cm/s

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II&III. QUIZZ

oneQUIZZ 5:

EM wave Properties in the vacuum are

o Different in the upper atmosphere

o Same as in the upper atmosphereo Same as in the air (staying in the lowest atmosphere)

o Different as in the air (staying in the lowest atmosphere)

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II&III. QUIZZ

oneQUIZZ 6:

Short wavelength correspond to

o High frequencieso Low frequencies

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II&III. QUIZZ

oneQUIZZ 7:

1 GHz is equal to

o 109 Hz

o 106 Hzo 106 kHz

o Giant hertz

o Giga hertz

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II&III. QUIZZ

oneQUIZZ 8:

When the wavelength increases the frequency decreases

o Falseo Wrong

o True

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II&III. QUIZZ

oneQUIZZ 9:

1/Could you explain me how to create an EM ?

2/ Explain me the reflection effect, how does it work ?

Give me an example of one application ?

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II&III. QUIZZ

oneQUIZZ 10:

From 2 km to 16 km the power in dB

o Is Doubled

o Is multiplied by 4

o Has been divided by a factor of 2

o Has been divided by a factor of 4

& Q

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II&III. QUIZZ

oneQUIZZ 11:

A gain of 3dB increase the power by a factor of

o 2

o 4o 6

And 10dB

o by 10o 100

M d l 1 Wi l B i C

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IV. Propagation, Attenuation and

Interference

II Wh i El i W ?

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EM waves effects (2/2)

chap 2 & 3 em & freq

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