Transmission Mediums ( Guided / Unguided ) Part 2

 

Wireless (Unguided) Transmission Media :

• A wave can be described as a disturbance that travels through a medium from one location to another location .
• A wave is a transfer of energy , usually through a form of matter called a medium .
• There are special type of wave that can travel without a medium , called electromagnetic waves ( Also called WEM waves) , which are waves like radio waves and microwaves.
• The electromagnetic spectrum describes a wide range of different electromagnetic waves .

A little part of electromagnetic spectrum can be used for wireless transmission .

1- Radio Waves Transmission 

• Radio waves are EM waves that have wavelengths between 1 millimeter and 100 kilometers ( 0r 300GHZ and 3KHZ in frequency).
• Radio frequency is easy to generate because its has large wavelength and can travel long distance.
• Radio waves are generated by radio transmission and received by radio receivers.
• Radio stations transmit radio waves using transmitters , which are received by the receiver installed in our devices .Both transmitters and receivers use antenna .
• It can penetrate walls easily , so these waves are widely used for communication both indoors and outdoors .

• Radio waves are omnidirectional means they travel in all the directions from the source.
• When an antenna transmits radio waves , they are propagated in all directions.
• A sending antenna send waves that can be received by any receiving antenna . The omnidirectional property has disadvantage too . The radio waves transmitted by one antenna are susceptible to interference by another antenna that may send signal using the same frequency or band.
• It is used Mobile , AM/FM radio , television.

2- Microwaves Transmission :

• Microwaves are a type waves with high frequencies . It can be classified as a subclass of radio waves . The frequency of microwaves lies in the 300MHZ to 300GHZ.
• Unlike radio waves , microwaves are unidirectional , in which the sending and receiving antennas need to be aligned.
• Microwaves are widely used for point - to - point communications because their small wavelength , which means that the signal is focused in to a narrow beam . Additionally , each antenna must be within line of sight of the next antenna.

• Microwaves have higher frequencies and do not penetrate wall like obstacles.
• It is used for satellite communication , navigation , radar , remote sensing and other short distance communication systems .

3- Infrared Waves Transmission :

• Infrared signals have frequencies between 300GHZ to 400GHZ . They are used for short range communication.
• Infrared waves are used for very short distance communication like TV remote , wireless speakers , automatic doors , hand held devices etc.

• Infrared waves having high frequencies prevents interference b/w one system to another.
• Infrared signals have high frequencies and cannot penetrate walls . Due to its short range communication system , the use of an infrared communication system in one room will not be affected by the use of another system in the next room . This is why using an infrared TV remote control in our home will not interfere with the use of our neighbor's infrared TV remote control.

The disadvantages of using Infrared

Infrared signals cannot be used for long distance communication . In addition , we cannot use infrared waves outside a building because sun's rays contain infrared waves that can interfere with communication

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Transmission Mediums ( Guided / Unguided ) Part 1

Transmission Medium :

• Transmission medium is the way in which data is transmitted from one place to another .

• It provide a pathway over which the message can travel from sender tp receiver .

• Each of the message can be sent in the form of data by converting them into binary digits.

• These binary digits are then encoded into a signal that can be transmitted over the appropriate medium. 

Wired / Guided Transmission Media :

• Guided Transmission Media are the cables that are tangible or having physical existence

• Bounded transmission means having connectivity between source and destination using cables or wires . The signals having to travel through this channel i.e.physical media.

Twisted Pair Cable :

A twisted pair cable is a pair of copper wires .

Copper wires are the most common wires used for transmitting signals because of good performance at low costs .

A twisted pair consists of two conductors each with its own plastic insulation , twisted together to form a signal media .

Out of these two wires , only one carries actual signal and another is used for ground reference.

To identify every cable , these cables are color coded .

This twists between wires are helpful in reducing noise ( electo-magnetic interference ) and crosstalk.

This type of cables is used in telephone lines tp provide voice and data channels .

The two types of twisted pairs are :

Unshielded Twisted Pair ( UTP ) :

• UTP is more common.
• UTP cost less than STP and easily available due to its many use.
• Due to its low cost , UTP cabling is used extensively for Local Area Networks (LANs) and telephone connections.
• UTP cables consists of 2 or 4 pairs of twisted cables.
• Cable with 2 pair use RJ11 connector and 4 pair cable use RJ45 connector.

RJ-45 connectors is used with Ethernet cables in computer networking.

RJ-11 connectors is used in connecting telephone units.

Shielded Twisted Pair ( STP ) :

• This type of cable has a metal foilcovering which encases each pair of insulator connectors.
• Electromagnetic noise penetration is prevented by metal casing . Shielding also eliminates crosstalk.
• It is similar to UTP but has a mesh shielding that is protect itfrom EMI which allows for higher transmission rate .
• It is more expensive than coaxial and UTP.

