This chapter discusses transmission media used for computer and data communications. It covers both guided media like twisted pair, coaxial cable, and optical fiber as well as unguided or wireless transmission using electromagnetic waves. For each medium, it describes their characteristics, applications, pros and cons. Key factors discussed include bandwidth, attenuation, interference and data rate capacity. The chapter also examines wireless transmission frequencies and antennas used for different applications. It provides details on concepts like radiation patterns, free space loss, multipath interference and how atmospheric conditions can impact wireless signals.
This document summarizes key concepts about transmission media from William Stallings' 7th edition textbook. It discusses guided media like twisted pair, coaxial cable, and optical fiber as well as unguided wireless transmission. Key factors in transmission media include bandwidth, attenuation, interference, and number of receivers. Guided media have advantages for higher data rates over longer distances while wireless has benefits for mobility but shorter range.
This chapter discusses various transmission media used for computer and data communications. It covers both guided media like twisted pair, coaxial cable, and optical fiber as well as wireless transmission methods. For each medium, it describes their characteristics such as bandwidth, attenuation, data rates, and applications. Key factors that determine the performance of different media like bandwidth, transmission impairments, and number of receivers are explained. The electromagnetic spectrum is also shown. Detailed information about technologies like antennas, radiation patterns, and wireless propagation effects are provided.
There are two main types of transmission media: guided and unguided. Guided media like twisted pair cable and coaxial cable have a physical path that signals travel along, while unguided media like wireless transmission propagate through free space. Key factors that determine the performance of a transmission medium include its bandwidth, data rate, distance capabilities, and susceptibility to interference. Common guided media include twisted pair, coaxial cable, and optical fiber, each with their own characteristics and applications for voice, data, and video transmission. Unguided or wireless transmission uses antennas to radiate signals through the air across a variety of frequency bands for applications like radio, TV, satellite, and infrared transmission.
This document discusses different types of transmission media, including their characteristics and applications. It covers both guided media like twisted pair, coaxial cable, and optical fiber, as well as unguided or wireless transmission using radio frequencies, microwaves, and satellites. Key points discussed include the factors that determine transmission quality like bandwidth and interference, the advantages of higher bandwidth and fiber optics, and how different media are suited for various uses from local networks to long-distance trunks based on their data rates and transmission distances.
Yankee Stadium implemented a wireless infrared LAN to connect cash registers to a central server for food ordering. Infrared was chosen for its low cost and ability to operate within the stadium without interfering with games. However, infrared has short range and low speeds, limiting its use to this localized application within the stadium.
The document discusses various transmission media including guided media like twisted pair, coaxial cable, and optical fiber as well as unguided media such as wireless transmission and radio. It provides details on characteristics of each medium such as data rates, distance capabilities, attenuation over frequencies, and applications. The document also reviews concepts of electromagnetic waves and provides examples of using different media for applications like local and wide area networks.
Chapter 4-Transmission Media - guided and unguided .pptxssuser32eccd
transmission medium is the physical path between transmitter and receiver
guided media – guided along a solid medium
unguided media – atmosphere, space, water
characteristics and quality determined by medium and signal
guided media - medium is more important
unguided media - bandwidth produced by the antenna is more important
key concerns are data rate and distance
This document summarizes different transmission media used for communication including guided media like twisted pair, coaxial cable, and optical fiber as well as unguided wireless transmission. It discusses characteristics of each medium such as bandwidth, attenuation, delay, and repeater spacing. Key concerns for any transmission include data rate, distance, and impairments from attenuation and interference. The document also provides tables comparing specifications of different cable categories and wavelength bands for optical fiber.
This document summarizes key concepts about transmission media from William Stallings' 7th edition textbook. It discusses guided media like twisted pair, coaxial cable, and optical fiber as well as unguided wireless transmission. Key factors in transmission media include bandwidth, attenuation, interference, and number of receivers. Guided media have advantages for higher data rates over longer distances while wireless has benefits for mobility but shorter range.
