GUIDED AND UNGUIDED

TRANSMISSION MEDIUM

TRANSMUSSION MEDIUM

GUIDED

METALLIC CABLE

TWISTED PAIR

STP UTP

FIBER OPTIC

UNGUIDED

SATELLITE

COAXIAL CABLE

1

UNSHIELDED TWISTED PAIR (UTP) CABLE

2

• cable has four pairs of wires

• not surrounded by any shielding

• Each pair is twisted with a different

number of twists per inch to help

eliminate interference from adjacent pairs

and other electrical devices

• primary wire type for telephone usage

and is very common for computer

networking

• Connector-RJ45 (looks like a large

telephone style connector)

3

• Disadvantage: susceptible to radio and

electrical frequency interference

4

SHIELDED TWISTED PAIR (STP) CABLE

5

• suitable for environments with electrical

interference

• includes metal shielding over each

individual pair of copper wires

• protects cable from external EMI

(electromagnetic interferences

• extra shielding can make the cables quite

bulky

6

COAXIAL CABLE

7

• often used as a high-frequency

transmission line to carry a high-

frequency or broadband signal

• may also be used for frequencies as low

as audio frequency.

• Example: connection to TV antenna

• Bandwitdh-400 MHz, data speed -

10Mbps

8

•basic construction: -centre core: as a conductor, carry the signal

dielectric insulator: provides insulation between the centre conductor and braided metal shield -metal shield: block any outside interference from fluorescent lights, motors, and other computers

-plastic jacket: give protection to cable 9

• advantages: is highly resistant to signal

interference, can support greater cable

lengths between network devices

• disadvantage: expensive

• types of coaxial cabling are thick coaxial

and thin coaxial.

10

Connector-BNC (Bayone Neill Concelman)

(T-connector, barrel connector, terminator , etc)

11

FIBER OPTIC CABLE

• transmit light to eliminating the problem

of electrical interference

• transmit signal over long distances,

greater speed, difficult to install

• use ST connector-similar to BNC

12

3 LAYER: • carries the light CENTRE CORE

• covering the core CLADDING

• protection for cladding

COATING 13

CHARACTE

RISTIC

FIBER

OPTIC

CABLE

CONVENTION

AL

ELECTRICAL

CABLE

ELECTROMA

GNETIC

FIELD

ҳ

√

cost For long

term,low cost

High cost

14

CHARACTE

RISTIC

FIBER

OPTIC

CABLE

CONVENTIO

NAL

ELECTRICA

L CABLE

LOSS 0.1-0.6 db/km 18 dB/km

BANDWIDTH >1GHz 600 MHz for

coaxial cable

WEIGHT 40 km per 1 kg 0.7 km per 1

kg

DIAMETER 0.125 mm 9.5 mm

INFORMATIO

N QUALITY

Very good noise

15

ELEMENTS IN AN OPTICAL FIBER OPTIC

COMMUNICATION

• The main elements are:

• 1. DRIVING CIRCUITRY

- Electrical interface between the input

circuitry and the light source

- To drive the light source

2. LIGHT SOURCE

- To convert electrical energy to optical

energy

- Optical energy proportional to the amount

of drive current

16

• 2 types-Light Emitting Diodes (LED) and

Laser

3. LIGHT SOURCE TO FIBER COUPLER

-is an interface to couple the light emitted

by the source into the optical fiber optic

4. FIBER TO DETECTOR COUPLER

-is an interface between fiber and light

detector to couple as much light as

possible from the fiber cable into the light

detector

17

• 5. LIGHT DETECTOR

-Convert light energy to current

-2 types – PIN (p- type –intrinsic-n-type)

and APD (avalanche photodiode)

18

PROPAGATION MODE

• To show how the light is propagated

along the fiber

• Mode means path

• One path-single/monomode

• More than one path – multimode

• 3 types:

• -SINGLE MODE STEP INDEX

• MULTIMODE STEP INDEX

• MULTIMODE GRADED INDEX

19

20

SINGLE MODE STEP

INDEX

• Has a very small core diamater, 8µm to

12µm

• Only a single path of light

• All light rays follow approximately the

same path down the cable

• Take same amount of time to travel the

length of the cable

21

MULTIMODE STEP INDEX

• The centre core is larger

• Has large light to fiber aperture and

allows more light to enter the cable

• Light rays propagated down the cable in

a zig-zag pattern, resulting many paths

• All light rays do not follow the same

path, with different propagation time

22

MULTIMODE GRADED INDEX

• Is characterised by a central core

• Has a refractive index that is non

uniform; max at centre and decreases

gradually toward the side of the cable

• light is propagated down the fiber by

refraction

• Continuous bending of the light rays, at

many different angles

• All the light rays arrive at the end point at

almost the same time 23

APPLICATIONS OF FIBER-OPTIC

• Their primary use is in long-distance

telephone systems ,cable TV system and

internet

• some applications

• -CCTV

• --Secure communications systems at

military bases.

• Computer networks, wide area and local

area.

• -

24

• - Shipboard communications.

-Aircraft communications/ controls.

-Interconnection of measuring and

monitoring instruments in plants and

laboratories.

-Data acquisition and control signal

communications in industrial process control

systems.

