chap 2 & 3 em & freq
TRANSCRIPT
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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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2Connected Schools Wireless Communication TrainingModule I: Wireless Basic Concept
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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3Connected Schools Wireless Communication TrainingModule I: Wireless Basic Concept
II. What is an Electromagnetic Wave ?
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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4Connected Schools Wireless Communication TrainingModule I: Wireless Basic Concept
II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
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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7Connected Schools Wireless Communication TrainingModule I: Wireless Basic Concept
II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
Power of tens
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II. What is an Electromagnetic Wave ?
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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10Connected Schools Wireless Communication TrainingModule I: Wireless Basic Concept
II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
Polarisation, what is this?
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II. What is an Electromagnetic Wave ?
What are Radio Waves ?
The electromagnetic spectrum
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c = * f
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II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
There are several ways of causing atoms to absorb energy:
What makes electromagnetic radiation (2/3) ?
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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II. What is an Electromagnetic Wave ?
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.
What makes electromagnetic radiation (3/3) ?
This phenomenon is the basis ofelectromagnetivity and basically describes
how radio waves are created within transmitters.
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II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
Reflectance is used to great advantage in designing the antennas that collect radio signals.
FYI:
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II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
= 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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III. What is a frequency ?
What is a decibel (2/4) ?
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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III. What is a frequency ?
dBVV1
100m
10m
1m
100
10
1
100n
10n
dB = 20 log10 Vout/Vin
dBV = decibel volt = 20 log10 V
1V = 10-6
V
What is a decibel (3/4) ?
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III. What is a frequency ?
Exercise:
1 Watt = ____mW = __ dBm
dBmW1000
100
10
1
100m
10mW
1mW
100
10
AttentionIn Power:
dBm = decibel milliwatt = 10 log10 (P*103)
What is a decibel (4/4) ?
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II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
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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II. What is an Electromagnetic Wave ?
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.
How is data put on radio waves (2/3) ?
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II. What is an Electromagnetic Wave ?
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.
How is data put on radio waves (3/3) ?
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II. What is an Electromagnetic Wave ?
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
II. What is an Electromagnetic Wave ?
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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Module I: Wireless Basic Concept
II. What is an Electromagnetic Wave ?
Microwave: 2.45GHz
Main Effect at 2Ghz: Heating
What are EM effects?
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Module I: Wireless Basic Concept
II. What is an Electromagnetic Wave ?
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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Module I: Wireless Basic Concept
Module 1: Wireless Basic Concept
IV. What is a frequency ?
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Module I: Wireless Basic Concept
III. What is a frequency ?
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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Module I: Wireless Basic Concept
III. What is a frequency ?
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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Module I: Wireless Basic Concept
III. What is a frequency ?
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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III. What is a frequency ?
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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Module I: Wireless Basic Concept
III. What is a frequency ?
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Standards
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Module I: Wireless Basic Concept
III. What is a frequency ?
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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III. What is a frequency ?
one
Choice of Frequency (2/3):
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Module I: Wireless Basic Concept
III. What is a frequency ?
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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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
II&III. QUIZZ
oneQUIZZ 6:
Short wavelength correspond to
o High frequencieso Low frequencies
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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
II&III. QUIZZ
oneQUIZZ 8:
When the wavelength increases the frequency decreases
o Falseo Wrong
o True
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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
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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Module I: Wireless Basic Concept
Module 1: Wireless Basic Concept
IV. Propagation, Attenuation and
Interference
II Wh i El i W ?
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II. What is an Electromagnetic Wave ?
EM waves effects (2/2)