This chapter discusses various transmission media used for computer and data communications. It covers both guided media like twisted pair, coaxial cable, and optical fiber as well as wireless transmission methods. For each medium, it describes their characteristics such as bandwidth, attenuation, data rates, and applications. Key factors that determine the performance of different media like bandwidth, transmission impairments, and number of receivers are explained. The electromagnetic spectrum is also shown. Detailed information about technologies like antennas, radiation patterns, and wireless propagation effects are provided.
There are two main types of transmission media: guided and unguided. Guided media like twisted pair cable and coaxial cable have a physical path that signals travel along, while unguided media like wireless transmission propagate through free space. Key factors that determine the performance of a transmission medium include its bandwidth, data rate, distance capabilities, and susceptibility to interference. Common guided media include twisted pair, coaxial cable, and optical fiber, each with their own characteristics and applications for voice, data, and video transmission. Unguided or wireless transmission uses antennas to radiate signals through the air across a variety of frequency bands for applications like radio, TV, satellite, and infrared transmission.
This document discusses different types of transmission media, including their characteristics and applications. It covers both guided media like twisted pair, coaxial cable, and optical fiber, as well as unguided or wireless transmission using radio frequencies, microwaves, and satellites. Key points discussed include the factors that determine transmission quality like bandwidth and interference, the advantages of higher bandwidth and fiber optics, and how different media are suited for various uses from local networks to long-distance trunks based on their data rates and transmission distances.
Yankee Stadium implemented a wireless infrared LAN to connect cash registers to a central server for food ordering. Infrared was chosen for its low cost and ability to operate within the stadium without interfering with games. However, infrared has short range and low speeds, limiting its use to this localized application within the stadium.
The document discusses various transmission media including guided media like twisted pair, coaxial cable, and optical fiber as well as unguided media such as wireless transmission and radio. It provides details on characteristics of each medium such as data rates, distance capabilities, attenuation over frequencies, and applications. The document also reviews concepts of electromagnetic waves and provides examples of using different media for applications like local and wide area networks.
Chapter 4-Transmission Media - guided and unguided .pptxssuser32eccd
transmission medium is the physical path between transmitter and receiver
guided media – guided along a solid medium
unguided media – atmosphere, space, water
characteristics and quality determined by medium and signal
guided media - medium is more important
unguided media - bandwidth produced by the antenna is more important
key concerns are data rate and distance
This document summarizes different transmission media used for communication including guided media like twisted pair, coaxial cable, and optical fiber as well as unguided wireless transmission. It discusses characteristics of each medium such as bandwidth, attenuation, delay, and repeater spacing. Key concerns for any transmission include data rate, distance, and impairments from attenuation and interference. The document also provides tables comparing specifications of different cable categories and wavelength bands for optical fiber.
The document discusses different types of transmission media used for communication, including guided (wired) media like twisted pair, coaxial cable, and optical fiber, as well as unguided (wireless) transmission. It provides details on the characteristics of each medium, such as their bandwidth capabilities, applications, advantages and limitations. Overall, the document compares various physical transmission paths and how they enable data transmission over different distances and environments.
Transmission media can be guided or unguided. Guided media include twisted pair cable, coaxial cable, and optical fiber, which use wires or fibers to direct signals over distance. Unguided media transmit signals wirelessly using technologies like radio waves, microwaves, and satellites. The document discusses the characteristics, applications, advantages, and limitations of various transmission media types.
The document summarizes different transmission media used for telecommunications, including guided media like twisted pair cable, coaxial cable, and optical fiber, as well as unguided media like wireless transmission using terrestrial microwave, satellite microwave, broadcast radio, and infrared. It provides details on each medium's characteristics, applications, frequency ranges used, and considerations regarding distance, data rates, and susceptibility to noise and interference.
The document summarizes different transmission media used for telecommunications, including guided media like twisted pair cable, coaxial cable, and optical fiber, as well as unguided media like wireless transmission using terrestrial microwave, satellite microwave, broadcast radio, and infrared. It provides details on each medium's characteristics, applications, frequency ranges used, and considerations regarding distance, data rates, and susceptibility to noise and interference.