Coaxial Cable :

• Coaxial cables are copper cables with better shielding than twisted pair cables , so that transmitted signals may travel longer distances at higher speeds.
• The shield minimizes electrical and radio frequency interference.
• Coaxial cabling is the primary type of cabling used by the cable television industry and is also widely used for computer networks such as Ethernet. 

• Coaxial cable has two wires of copper .
• The core/inner copper wire in center and is made of solid conductor . It is enclosed in an insulating sheath.
• The second/outer copper wire is wrapped around , and is used to protect from external electromagnetic interference ( Noise ).
• This all is covered by plastic cover used to protect the inner layers from physical damage such as fire or water.

Fiber Optics Cable

• A fiber Optic cable is made of high quality of thin glass or plastic and iis used to transfer digital data signals in the form of light up to distance of thousand of miles.

• Fiber optic cables are not affected by electromagnetic interference , so noise and distortion is very less.
• Fiber optic cables carry communication signals using pulses of light generated by small lasers or light emitting diodes ( LEDs ).
• The cable consists of one or more strands of glass , each only slightly thicker than a human hair . The centre of each strand is called the core , which provides the Pathway for light to travel. The core is surrounding by a layer of glass called Cladding that reflects light inwards to avoid loss of signal and allow the light to pass through bends in the cable . No light escapes the glass core because of this reflective cladding .

Advantages of Optical Fiber :

• Fiber optic cables have a much high bandwidth ( BW ) than metal cables . This means that they can carry more data 
• Smaller size and lighter weight .
• Low attenuation .
• Not affected electromagnetic interference .
• Signals carrying data can travel long distance without weakening.
• Suitable for industrial and noisy areas.

Disadvantages of Optical Fibre :

• Optical fibre cables are expensive.
• Difficult to install .
• Maintenance is expensive and difficult.

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Microwave Transmission Basics

What is Microwave ? 

• Microwave ( MW ) are a form of electromagnetic radiation with wavelengths ranging from 1m to 1mm
• Frequencies between 300MHZ to 300GHZ

 Microwave Transmission :

• Microwave transmission is the transmission of information ( Voice , data , television or radio signals ) by microwave radio waves.
• Microwaves are widely used for PPP ( Point - to -Point ) communications because their small wavelength allows conveniently sized antennas to direct them in narrow beams , which can be pointed directly at the receiving antenna.

Microwave Link / Hop

• The connection of two fixed microwave sites via a line of  light (LOS) path.
• It is called Hop

Microwave Key Parameters :

• Hertz ( HZ ) :

A measurement of a signal's electromagnetic frequency , expressed as a number of cycles per second.

KHZ : Kilohertz , MHZ : Megahertz , GHZ : Gigahertz , THZ : Terahertz 

• Frequency :

The rate of the wave's oscillation , measured in hertz ( HZ )

• Amplitude :

The strength of power level ofthe wave

• Phase :

The particular point in the cycle of a waveform , measured in degrees 

• Polarization 

The orientation of the electric field driving the wave 

Line Of Sight ( LOS )

It is a type of propagation that can transmit and receive data only where transmit and receive stations are in view of each other without any obstacles between them .

Examples are FM radio , Microwave and satellite transmission 

Antennas :

Antennas are devices that radiate or receive EM waves of certain frequencies 

Microwave Antenna :

An antenna designed to radiate and receive microwave frequencies , therefore is called a microwave antenna .

Waveguide :

A metallic physical transmission medium & waves propagate along it .

Microwave energy travels through guided media is called waveguide .

Waveguide Types :

Rectangular Waveguide

Circular waveguide 

Elliptical waveguide 

Corrugated Waveguide 

Properties of Microwave links :

Involve LOS communication technology.

Affected greatly by environmental constraints including rain fading .

Have very limited penetration capabilities through obstacles such as hills , building and tress .

Signals can be degraded during solar proton events.

Fading :

Loss in signal strength a cross a link caused by atmospheric disturbance link rain or snow that can scatter microwave signals .

The lower frequency microwave bands offer the greatest possible distance - theoretically allowing for links in excess of 50 KM

Microwave Frequencies :

Microwave Frequency & it's application 

Low Frequency VS High Frequency 

The lower frequency bands offer the greatest possible distance - theoretically allowing for links in excess of 50 KM.

Adaptive Transmit Power Control ( ATPC )

ATPC dynamically adjusts power levels to compensate for any link impediments .

Adaptive Modulation :

Is used dynamically switch modulation schemes according to the prevailing channel conditions .

Typical modulation schemes selected for adaptive modulation are 4QAM , 16QAM , 64QAM , 128QAM , 256QAM , 512QAM and 1024QAM

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