TRANSMISSION LINE

PRINCIPLES OF TRANSMISSION LINES

INTRODUCTION TO TRANSMISSION LINES

TRANSMISSION LINES- is a device designed to guide electrical energy from one point to another - It is used, for example, to transfer the output of energy of a transmitter to an antenna

Classes of transmission media

Guided media provide a physical path along which the signals are propagated; these include twisted pair, coaxial cable, and optical fiber

Unguided media employ an antenna for transmitting through air, vacuum, or water.

ELECTROMAGNETIC SPECTRUM

All transmission lines have two ends :

-The end of a two-wire transmission line connected to a source is ordinarily called the INPUT END

Other names include :1. GENERATOR END 2. TRANSMITTER END 3. SENDING END 4. SOURCE

All transmission lines have two ends :

-The end of a two-wire transmission line connected to a source is ordinarily called the INPUT END

Other names include :1. GENERATOR END 2. TRANSMITTER END 3. SENDING END 4. SOURCE

The other end of the line is called the OUTPUT END :

Other names include:1. RECEIVING END 2. LOAD END 3. SINK.

GUIDED MEDIA

TWISTED PAIR a. UTP- Unshielded Twisted Pair

b. STP – Shielded Twisted PairCOAXIAL LINE FIBER OPTICS

- As the name implies, the line consists of two insulated wires twisted together to form a flexible line without the use of spacers

- It is not used for transmitting high frequency because of the high dielectric losses that occur in the rubber insulation

- When the line is wet, the losses increase greatly.

Twisted-Pair Cable

-Each pair of copper wire is twisted together and is encased in a unique color-coded plastic jacket for insulation - An outer jacket is put encasing all the twisted pair into one single bundle that consists of all the pairs for effective transmission of data

-It was invented by Alexander Graham Bell and he was granted US patent 244,426 Telephone-circuit for the invention in 1881

Unshielded Twisted-Pair (UTP) Cable: • Unshielded Twisted-Pair (UTP) Cable is

the most common type of telecommunication medium in use today.

• Frequency range is suitable for transmitting both data and voice.

• T.P consists of two conductors, each with its own colored plastic insulation.

Advantages of UTP: • It is cheaper than other communication

media. • It is easy to install and repair. • It provides good data transmission in short

distance networks.

Disadvantages of UTP: Disadvantages of UTP: It is more susceptible to crosstalkIt is more susceptible to crosstalk It is not suitable for outdoor use and long It is not suitable for outdoor use and long

distance networks. distance networks.

Shielded Twisted Pair

-It is similar to unshielded twisted pair cable except it has better insulation against signal interference

- Each pair of wire is wrapped in metallic foil to further reduce noise

- The four cables as a whole bundle are then wrapped in an overall metallic foil or braid

- With extra insulation STP reduce crosstalk (electrical noise produced by adjacent pairs) and EMI as well as RFI

Shielded Twisted Pair

Advantages of STP • It is less susceptible to EMI, RFI and crosstalk

than UTP. • It provides good data transmission in short

distance networks. • It is easy to install than other media.

Disadvantages of STP • It is more expensive than UTP. • It is relatively hard to install and repair than

UTP.

Coaxial Cable

• Coaxial Cable has a single copper conductor a plastic layer provides insulation. Coaxial has a central core conductor of solid copper enclosed in an insulating sheath.

• Carries signals of higher frequency ranges than twisted-pair cable

Categories of Coaxial cable

Optical Fiber

• Optical Fiber is made of glass or plastic and transmits signals in the form of light.

• Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair.

• It also has the capability to carry information at vastly greater speeds.

• This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is difficult to install

• Light, a form of electromagnetic energy, travels at 300,000 kilometers/second. The speed decreases as the medium through which the light travels becomes denser.

Fiber construction

Fiber-optic cable connectors

ST connector

TOS Link connector

• Optical fibers use reflection to guide light through a channel. A glass or plastic core is surrounded by a cladding of less dense glass or plastic. The difference in density of the two materials must be such that a beam of light moving through the core is reflected off the cladding instead of being refracted into it. Information is encoded onto a beam of light as a series of on-off flashes that represent 1 and 0 bits.

Optical fiber

Bending of light ray

Propagation modes

Modes of Propagation

Multimode Step-Index

• Multimode step-index uses multiple beams of light. The density of the core remains constant from the center to the edges. A beam of light moves through the constant density in a straight line until it reaches the interface of the core and the cladding. At the interface there is an abrupt change of a lower density that alters the angle of the beam's motion.

Multimode Graded-Index

• Multimode graded-index uses fiber with varying densities. Density is highest at the center of the core and decreases gradually to its lowest at the edge. Each density difference causes each beam to refract into a curve.

• Varying the refraction varies the distance each beam travels in a given period of time, resulting in different beams intersection at regular intervals. Careful placement of the receiver at one of these intersections allows the signal to be reconstructed with far greater precision

Single Mode

• Single mode uses step-index fiber and a highly focused source of light that limits beams to a small range of angles, all close to the horizontal. Propagation of different beams is almost identical and delays are negligible

Fiber types

UNGUIDED MEDIA: WIRELESSUNGUIDED MEDIA: WIRELESS

• Unguided media transport electromagnetic Unguided media transport electromagnetic waves without using a physical conductor. waves without using a physical conductor. This type of communication is often referred to This type of communication is often referred to as wireless communicationas wireless communication

UNGUIDED MEDIA: WIRELESSUNGUIDED MEDIA: WIRELESS

Propagation methods

Bands

Radio waves

• 1kHz – 1GHz• Relatively narrow (compared to microwave)• Omnidirectional (all directions)• good for long distances (sky propagation),

interference with other waves• Low data rate for digital communication.• Radio waves are used for multicast

communications, such as radio and television, and paging systems

Omnidirectional antenna

Microwaves

• 1GHz – 300GHz (wide band)• unidirectional • sending & receiving antennas should be

aligned, no interference • High data rate.• Microwaves are used for unicast

communication such as cellular telephones, satellite networks,and wireless LANs

Unidirectional antennas

Infrared

• 300GHz – 300THz• Can not penetrate walls (short range

communication, no interference)• Remote control, wireless keyboard(IrDA port,

….• Infrared signals can be used for short-range

communication in a closed area using line-of-sight propagation