This chapter discusses various transmission media used for data and computer communications. It describes guided media like twisted pair cable, coaxial cable, and optical fiber which use wires, as well as unguided wireless transmission using radio waves, microwaves or satellites. Key factors in choosing a medium include available bandwidth, data transfer rates, transmission distances, and the number of receivers. The chapter then examines characteristics of common media like twisted pair cable, coaxial cable, optical fiber, terrestrial microwave, satellite, broadcast radio and infrared transmission.
Communication channels can be either guided (wired) or unguided (wireless) and are used to transmit data between a transmitter and receiver. Guided channels include twisted pair cables, coaxial cables, and optical fibers which have different bandwidth and transmission properties. Unguided channels include terrestrial microwave, satellite, and broadcast radio which propagate signals through the air. The type of channel used depends on factors like bandwidth needs, data rate, distance, and number of receivers.
Communication channels can be either guided (wired) or unguided (wireless) and are used to transmit data between a transmitter and receiver. Guided channels include twisted pair cables, coaxial cables, and optical fibers which have different bandwidth and transmission properties. Unguided channels include terrestrial microwave, satellite, and broadcast radio which propagate signals through the air. The type of channel used depends on factors like bandwidth needs, data rate, distance, and number of receivers.
Communication channels can be either guided (wired) or unguided (wireless) and are used to transmit data between a transmitter and receiver. Guided channels include twisted pair cables, coaxial cables, and optical fibers which have different bandwidth and transmission properties. Unguided channels include terrestrial microwave, satellite, and broadcast radio which propagate signals through the air. The type of channel used depends on factors like bandwidth needs, data rate, distance, and number of receivers.
This document discusses transmission fundamentals for data communications and networking. It defines key concepts such as data, signals, transmission, sources, destinations, and media. It explains how data can be transmitted through various media types including guided media like twisted pair, coaxial cable, and optical fiber as well as unguided media like radio waves, microwaves, and satellites. It also covers digital and analog signals, bandwidth, encoding data onto signals, and electromagnetic spectrum fundamentals.
This document summarizes various transmission media used for data and computer communications. It discusses both guided media like twisted pair, coaxial cable, and optical fiber as well as unguided or wireless media. Key factors in transmission include bandwidth, data rate, attenuation, interference, and the number of potential receivers. Different media have varying characteristics like maximum bandwidth, typical attenuation rates, and optimal repeater spacing. The document also examines wireless transmission frequencies, antenna types, wireless propagation techniques, and challenges like free space loss, multipath interference, and atmospheric absorption that affect wireless signals.
There are two main types of transmission media: guided and unguided. Guided media includes twisted pair cable, coaxial cable, and fiber optic cable which direct signals along a physical path. Unguided media uses wireless transmission such as radio waves, infrared, Bluetooth, WiFi, satellite. Each media type has advantages and limitations in bandwidth, distance capability, data rate, and susceptibility to interference. Fiber optic cable can support the greatest bandwidth over longest distances. Wireless technologies trade mobility for shorter range and potential interference issues.
Transmission line, single and double matchingShankar Gangaju
This document discusses different types of transmission lines used for transmitting energy and signals over long distances. It describes common transmission line media like twisted pair, coaxial cable and optical fiber. It covers their applications in telephone networks, buildings and computer networks. It also discusses their transmission characteristics and limitations. The document compares properties of unshielded and shielded twisted pair. It provides details on utilizing different wavelengths in optical fiber for various applications.
This document summarizes different types of transmission media used for data and computer communications. It discusses guided media like twisted pair, coaxial cable, and optical fiber as well as unguided wireless transmission. It describes the characteristics, bandwidth, attenuation, and limitations of each medium. Key factors that determine the quality of transmission through different media include bandwidth, transmission impairments, interference, and the number of receivers in guided media.
The document discusses various types of transmission media used for data communication, including guided media like twisted pair, coaxial cable, and optical fiber, as well as unguided wireless transmission. It covers characteristics of each medium such as bandwidth, attenuation, interference susceptibility, and data rates. Key concerns in transmission media design are maximizing bandwidth to increase data rates while minimizing transmission impairments over distance.