25

• Nuclear plant instrumentation.

• -College campus communication.

• -Utilities ( electrical , gas, and so on)

station communications.

• -Cable TV systems replacing coaxial

cable.

26

WAVEGUIDE

• waveguide is a hollow metal tube

designed to carry microwave energy

(>1GHz) from one place to another

• carry energy between pieces of equipment

or over longer distances to carry

transmitter power to an antenna or

microwave signals from an antenna to a

receiver

• Made from copper,aluminium or brass

(long rectangular or circular pipes) 27

28

29

•RF energy is inside the waveguide, it travels along inside, • reflecting off the inside walls as it proceeds

30

• inside surface of the waveguide have a

low electrical resistance- plated with

excellent (and expensive) conductors,

such as silver or gold.

• plating need not be very thick because RF

currents will only flow along the "skin" of

the wall.

31

MICROSTRIP

32

33

• For high frequency (300 MHz to

3000MHz)

• Can be used to construct transmission

lines, inductor,capacitor,filter etc

• A flat conductor separated from a ground

plane by an insulating dielectric material

• The ground plane serves as the circuit

common point (connected to ground) –

must be at least 10 time wider than top

conductor

34

SATELLITE

COMMUNICATION

• Satellite system consist:

-transponder (radio repeater in the sky)

-a ground base station to control its

operation

-a user network of earth stations that

provide the facilities for transmission and

reception

35

SATELLITE

COMMUNICATION

36

SATELLITE

COMMUNICATION

37

• Satellite receive a signal from the ground

station

• Do the amplification and frequency

translation

• Broadcast it to earth stations that are able

to receive transmission

• A satellite begin at a single earth station,

passes through the satellite and ends at

one or more earth station • Figure 4.13 page 108

38

• Satellite transponder

- pick up the transmitted signal from the

transmitter on the earth

-to amplify the signal

-to translate the carrier frequency to another

frequency

-to retransmit the amplified signal to the

receiver on the earth

39

• Uplink- is the path of the satellite signal

from the earth transmitter to the receiver

of the satellite

• Downlink-is the path of the satellite

signal from the satellite transmitter to the

receiver on the earth

• Uplink and downlink use different carrier

frequencies to avoid interference

• Uplink-6 GHz, Downlink – 4 GHz 40

Satellite frequency bands

• Use microwave frequency spectrum

• Designed by a letter of the alphabet

41

Satellite frequency bands

42

Satellite frequency bands

43

Advantages of satellite system

• Can access to wide geographical area.

• Wide bandwidth.

• High reliability.

• Distance insensitive cost.

• Rapid installation and low cost per added

site.

44

LIMITATION OF SATELLITE

COMMUNICATION

• Signal Latency -the delay between

requesting data and the receipt of a

response.

• Rain Fade -are affected by moisture and

various forms of precipitation (such as

rain or snow) in the signal path between

end users or ground stations and the

satellite being utilized.

45

• High equipment cost.

• Line of sight -Typically a completely

clear line of sight between the dish and

the satellite is required for the system to

work

- similarly impacted by the presence of

trees and other vegetation in the path

of the signal

46

ANTENNA

• Antenna- transducer (RF electrical

current to electromagnetic wave)

designed to transmit/receive radio wave.

• Has a high gain and narrow beam.

47

TYPES OF ANTENNA

1. Omnidirectional

• all directions..

• rural areas.

• Used only one element.

• circular shape area, base station placed in

the middle

Coverage area

RBS

48

• Directional(Microwave dish)

• certain direction.

• Three antennas needed in 1200

arrangement, close to each other.

• urban areas which support a lot of

subscriber.

Sel

antenna

49

ANTENNA PROPAGATION

• Size an antenna is inversely proportional

to frequency

• Small antenna – radiate high frequency.

• Large antenna – radiate low frequency.

50

• Electromagnetic wave travelling within

atmosphere called terrestrial wave

• Communication between two or more

points on earth called terrestrial radio

communication

• There are 3 modes of propagation

possible between Electromagnetic wave

within Earth atmosphere :

1. Ground wave.

2. Space wave.

3. Sky wave.

51

52

53

54

55

GROUND WAVE

• Ground Waves are radio waves that

follow the curvature of the earth

• Affected by the ground’s properties

• Because ground is not a perfect electrical

conductor, ground waves are attenuated

as they follow the earth’s surface.

• This effect is more pronounced at higher

frequencies, limiting the usefulness of

ground wave propagation to frequencies

below 2 MHz. 56

57

SPACE WAVE

PROPAGATION

• Include both direct wave and ground

reflected wave

58

• Ground reflected wave are wave reflected

by Earth surface as they propagate

between the transmit and receive antenna

• direct waves, are radio waves that travel

directly from the transmitting antenna to

the receiving antenna

• the two antennas must be able to “see”

each other; that is there must be a line of

sight path between them

59

SKY WAVES

• Are radiated towards the sky

• They are either reflected or refracted back

to earth by the ionosphere

60

61

• Sometimes called ionospheric

propagation

• Ionosphere

-region of space located approximately 50

km to 400 km above earth’s space

-upper portion of earth’s atmosphere

62

63

Q & A

session

THE END 64