topic 1-the electromagnetic spectrum

7/29/2019 Topic 1-The Electromagnetic Spectrum

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Telecommunication engineering Principles

Chapter 1

The Electromagnetic Spectrum

Ade Syaheda Wani Binti Marzuki

Department of Electronic Engineering

Semester 1, Session 2009/2010


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Outlines

1.1 Modern Communications Systems

1.2 Electromagnetic Waves and Energy

1.3 Electromagnetic Spectrum and Allocations1.4 Bandwidth and Information Capacity

1.5 Simplex, duplex and half-duplex systems

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PART 1.1

Modern

Communications Systems



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What iscommunication?

1.1 Introduction to modern

communication systems


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Definition:Communication:

A process of transferring information or

data from one source to another.

Data:

Can be text, image, video, voice and etc

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Definition:

Communication system:

A set of electronic equipments for

transmitting and receiving information inunderstandable format.



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Whycommunication is

important?




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Importance of communication:

Send messages over great distances easily and

reliably

Send large amount of data quickly from onepoint to another

Example of modern communication:

Hand-held radios Satellite dish antenna

Commercial radio/ tv station

RadarKNL2833

Telecommunication Engineering Principles


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What do we need

for anycommunication to

occur



1 1


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Basic requirements:

At least 2 endpoints

Source;

Data; Medium of transmission;

Receiver.

Both party must agree upon Coding

Meaning

Modulation used



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PART 1.2

Electromagnetic

Waves and Energy


1 2 El t ti W


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1.2 Electromagnetic Waves

and Energy

Information sent from one point to another inform ofelectromagnetic energy

Various mode of electromagnetic energy:

same basic law

of physic apply


Voltage/ current through

wires

Radio emissions through

air or the vacuum of space

Light

WavelengthVelocity

frequency

1 2 El t ti W


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and Energy

Wavelength Distance between peaks of the

oscillations of the energy waves

Also equivalent to the distance travelled in

time to complete one cycle

Velocity The speed at which the energy travels

through the wire, air, vacuum or optical

fiber

Frequency Number of oscillations or cycles per

secondKNL2833


f

vc

Relationship:

1 2 El t ti W


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and Energy

Propagation velocity Speed at which a wave travels depend on the

substance or medium through which it is

travelling

Fastest propagation velocity in VACUUM!,


smc /103 8

1 2 El t ti W


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and Energy

Try this!Example 1.1

What is the wavelength in a vacuum for a

frequency of 1 million Hertz?

Hint: useKNL2833

Telecommunication Engineering Principlesf

v

c

1 2 El t ti W


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and Energy


What is the frequency when the measured

wavelength is 6 m?

Hint: useKNL2833

Telecommunication Engineering Principlesf

v

c

1 2 El t ti W


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and Energy

Propagation velocity The propagation velocity is less in any medium

other than vacuum.

In air: 95-98% of the value in vacuum

In wire: 60-85% of the value in vacuum

(depending on wire type. Construction and

insulation)

e.g: common type of cable used for cable TV

has propagation velocity of 75% ofc.


1 2 El t ti W


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and Energy

The frequency of communications system isdetermined by the transmitter circuitry.

It is designed to have specific value or range of

values.

e.g:

A standard AM broadcast radio signal at

1,000,000 Hz in the vacuum of space haswavelength of:


mHz

sm 28

103000,000,1

/103

1 2 El t ti W


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and Energy

e.g:A TV broadcast signal for channel 11 uses a

frequency of 200 MHz. The corresponding

wavelength in vacuum is:


mHz

sm5.1

102

/1036

8

1 2 Electromagnetic Wa es


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and Energy


A signal is normally sent theough vacuum,

at a frequency 60 million Hz. However, it is

also broadcast through air, with propagation

factor = 0.98 of c. What is the wavelength in

(a) vacuum, and (b) air?


1 2 Electromagnetic Waves


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and Energy


The same signal is now sent through a

cable, with propagating factor of 0.69 of c.

What is the velocity? What is the

wavelength?



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PART 1.3

The Electromagnetic Spectrum

And Allocations


1 3 The Electromagnetic


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1.3 The Electromagnetic

Spectrum and Allocations

Electromagnetic Spectrum Total span of frequencies and corresponding

wavelengths used in communication systems


1 3 The Electromagnetic


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1.3 The Electromagnetic

Spectrum and Allocations

Electromagnetic Spectrum Divided into different bands, each with a name

and boundaries.

Each band is used for many communications

services.

Frequency assigned/allocation by ITU

(International Telecommunications Union) to

avoid interference.



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PART 1.4

Bandwidth and Information

Capacity


1 4 Bandwidth and


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1.4 Bandwidth and

Information Capacity

Bandwidth, B Span of frequencies within the spectrum is

occupied by a signal and used by the signal to

convey information

Issues in sending any information Minimum Bandwidth

Bandwidth Required

Bandwidth available in the higher-frequencyband is much greater that in lower-frequency

bands


1 4 Bandwidth and


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1.4 Bandwidth and


Information Capacity, C Information capacity of a communication

channel is related to bandwidth, signal power,

and noise in the channel.

Shannons formula:

Where:

C is in bits/second

B is in Hz

signal power and noise power in WattKNL2833Telecommunication Engineering Principles

powernoise

powersignalbandwidthC 1log2

1 4 Bandwidth and


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1.4 Bandwidth and


Example:Suppose a communications link is using a

transmitter of 10 W power, and there is 1W

of noise power in the same link. The channel

capacity is therefore:

To increase the information capacity, we have

to increase the bandwidth first.


sbitsC /3459

1

101log1000 2

1 4 Bandwidth and


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1.4 Bandwidth and


Example:Suppose that 10,000bits/s must be sent so

that the user does not have to wait too long

for the critical data, and the system has 100

W of signal power versus 10 W of noise

power. The bandwidth required is


Hz

noisesignal

powersignal

C

B 2890)1(log 2

1 4 Bandwidth and


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1.4 Bandwidth and



What bandwidth is needed by Shannons

Theory, to support a capacity of 20,000 bits/s

when the ratio of signal power to noise ratio

is 100?

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PART 1.5

Simplex, Duplex and Half-Duplex

System

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1 5 Simplex Duplex and


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1.5 Simplex, Duplex and

Half-Duplex System

Simplex System A system that is capable to send the information

in one direction only

No provision for sending in reverse direction

e.g: Broadcast radio, TV

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Half-Duplex System

Duplex or Full Duplex System A system that is capable to send the information

in two direction at same time

Both party can receive or transmit at same time,the message travels independent of each other.

Require twice the bandwidth, number of wires or

number of signal channels

e.g: phone call

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Half-Duplex System

Half Duplex System A system that is capable to send the information

in both direction, but in one direction at a time

Both party can only receive or transmit at onetime

Use same the bandwidth, number of wires or

number of signal channels

e.g: walkie talkie, push to talk

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topic 1-the electromagnetic spectrum

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