This document discusses different types of transmission media used in computer networks. It describes various cable types including twisted pair, coaxial, fiber optic and their characteristics. It also covers wireless transmission media like radio waves, microwaves, infrared and compares different media based on cost, speed, attenuation and interference. The document provides details on network cabling standards, fiber optic connectors, wireless frequency bands and antenna types. It concludes with comparisons of wired and wireless media.
Transmission through various mediums for communicationNeelanshi Rastogi
This document summarizes different types of transmission media, including both guided and unguided media. It discusses twisted pair, coaxial cable, optical fiber, terrestrial microwave, satellite microwave, broadcast radio, and infrared as transmission media. It also covers topics like transmission modes, wireless frequencies used, antennas, propagation methods for wireless including ground wave, sky wave and line of sight. The key aspects and applications of each transmission medium are described.
Transmission media are located below the physical layer and are used to transmit signals representing data. There are two main types of transmission media: guided media (wired), which provide a conduit for transmission, and unguided media (wireless), which transmit via electromagnetic waves without a physical pathway. Common guided media include twisted-pair cable, coaxial cable, and fiber-optic cable. Unguided media include radio waves, microwaves, and infrared. Each type of transmission media has different characteristics that determine its suitable uses.
This document discusses and compares different types of transmission media:
- Guided or wired media include twisted pair cable, coaxial cable, and optical fiber cable. These employ physical conductors to transmit data.
- Unguided or wireless media transmit data using electromagnetic waves without a physical conductor. These include radio transmission, microwave transmission, and satellite transmission.
- Each media type has advantages like capacity, cost, and limitations like range or susceptibility to interference that make some more suitable for different transmission needs. Optical fiber provides the greatest bandwidth potential over the longest distances.
The document discusses different types of transmission media used for communication, including guided (wired) media like twisted pair, coaxial cable, and optical fiber, as well as unguided (wireless) transmission. It provides details on the characteristics of each medium, such as their bandwidth capabilities, applications, advantages and limitations. Overall, the document compares various physical transmission paths and how they enable data transmission over different distances and environments.
Transmission media can be guided or unguided. Guided media include twisted pair cable, coaxial cable, and optical fiber, which use wires or fibers to direct signals over distance. Unguided media transmit signals wirelessly using technologies like radio waves, microwaves, and satellites. The document discusses the characteristics, applications, advantages, and limitations of various transmission media types.
The document summarizes different transmission media used for telecommunications, including guided media like twisted pair cable, coaxial cable, and optical fiber, as well as unguided media like wireless transmission using terrestrial microwave, satellite microwave, broadcast radio, and infrared. It provides details on each medium's characteristics, applications, frequency ranges used, and considerations regarding distance, data rates, and susceptibility to noise and interference.
The document summarizes different transmission media used for telecommunications, including guided media like twisted pair cable, coaxial cable, and optical fiber, as well as unguided media like wireless transmission using terrestrial microwave, satellite microwave, broadcast radio, and infrared. It provides details on each medium's characteristics, applications, frequency ranges used, and considerations regarding distance, data rates, and susceptibility to noise and interference.
This chapter discusses various transmission media used for data and computer communications. It describes guided media like twisted pair cable, coaxial cable, and optical fiber which use wires, as well as unguided wireless transmission using radio waves, microwaves or satellites. Key factors in choosing a medium include available bandwidth, data transfer rates, transmission distances, and the number of receivers. The chapter then examines characteristics of common media like twisted pair cable, coaxial cable, optical fiber, terrestrial microwave, satellite, broadcast radio and infrared transmission.
Communication channels can be either guided (wired) or unguided (wireless) and are used to transmit data between a transmitter and receiver. Guided channels include twisted pair cables, coaxial cables, and optical fibers which have different bandwidth and transmission properties. Unguided channels include terrestrial microwave, satellite, and broadcast radio which propagate signals through the air. The type of channel used depends on factors like bandwidth needs, data rate, distance, and number of receivers.
Communication channels can be either guided (wired) or unguided (wireless) and are used to transmit data between a transmitter and receiver. Guided channels include twisted pair cables, coaxial cables, and optical fibers which have different bandwidth and transmission properties. Unguided channels include terrestrial microwave, satellite, and broadcast radio which propagate signals through the air. The type of channel used depends on factors like bandwidth needs, data rate, distance, and number of receivers.
Communication channels can be either guided (wired) or unguided (wireless) and are used to transmit data between a transmitter and receiver. Guided channels include twisted pair cables, coaxial cables, and optical fibers which have different bandwidth and transmission properties. Unguided channels include terrestrial microwave, satellite, and broadcast radio which propagate signals through the air. The type of channel used depends on factors like bandwidth needs, data rate, distance, and number of receivers.
This document discusses transmission fundamentals for data communications and networking. It defines key concepts such as data, signals, transmission, sources, destinations, and media. It explains how data can be transmitted through various media types including guided media like twisted pair, coaxial cable, and optical fiber as well as unguided media like radio waves, microwaves, and satellites. It also covers digital and analog signals, bandwidth, encoding data onto signals, and electromagnetic spectrum fundamentals.
This document summarizes various transmission media used for data and computer communications. It discusses both guided media like twisted pair, coaxial cable, and optical fiber as well as unguided or wireless media. Key factors in transmission include bandwidth, data rate, attenuation, interference, and the number of potential receivers. Different media have varying characteristics like maximum bandwidth, typical attenuation rates, and optimal repeater spacing. The document also examines wireless transmission frequencies, antenna types, wireless propagation techniques, and challenges like free space loss, multipath interference, and atmospheric absorption that affect wireless signals.
There are two main types of transmission media: guided and unguided. Guided media includes twisted pair cable, coaxial cable, and fiber optic cable which direct signals along a physical path. Unguided media uses wireless transmission such as radio waves, infrared, Bluetooth, WiFi, satellite. Each media type has advantages and limitations in bandwidth, distance capability, data rate, and susceptibility to interference. Fiber optic cable can support the greatest bandwidth over longest distances. Wireless technologies trade mobility for shorter range and potential interference issues.
Transmission line, single and double matchingShankar Gangaju
This document discusses different types of transmission lines used for transmitting energy and signals over long distances. It describes common transmission line media like twisted pair, coaxial cable and optical fiber. It covers their applications in telephone networks, buildings and computer networks. It also discusses their transmission characteristics and limitations. The document compares properties of unshielded and shielded twisted pair. It provides details on utilizing different wavelengths in optical fiber for various applications.
This document summarizes different types of transmission media used for data and computer communications. It discusses guided media like twisted pair, coaxial cable, and optical fiber as well as unguided wireless transmission. It describes the characteristics, bandwidth, attenuation, and limitations of each medium. Key factors that determine the quality of transmission through different media include bandwidth, transmission impairments, interference, and the number of receivers in guided media.
The document discusses various types of transmission media used for data communication, including guided media like twisted pair, coaxial cable, and optical fiber, as well as unguided wireless transmission. It covers characteristics of each medium such as bandwidth, attenuation, interference susceptibility, and data rates. Key concerns in transmission media design are maximizing bandwidth to increase data rates while minimizing transmission impairments over distance.
This document discusses different types of transmission media used in computer networks. It describes various cable types including twisted pair, coaxial, fiber optic and their characteristics. It also covers wireless transmission media like radio waves, microwaves, infrared and compares different media based on cost, speed, attenuation and interference. The document provides details on network cabling standards, fiber optic connectors, wireless frequency bands and antenna types. It concludes with comparisons of wired and wireless media.
Transmission through various mediums for communicationNeelanshi Rastogi
This document summarizes different types of transmission media, including both guided and unguided media. It discusses twisted pair, coaxial cable, optical fiber, terrestrial microwave, satellite microwave, broadcast radio, and infrared as transmission media. It also covers topics like transmission modes, wireless frequencies used, antennas, propagation methods for wireless including ground wave, sky wave and line of sight. The key aspects and applications of each transmission medium are described.
Transmission media are located below the physical layer and are used to transmit signals representing data. There are two main types of transmission media: guided media (wired), which provide a conduit for transmission, and unguided media (wireless), which transmit via electromagnetic waves without a physical pathway. Common guided media include twisted-pair cable, coaxial cable, and fiber-optic cable. Unguided media include radio waves, microwaves, and infrared. Each type of transmission media has different characteristics that determine its suitable uses.
This document discusses and compares different types of transmission media:
- Guided or wired media include twisted pair cable, coaxial cable, and optical fiber cable. These employ physical conductors to transmit data.
- Unguided or wireless media transmit data using electromagnetic waves without a physical conductor. These include radio transmission, microwave transmission, and satellite transmission.
- Each media type has advantages like capacity, cost, and limitations like range or susceptibility to interference that make some more suitable for different transmission needs. Optical fiber provides the greatest bandwidth potential over the longest distances.
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2. Overview
• Guided - wire
• Unguided - wireless
• Characteristics and quality determined by
medium and signal
• For guided, the medium is more important
• For unguided, the bandwidth produced by the
antenna is more important
• Key concerns are data rate and distance
3. Design Factors
• Bandwidth
—Higher bandwidth gives higher data rate
• Transmission impairments
—Attenuation
• Interference
• Number of receivers
—In guided media
—More receivers (multi-point) introduce more
attenuation
8. Twisted Pair - Applications
• Most common medium
• Telephone network
—Between house and local exchange (subscriber loop)
• Within buildings
—To private branch exchange (PBX)
• For local area networks (LAN)
—10Mbps or 100Mbps
9. Twisted Pair - Pros and Cons
• Cheap
• Easy to work with
• Low data rate
• Short range
10. Twisted Pair - Transmission
Characteristics
• Analog
—Amplifiers every 5km to 6km
• Digital
—Use either analog or digital signals
—repeater every 2km or 3km
• Limited distance
• Limited bandwidth (1MHz)
• Limited data rate (100MHz)
• Susceptible to interference and noise
11. Near End Crosstalk
• Coupling of signal from one pair to another
• Coupling takes place when transmit signal
entering the link couples back to receiving pair
• i.e. near transmitted signal is picked up by near
receiving pair
12. Unshielded and Shielded TP
• Unshielded Twisted Pair (UTP)
—Ordinary telephone wire
—Cheapest
—Easiest to install
—Suffers from external EM interference
• Shielded Twisted Pair (STP)
—Metal braid or sheathing that reduces interference
—More expensive
—Harder to handle (thick, heavy)
13. UTP Categories
• Cat 3
— up to 16MHz
— Voice grade found in most offices
— Twist length of 7.5 cm to 10 cm
• Cat 4
— up to 20 MHz
• Cat 5
— up to 100MHz
— Commonly pre-installed in new office buildings
— Twist length 0.6 cm to 0.85 cm
• Cat 5E (Enhanced) –see tables
• Cat 6
• Cat 7
15. Twisted Pair Categories and
Classes
Category 3
Class C
Category 5
Class D
Category
5E
Category 6
Class E
Category 7
Class F
Bandwidth 16 MHz 100 MHz 100 MHz 200 MHz 600 MHz
Cable Type UTP UTP/FTP UTP/FTP UTP/FTP SSTP
Link Cost
(Cat 5 =1)
0.7 1 1.2 1.5 2.2
17. Coaxial Cable Applications
• Most versatile medium
• Television distribution
—Ariel to TV
—Cable TV
• Long distance telephone transmission
—Can carry 10,000 voice calls simultaneously
—Being replaced by fiber optic
• Short distance computer systems links
• Local area networks
18. Coaxial Cable - Transmission
Characteristics
• Analog
—Amplifiers every few km
—Closer if higher frequency
—Up to 500MHz
• Digital
—Repeater every 1km
—Closer for higher data rates
24. Frequency Utilization for Fiber
Applications
Wavelength (in
vacuum) range
(nm)
Frequency
range (THz)
Band
label
Fiber type Application
820 to 900 366 to 333 Multimode LAN
1280 to 1350 234 to 222 S Single mode Various
1528 to 1561 196 to 192 C Single mode WDM
1561 to 1620 185 to 192 L Single mode WDM
26. Wireless Transmission
Frequencies
• 2GHz to 40GHz
—Microwave
—Highly directional
—Point to point
—Satellite
• 30MHz to 1GHz
—Omnidirectional
—Broadcast radio
• 3 x 1011 to 2 x 1014
—Infrared
—Local
27. Antennas
• Electrical conductor (or system of..) used to radiate
electromagnetic energy or collect electromagnetic
energy
• Transmission
— Radio frequency energy from transmitter
— Converted to electromagnetic energy
— By antenna
— Radiated into surrounding environment
• Reception
— Electromagnetic energy impinging on antenna
— Converted to radio frequency electrical energy
— Fed to receiver
• Same antenna often used for both
28. Radiation Pattern
• Power radiated in all directions
• Not same performance in all directions
• Isotropic antenna is (theoretical) point in space
—Radiates in all directions equally
—Gives spherical radiation pattern
29. Parabolic Reflective Antenna
• Used for terrestrial and satellite microwave
• Parabola is locus of point equidistant from a line and a
point not on that line
— Fixed point is focus
— Line is directrix
• Revolve parabola about axis to get paraboloid
— Cross section parallel to axis gives parabola
— Cross section perpendicular to axis gives circle
• Source placed at focus will produce waves reflected
from parabola in parallel to axis
— Creates (theoretical) parallel beam of light/sound/radio
• On reception, signal is concentrated at focus, where
detector is placed
31. Antenna Gain
• Measure of directionality of antenna
• Power output in particular direction compared
with that produced by isotropic antenna
• Measured in decibels (dB)
• Results in loss in power in another direction
• Effective area relates to size and shape
—Related to gain
32. Terrestrial Microwave
• Parabolic dish
• Focused beam
• Line of sight
• Long haul telecommunications
• Higher frequencies give higher data rates
33. Satellite Microwave
• Satellite is relay station
• Satellite receives on one frequency, amplifies or
repeats signal and transmits on another
frequency
• Requires geo-stationary orbit
—Height of 35,784km
• Television
• Long distance telephone
• Private business networks
37. Infrared
• Modulate noncoherent infrared light
• Line of sight (or reflection)
• Blocked by walls
• e.g. TV remote control, IRD port
38. Wireless Propagation
• Signal travels along three routes
— Ground wave
• Follows contour of earth
• Up to 2MHz
• AM radio
— Sky wave
• Amateur radio, BBC world service, Voice of America
• Signal reflected from ionosphere layer of upper atmosphere
• (Actually refracted)
— Line of sight
• Above 30Mhz
• May be further than optical line of sight due to refraction
• More later…
42. Refraction
• Velocity of electromagnetic wave is a function of density
of material
— ~3 x 108 m/s in vacuum, less in anything else
• As wave moves from one medium to another, its speed
changes
— Causes bending of direction of wave at boundary
— Towards more dense medium
• Index of refraction (refractive index) is
— Sin(angle of incidence)/sin(angle of refraction)
— Varies with wavelength
• May cause sudden change of direction at transition
between media
• May cause gradual bending if medium density is varying
— Density of atmosphere decreases with height
— Results in bending towards earth of radio waves
44. Line of Sight Transmission
• Free space loss
— Signal disperses with distance
— Greater for lower frequencies (longer wavelengths)
• Atmospheric Absorption
— Water vapour and oxygen absorb radio signals
— Water greatest at 22GHz, less below 15GHz
— Oxygen greater at 60GHz, less below 30GHz
— Rain and fog scatter radio waves
• Multipath
— Better to get line of sight if possible
— Signal can be reflected causing multiple copies to be received
— May be no direct signal at all
— May reinforce or cancel direct signal
• Refraction
— May result in partial or total loss of signal at receiver